Re: [RFCv1] Media Token API needs - Was: Re: [alsa-devel] [PATCH v2 5/6] sound/usb: pcm changes to use media token api
Em Tue, 28 Oct 2014 22:00:51 -0200 Mauro Carvalho Chehab mche...@osg.samsung.com escreveu: Em Tue, 28 Oct 2014 21:42:50 -0200 Mauro Carvalho Chehab mche...@osg.samsung.com escreveu: Before starting with the description, this is the simplified diagram of a media device (without IR, eeprom and other beasts): As reference, a more complete diagram would be: An even more complete (but still simplified) diagram is shown at: http://linuxtv.org/downloads/presentations/typical_hybrid_hardware.png The dot lines represent the parts of the graph that are switched by the tuner, DMA or input select. Please notice that the DMA engines, together with the stuff needed to control A/V switches is at one single chip. Changing the registers there can affect the other streams, specially on most sophisticated devices like cx231xx, where it even has a power management IP block that validades if a device to be turned on/off won't exceed the maximum drain current of 500mA. That's basically why we need to do a temporary lock alsa, dvb, v4l and IR drivers when doing certain changes. Also, please notice that I2C buses that can be as slow as 10kbps are used to control for several devices, like: - the tuner - the Digital TV (DTV) demod - Analog and/or Video demod (sometimes embedded at the main chip) - DTV demux (sometimes embedded at the main chip) - The remote controller (sometimes embedded at the main chip) For some devices, after powered on, or when certain parameters change, a new firmware (and sometimes a hardware reset) is required. The firmware size can be about 64KB or even bigger. Also, the A/V switch it is actually two independent switches (or one switch for video and one audio mux for audio) that needs to be changed together when the source changes. Regards, Mauro For those curious enough or that are using mutt/pine this is the graph, in text mode, manually adjusted to fit into 80 cols, and with a link added by hand, as graph-easy failed to represent everything on this graph: +--+ |IR| +--+ | | v +--+ | IR POLL or DMA | +--+ | | v +--+ | devnode input8 | +--+ .. :: : +-+---+-+ : | digital| tuner | analog | : +-+---+-+ :: :: DTV IF :: off on A/V :v : +--+ : |DTV demod | : +--+ :| :| MPEG-TS :| off on A/V :v : +--+ : | demux | : +--+ :| :| MPEG-TS :| off on A/V :v : +---+-+-+ : |dvb| DMA |analog | + : +---+-+-+ | :: : | :: MPEG-TS Video stream :Video stream | :: off on A/Voff on DTV : off on DTV | :v v | : +--+ ++ | ATV IF
Re: [RFCv1] Media Token API needs - Was: Re: [alsa-devel] [PATCH v2 5/6] sound/usb: pcm changes to use media token api
On 10/28/2014 05:42 PM, Mauro Carvalho Chehab wrote: Hi Shuah, I'm understanding that you're collecting comments to write a RFC with the needs by the media token, right? I'm sending you my contributions to such text. See enclosed. I suggest to change the subject and submit this on a separate thread, after we finish the review of such document. Anyway, I'm changing the subject of this Thread to reflect that. Regards, Mauro Em Tue, 28 Oct 2014 15:15:43 -0600 Shuah Khan shua...@osg.samsung.com escreveu: On 10/27/2014 06:52 AM, Mauro Carvalho Chehab wrote: Em Sun, 26 Oct 2014 09:27:40 +0100 Takashi Iwai ti...@suse.de escreveu: Hmm... this is actually more complex than that. V4L2 driver doesn't know if ALSA is streaming or not, or even if ALSA device node is opened while he is touching at the hardware configuration or changing the state. I mean: it is not an error to set the hardware. The error only happens if ALSA and V4L2 tries to do it at the same time on an incompatible way. Also, this won't work for DVB, as on DVB this is really an exclusive lock that would prevent both ALSA and V4L2 drivers to stream while in DVB mode. Implementing it with a lock seems to be the best approach, at least on my eyes. That said, we should go back and start discussing the design goal at first. Surely. This is long, however, hoping it will describe the problem and solution that is being pursued in detail: Before starting with the description, this is the simplified diagram of a media device (without IR, eeprom and other beasts): +-+ | | | ++ +--+---++ | | | demod_video | -- | analog | tuner | digital| | | ++ +--+---++ | | | | | | | | | | | v v v v | +--+-+-+ +--+ +---+ | | dvb | DMA | analog | | demod_audio|| digital_demux | -+ +--+-+-+ +--+ +---+ | | | | | | v v v +--+ ++ +--+ | devnode dvr0 | | devnode video0 | |audio DMA | +--+ ++ +--+ | | v +--+ | devnode pcmC1D0c | +--+ There are two components that are shared there between analog and digital: the tuner (where the signal is captured) and the DMA engine used to stream analog and Digital TV (dvb). PS.: the diagram is over-simplified, as the tuner is just one of the possible inputs for the analog part of the device. Other possible inputs are S-Video, composite, HDMI, etc. Sometimes, the audio DMA is also shared, e. g. just one stream comes from the hardware. It is up to the driver to split audio and video and send them to the V4L2 and ALSA APIs. This is the case of tm6000 driver. Those shared components can be used either at analog or digital mode, but not at the same time. Also, programming the V4L2 analog and audio DMA and demods should be done via V4L2 API, as this API allows the selection of the proper audio/video input (almost all devices have multiple analog inputs). Please notice that, if the tuner is on digital mode, the entire analog path is disabled, including ALSA output. If the tuner is on analog mode, both ALSA and V4L2 can work at the same time. However, during the period where the tuner firmware is loaded, and during the DMA configuration and input selection time, neither ALSA or V4L2 can stream. Such configuration/firmware load is commanded via V4L2 API, as ALSA knows nothing about tuner or input selection. At a higher level the problem description is: There are 3 different device files that get created to control tuner and audio functions on a media device. 3 drivers (dvb, v4l2, alsa), and 3 core apis (dvb-core, v4l-core, audio) that control the tuner and audio hardware and
Re: [RFCv1] Media Token API needs - Was: Re: [alsa-devel] [PATCH v2 5/6] sound/usb: pcm changes to use media token api
Em Wed, 29 Oct 2014 10:06:51 -0600 Shuah Khan shua...@osg.samsung.com escreveu: On 10/28/2014 05:42 PM, Mauro Carvalho Chehab wrote: Hi Shuah, I'm understanding that you're collecting comments to write a RFC with the needs by the media token, right? I'm sending you my contributions to such text. See enclosed. I suggest to change the subject and submit this on a separate thread, after we finish the review of such document. Anyway, I'm changing the subject of this Thread to reflect that. Regards, Mauro Em Tue, 28 Oct 2014 15:15:43 -0600 Shuah Khan shua...@osg.samsung.com escreveu: On 10/27/2014 06:52 AM, Mauro Carvalho Chehab wrote: Em Sun, 26 Oct 2014 09:27:40 +0100 Takashi Iwai ti...@suse.de escreveu: Hmm... this is actually more complex than that. V4L2 driver doesn't know if ALSA is streaming or not, or even if ALSA device node is opened while he is touching at the hardware configuration or changing the state. I mean: it is not an error to set the hardware. The error only happens if ALSA and V4L2 tries to do it at the same time on an incompatible way. Also, this won't work for DVB, as on DVB this is really an exclusive lock that would prevent both ALSA and V4L2 drivers to stream while in DVB mode. Implementing it with a lock seems to be the best approach, at least on my eyes. That said, we should go back and start discussing the design goal at first. Surely. This is long, however, hoping it will describe the problem and solution that is being pursued in detail: Before starting with the description, this is the simplified diagram of a media device (without IR, eeprom and other beasts): +-+ | | | ++ +--+---++ | | | demod_video | -- | analog | tuner | digital| | | ++ +--+---++ | | | | || | | | || v v v v| +--+-+-+ +--+ +---+ | | dvb | DMA | analog | | demod_audio|| digital_demux | -+ +--+-+-+ +--+ +---+ | | | | | | v v v +--+ ++ +--+ | devnode dvr0 | | devnode video0 | |audio DMA | +--+ ++ +--+ | | v +--+ | devnode pcmC1D0c | +--+ There are two components that are shared there between analog and digital: the tuner (where the signal is captured) and the DMA engine used to stream analog and Digital TV (dvb). PS.: the diagram is over-simplified, as the tuner is just one of the possible inputs for the analog part of the device. Other possible inputs are S-Video, composite, HDMI, etc. Sometimes, the audio DMA is also shared, e. g. just one stream comes from the hardware. It is up to the driver to split audio and video and send them to the V4L2 and ALSA APIs. This is the case of tm6000 driver. Those shared components can be used either at analog or digital mode, but not at the same time. Also, programming the V4L2 analog and audio DMA and demods should be done via V4L2 API, as this API allows the selection of the proper audio/video input (almost all devices have multiple analog inputs). Please notice that, if the tuner is on digital mode, the entire analog path is disabled, including ALSA output. If the tuner is on analog mode, both ALSA and V4L2 can work at the same time. However, during the period where the tuner firmware is loaded, and during the DMA configuration and input selection time, neither ALSA or V4L2 can stream. Such configuration/firmware load is commanded via V4L2 API, as ALSA knows nothing about tuner or input selection. At a higher level the problem description is: There are 3 different
Re: [alsa-devel] [PATCH v2 5/6] sound/usb: pcm changes to use media token api
On 10/27/2014 06:52 AM, Mauro Carvalho Chehab wrote: Em Sun, 26 Oct 2014 09:27:40 +0100 Takashi Iwai ti...@suse.de escreveu: Hmm... this is actually more complex than that. V4L2 driver doesn't know if ALSA is streaming or not, or even if ALSA device node is opened while he is touching at the hardware configuration or changing the state. I mean: it is not an error to set the hardware. The error only happens if ALSA and V4L2 tries to do it at the same time on an incompatible way. Also, this won't work for DVB, as on DVB this is really an exclusive lock that would prevent both ALSA and V4L2 drivers to stream while in DVB mode. Implementing it with a lock seems to be the best approach, at least on my eyes. That said, we should go back and start discussing the design goal at first. Surely. This is long, however, hoping it will describe the problem and solution that is being pursued in detail: At a higher level the problem description is: There are 3 different device files that get created to control tuner and audio functions on a media device. 3 drivers (dvb, v4l2, alsa), and 3 core apis (dvb-core, v4l-core, audio) that control the tuner and audio hardware and provide user api to these 3 device files. User applications, drivers and the core have no knowledge of each other. The only thing that is common across all these drivers is the parent device for the main usb device which is controlled by the main usb driver. The premise for the main design idea in this series is creating a common construct at the parent device structure that is visible to all drivers to act as a master access control (lock). Let's call this media token object with two sub-tokens one for tuner and another for audio. Each of the apis evolved separately, hence have their own backwards compatibility to maintain. Starting with v4l2: v4l2 case: Multiple v4l2 applications are allowed to open /dev/video0 in read/write mode with no restrictions as long as the tuner is in analog mode. v4l2 core handles conflicting requests between v4l2 applications. It doesn't have the knowledge that the tuner is in use by a dvb and/or audio is in use. As soon as a v4l2 application starts, digital stream glitches and audio glitches. dvb case: Multiple dvb applications can open the dvb device in read only mode. As soon an application open the device read/write mode a separate kthread is kicked off to handle the request. Only one application can open the device in read/write mode. Similar to v4l2 case, dvb-core doesn't have any knowledge that the tuner is in use by v4l2 and/or audio is in use. As soon as a dvb application starts v4l2 video glitches and audio glitches. audio case: Same scenario is applicable to audio application. When a v4l2 or dvb application starts, audio application gets impacted. Problems to address: dvb owns tuner and audio: another dvb, v4l2 app and audio app should detect tuner/audio busy right away and exit. v4l2 owns tuner and audio: another dvb and audio app should detect tuner/audio busy right away and exit. v4l2 app can continue to use it until it tries to change the tuner/audio state. audio owns audio: dvb and v4l2 apps should detect audio busy and exit. Special cases: dvb apps. access tuner and audio in exclusive mode. i.e only one dvb app. at a time is allowed to open the device read/write mode. As dvb apps. create threads to handle audio and video, all threads in that group should be allowed by the higher level construct to access the tuner and audio. dvb application will have to hold tuner and audio tokens so v4l2 and audio apps. know they are in use. audio apps. access audio in exclusive mode. i.e only one audio app. at a time is allowed to open the device in read/write mode. Audio apps. create threads and thread closes and re-opens the audio device. Threads can do this and hence something that higher level construct has to allow. audio app. has to hold audio token so dvb and v4l2 know that it is in use. (Note: I am not sure if I have the audio scenario right) v4l2 apps. access tuner and audio in shared v4l2 mode. i.e several v4l2 processes and threads could use tuner and audio at the same time. The higher level construct has to allow multiple v4l2 apps. to access and disallow dvb and audio apps. access when they are in use by v4l2. Adding to this, both dvb and v4l2 open audio device and make snd pcm capture callbacks. There is no way to tell if dvb or v4l2 or audio app is the one that is making this request. dvb app would like audio in exclusive mode allowing only one process and its threads to access it. v4l2 on the other hand would like audio in shared state accessible to all v4l2 processes. If dvb-core and v4l2-core get tuner and audio tokens at the same time, the window for having tuner token and not getting audio token go down. In dvb case when dvb device is opened in
[RFCv1] Media Token API needs - Was: Re: [alsa-devel] [PATCH v2 5/6] sound/usb: pcm changes to use media token api
Hi Shuah, I'm understanding that you're collecting comments to write a RFC with the needs by the media token, right? I'm sending you my contributions to such text. See enclosed. I suggest to change the subject and submit this on a separate thread, after we finish the review of such document. Anyway, I'm changing the subject of this Thread to reflect that. Regards, Mauro Em Tue, 28 Oct 2014 15:15:43 -0600 Shuah Khan shua...@osg.samsung.com escreveu: On 10/27/2014 06:52 AM, Mauro Carvalho Chehab wrote: Em Sun, 26 Oct 2014 09:27:40 +0100 Takashi Iwai ti...@suse.de escreveu: Hmm... this is actually more complex than that. V4L2 driver doesn't know if ALSA is streaming or not, or even if ALSA device node is opened while he is touching at the hardware configuration or changing the state. I mean: it is not an error to set the hardware. The error only happens if ALSA and V4L2 tries to do it at the same time on an incompatible way. Also, this won't work for DVB, as on DVB this is really an exclusive lock that would prevent both ALSA and V4L2 drivers to stream while in DVB mode. Implementing it with a lock seems to be the best approach, at least on my eyes. That said, we should go back and start discussing the design goal at first. Surely. This is long, however, hoping it will describe the problem and solution that is being pursued in detail: Before starting with the description, this is the simplified diagram of a media device (without IR, eeprom and other beasts): +-+ | | | ++ +--+---++ | | | demod_video | -- | analog | tuner | digital| | | ++ +--+---++ | | | | | | | | | | | v v v v | +--+-+-+ +--+ +---+ | | dvb | DMA | analog | | demod_audio|| digital_demux | -+ +--+-+-+ +--+ +---+ | | | | | | v v v +--+ ++ +--+ | devnode dvr0 | | devnode video0 | |audio DMA | +--+ ++ +--+ | | v +--+ | devnode pcmC1D0c | +--+ There are two components that are shared there between analog and digital: the tuner (where the signal is captured) and the DMA engine used to stream analog and Digital TV (dvb). PS.: the diagram is over-simplified, as the tuner is just one of the possible inputs for the analog part of the device. Other possible inputs are S-Video, composite, HDMI, etc. Sometimes, the audio DMA is also shared, e. g. just one stream comes from the hardware. It is up to the driver to split audio and video and send them to the V4L2 and ALSA APIs. This is the case of tm6000 driver. Those shared components can be used either at analog or digital mode, but not at the same time. Also, programming the V4L2 analog and audio DMA and demods should be done via V4L2 API, as this API allows the selection of the proper audio/video input (almost all devices have multiple analog inputs). Please notice that, if the tuner is on digital mode, the entire analog path is disabled, including ALSA output. If the tuner is on analog mode, both ALSA and V4L2 can work at the same time. However, during the period where the tuner firmware is loaded, and during the DMA configuration and input selection time, neither ALSA or V4L2 can stream. Such configuration/firmware load is commanded via V4L2 API, as ALSA knows nothing about tuner or input selection. At a higher level the problem description is: There are 3 different device files that get created to control tuner and audio functions on a media device. 3 drivers (dvb, v4l2, alsa), and 3 core apis (dvb-core, v4l-core, audio) that control the tuner and audio hardware and provide user api to these 3 device files. There's actually a 4th component for some drivers: the mceusb
Re: [RFCv1] Media Token API needs - Was: Re: [alsa-devel] [PATCH v2 5/6] sound/usb: pcm changes to use media token api
Em Tue, 28 Oct 2014 21:42:50 -0200
Mauro Carvalho Chehab mche...@osg.samsung.com escreveu:
Before starting with the description, this is the simplified diagram of
a media device (without IR, eeprom and other beasts):
As reference, a more complete diagram would be:
+--+
|IR
|
+--+
|
|
v
+--+
| IR POLL or
DMA |
+--+
|
|
v
+--+
| devnode
input8 |
+--+
++
v|
++
+---+---+---+
| demod_video | +- | tuner | A/V switch
| composite |
++ |
+---+---+---+
| | |
| | |
v | v
+--+-+-+ |
+--+
+- | dvb | DMA | analog | || demod_audio
|
| +--+-+-+ |
+--+
|^ | | |
|+---+ | | |
|| v | v
| +--+ | ++ |
+--+
+ | devnode dvr0 | | | devnode video0 | ||audio DMA
|
+--+ | ++ |
+--+
| | |
| | |
| | v
| |
+--+
| || devnode
pcmC1D0c |
| |
+--+
| |
| |
| |
|
+++---+
| | analog | tuner | digital
|
|
+++---+
| |
| |
| v
|
+--+
+--- |
digital_demux |
+--+
Regards,
Mauro
-
Dot file for the above diagram:
digraph media_hardware {
node [shape=record]
DMA1[label = dvb dvb | dma DMA | video analog]
DMA2[label = audio DMA]
DMA3[label = IR POLL or DMA]
tuner[label = analog analog | tuner tuner | digital digital]
input[label = tuner tuner | switch A/V switch | composite composite]
DMA1:video - devnode video0
DMA1:dvb - devnode dvr0
digital_demux - DMA1:dvb
demod_video - DMA1:video
tuner:digital - digital_demux
tuner:analog - input:tuner
input:switch - demod_video
input:switch - demod_audio
demod_audio - DMA2
DMA2 - devnode pcmC1D0c
IR - DMA3
DMA3 - devnode input8
}
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Re: [alsa-devel] [PATCH v2 5/6] sound/usb: pcm changes to use media token api
Em Sun, 26 Oct 2014 09:27:40 +0100 Takashi Iwai ti...@suse.de escreveu: At Sat, 25 Oct 2014 11:41:15 -0200, Mauro Carvalho Chehab wrote: +---+ | start | +---+ | | v ++ | idle | + ++ | |^ || || || v| || +---+ | || | configuration | | || +---+ | || || || || || v| || +---+ | || + | streaming | -+ || | +---+ || |||| |||| |vv| | +---+---++ | +- | 1 | suspended | 2 | -+ +---+---++ The above diagram is actually simplified. There's an extra state there that should be mentioned: idle - DVB stream (actually, DVB stream is a copy of the above, except that ALSA won't have any business to do while the device is on DVB mode) So, judging from your description, the problem isn't about the exclusive lock, but rather implementation a kind of master/slave devices? Then the proposed patch doesn't look like a correct implementation to me. You might see it as a master/slave, except that it is not that simple. It is really a hardware lock. There are actually 3 (sub)drivers that may need to set the hardware: - ALSA driver; - V4L2 driver; - DVB driver. The goal of the lock is to prevent that more than one driver would try to use a common piece of the hardware that it is already in usage by another driver. So, for example, the ALSA driver should not reprogram the hardware while the V4L2 driver is doing that. I agree that, for V4L2/ALSA driver's interaction PoV, it could resemble a sort of master/slave control, in the sense that ALSA capture start only makes sense while V4L2 is at streaming state. Yet, just opening the device or (even start capture on ALSA, for the hardware with multiple DMA engines, like the ones that use snd-usb-audio) won't cause any harm if the V4L2 driver is not reconfiguring the audio registers at the same time. Also, ALSA open/close should be supported any time, as otherwise it will break existing applications. However, when the device is streaming on DVB mode, it is not possible to stream on V4L2 mode, as there's just one DMA for both and just one tuner. Also, ALSA capture doesn't make much sense on such case. Still, locking on open/close may eventually break existing applications. Also, it doesn't really make any sense to block the device to move from analog to digital mode just because the ALSA devnodes are opened. What I (and supposedly Pierre) opposed is the implementation of exclusive lock control in spontaneous callbacks. Especially the trigger callback is a bad place since it's a callback that is supposed to just trigger atomically. In general, the only good place for allowing user-space to *control* the exclusive lock is open/close, unless the finer lock control is exposed. I see your point. Then perhaps we should expose callbacks from other parts of the ALSA core, perhaps at the logic that calls the trigger callback at read and poll syscalls, plus the corresponding logic that is used when the device is using the mmap syscall. But, reading through the argument from you guys, the intention of the patch seems like just to raise the conflict from the hardware level to the software level. Yes. If so, I doubt whether such an exclusive lock is the best way. For example, audio stream can simply receive an error at any time if something is wrong and reacts accordingly instead of keeping the lock while streaming. Then the master side (video) can set the error flag, let the audio stream stop in the driver (if running), and sync with it. Hmm... this is actually more complex than that. V4L2 driver doesn't know if ALSA is streaming or not, or even if ALSA device node is opened while he is touching at the hardware configuration or changing the state. I mean: it is not an error to set the hardware. The error only happens if ALSA and V4L2 tries to do it at the same time on an incompatible way. Also, this won't work for DVB, as on DVB this is really an exclusive lock that would prevent both ALSA and V4L2 drivers to stream while in DVB mode. Implementing it with a lock seems to be the best approach, at least on my eyes. That said, we should go back and start discussing the design goal at first. Surely. thanks, Takashi -- To unsubscribe
Re: [alsa-devel] [PATCH v2 5/6] sound/usb: pcm changes to use media token api
On 10/25/2014 04:57 AM, Mauro Carvalho Chehab wrote: Hi, Sorry to enter into this thread so late. Last week was a full week, due to the 4 conferences I paticiapated, and last week I needed to fill lots of trip reports. Also, I have another trip to give two speeches. Em Tue, 21 Oct 2014 11:32:10 -0600 Shuah Khan shua...@osg.samsung.com escreveu: Here is what I propose for patch v3: - make it a module under media - collapse tuner and audio tokens into media token I'm a little skeptical about this. Merging tuner and audio tokens seems weird on my eyes, as there are actually two different hardware resources we need to lock, and we may be locking them on different places. I think the suggestion for collapsing came about because, in this patch series, the dvb and v4l use-cases are such that tuner and audio need to be held together. i.e when tuner is held, audio is held as well. With an intent to simplify the usage, I decided to have get_tuner interface to return audio token. It does simplify the logic for callers - all the paces that get tuner will also need to make a call to get audio and handle errors when audio is not available. That made it even more confusing perhaps and raised the question that why can't we collapse. Having two tokens will allow the ability hold them independently. Maybe the right approach for patch v3 is don't collapse, but change dvb and v4l to get tuner followed by audio and handle the errors paths themselves. - change names (get rid of abbreviated tkn stuff) - Make other changes Takashi/Lars pointed out in pcm - hold token in pcm open/close -- Shuah -- Shuah Khan Sr. Linux Kernel Developer Samsung Research America (Silicon Valley) shua...@osg.samsung.com | (970) 217-8978 -- To unsubscribe from this list: send the line unsubscribe linux-media in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [alsa-devel] [PATCH v2 5/6] sound/usb: pcm changes to use media token api
At Sat, 25 Oct 2014 11:41:15 -0200, Mauro Carvalho Chehab wrote: (re-sending from my third e-mail - somehow, the two emails I have at Samsung didn't seem to be delivering to vger.kernel.org today) Em Wed, 22 Oct 2014 14:26:41 -0500 Pierre-Louis Bossart pierre-louis.boss...@linux.intel.com escreveu: On 10/21/14, 11:08 AM, Devin Heitmueller wrote: Sorry, I'm not convinced by that. If the device has to be controlled exclusively, the right position is the open/close. Otherwise, the program cannot know when it becomes inaccessible out of sudden during its operation. I can say that I've definitely seen cases where if you configure a device as the default capture device in PulseAudio, then pulse will continue to capture from it even if you're not actively capturing the audio from pulse. I only spotted this because I had a USB analyzer on the device and was dumbfounded when the ISOC packets kept arriving even after I had closed VLC. this seems like a feature, not a bug. PulseAudio starts streaming before clients push any data and likewise keeps sources active even after for some time after clients stop recording. Closing VLC in your example doesn't immediately close the ALSA device. look for module-suspend-on-idle in your default.pa config file. This could be a feature for an audio capture device that is standalone, but for sure it isn't a feature for an audio capture device where the audio is only available if video is also being streamed. A V4L device with ALSA capture is a different beast than a standalone capture port. In a simplified way, it will basically follow the following state machine: +---+ | start | +---+ | | v ++ | idle | + ++ | |^ || || || v| || +---+ | || | configuration | | || +---+ | || || || || || v| || +---+ | || + | streaming | -+ || | +---+ || |||| |||| |vv| | +---+---++ | +- | 1 | suspended | 2 | -+ +---+---++ 1) start state This is when the V4L2 device gots probed. It checks if the hardware is present and initializes some vars/registers, turning off everything that can be powered down. The tuner on put in sleep mode, analog audio/video decoders and the dvb frontend and demux are also turned off. 2) idle state As the device is powered off, audio won't produce anything. Depending on the device, reading for audio may return a sequence of zeros, or may even fail, as the DMA engine is not ready yet for streaming. Also, the audio mixer is muted, but the audio input switch is on a random state. 2) configuration state When V4L2 node device is opened and configured, the audio mixer will be switched to input audio from the same source of the video stream. The corresponding audio input is also unmuted. Almost all devices have at least two audio/video inputs: TV TUNER and COMPOSITE. Other devices may also have S-VIDEO, COMPOSITE 2, RADIO TUNER, etc. If the device is set on TUNER mode, on modern devices, a tuner firmware will be loaded. That may require a long time. Typically, most devices take 1/2 seconds to load a firmware, but some devices may take up to 30 seconds. The firmware may depend on the TV standard that will be used, so this can't be loaded at driver warm up state. Also, the power consumption of the tuners is high (it can be ~100-200 mW or more when powered, and ~16mW when just I2C is powered). We don't want to keep it powered when the device is not used, as this spends battery. Also, the life of the device reduces a lot if we keep it always powered. During this stage, if an ALSA call is issued, it may interfere at the device settings and/or firmware load, with can cause the audio to fail. On such cases, applications might need to close the V4L2 node and re-open again. 3) streaming state The change to this staging requires a V4L2 ioctl. Please notice, however, that some apps will open the audio device before the V4L2 node, while others will open it after that. In any case, audio will only start to produce data after the V4L2 ioctl at V4L2 that starts the DMA engine there. After that ioctl: - Audio PCM capture will work; - The mixers will be in a good state: unmuted,
Re: [alsa-devel] [PATCH v2 5/6] sound/usb: pcm changes to use media token api
(re-sending from my third e-mail - somehow, the two emails I have at Samsung didn't seem to be delivering to vger.kernel.org today) Em Wed, 22 Oct 2014 14:26:41 -0500 Pierre-Louis Bossart pierre-louis.boss...@linux.intel.com escreveu: On 10/21/14, 11:08 AM, Devin Heitmueller wrote: Sorry, I'm not convinced by that. If the device has to be controlled exclusively, the right position is the open/close. Otherwise, the program cannot know when it becomes inaccessible out of sudden during its operation. I can say that I've definitely seen cases where if you configure a device as the default capture device in PulseAudio, then pulse will continue to capture from it even if you're not actively capturing the audio from pulse. I only spotted this because I had a USB analyzer on the device and was dumbfounded when the ISOC packets kept arriving even after I had closed VLC. this seems like a feature, not a bug. PulseAudio starts streaming before clients push any data and likewise keeps sources active even after for some time after clients stop recording. Closing VLC in your example doesn't immediately close the ALSA device. look for module-suspend-on-idle in your default.pa config file. This could be a feature for an audio capture device that is standalone, but for sure it isn't a feature for an audio capture device where the audio is only available if video is also being streamed. A V4L device with ALSA capture is a different beast than a standalone capture port. In a simplified way, it will basically follow the following state machine: +---+ | start | +---+ | | v ++ | idle | + ++ | |^ || || || v| || +---+ | || | configuration | | || +---+ | || || || || || v| || +---+ | || + | streaming | -+ || | +---+ || |||| |||| |vv| | +---+---++ | +- | 1 | suspended | 2 | -+ +---+---++ 1) start state This is when the V4L2 device gots probed. It checks if the hardware is present and initializes some vars/registers, turning off everything that can be powered down. The tuner on put in sleep mode, analog audio/video decoders and the dvb frontend and demux are also turned off. 2) idle state As the device is powered off, audio won't produce anything. Depending on the device, reading for audio may return a sequence of zeros, or may even fail, as the DMA engine is not ready yet for streaming. Also, the audio mixer is muted, but the audio input switch is on a random state. 2) configuration state When V4L2 node device is opened and configured, the audio mixer will be switched to input audio from the same source of the video stream. The corresponding audio input is also unmuted. Almost all devices have at least two audio/video inputs: TV TUNER and COMPOSITE. Other devices may also have S-VIDEO, COMPOSITE 2, RADIO TUNER, etc. If the device is set on TUNER mode, on modern devices, a tuner firmware will be loaded. That may require a long time. Typically, most devices take 1/2 seconds to load a firmware, but some devices may take up to 30 seconds. The firmware may depend on the TV standard that will be used, so this can't be loaded at driver warm up state. Also, the power consumption of the tuners is high (it can be ~100-200 mW or more when powered, and ~16mW when just I2C is powered). We don't want to keep it powered when the device is not used, as this spends battery. Also, the life of the device reduces a lot if we keep it always powered. During this stage, if an ALSA call is issued, it may interfere at the device settings and/or firmware load, with can cause the audio to fail. On such cases, applications might need to close the V4L2 node and re-open again. 3) streaming state The change to this staging requires a V4L2 ioctl. Please notice, however, that some apps will open the audio device before the V4L2 node, while others will open it after that. In any case, audio will only start to produce data after the V4L2 ioctl at V4L2 that starts the DMA engine there. After that ioctl: - Audio PCM capture will work; - The mixers will be in a good state: unmuted, and switched to the corresponding input as the video stream. If the user wants to do something unusual, like mixing the composite audio input with the tuner audio input, it can use the
Re: [alsa-devel] [PATCH v2 5/6] sound/usb: pcm changes to use media token api
(re-sending from my other e-mail - somehow, the email I sent via m.che...@samsung.com doesn't seem to be delivered at vger.kernel.org) Em Wed, 22 Oct 2014 14:26:41 -0500 Pierre-Louis Bossart pierre-louis.boss...@linux.intel.com escreveu: On 10/21/14, 11:08 AM, Devin Heitmueller wrote: Sorry, I'm not convinced by that. If the device has to be controlled exclusively, the right position is the open/close. Otherwise, the program cannot know when it becomes inaccessible out of sudden during its operation. I can say that I've definitely seen cases where if you configure a device as the default capture device in PulseAudio, then pulse will continue to capture from it even if you're not actively capturing the audio from pulse. I only spotted this because I had a USB analyzer on the device and was dumbfounded when the ISOC packets kept arriving even after I had closed VLC. this seems like a feature, not a bug. PulseAudio starts streaming before clients push any data and likewise keeps sources active even after for some time after clients stop recording. Closing VLC in your example doesn't immediately close the ALSA device. look for module-suspend-on-idle in your default.pa config file. This could be a feature for an audio capture device that is standalone, but for sure it isn't a feature for an audio capture device where the audio is only available if video is also being streamed. A V4L device with ALSA capture is a different beast than a standalone capture port. In a simplified way, it will basically follow the following state machine: +---+ | start | +---+ | | v ++ | idle | + ++ | |^ || || || v| || +---+ | || | configuration | | || +---+ | || || || || || v| || +---+ | || + | streaming | -+ || | +---+ || |||| |||| |vv| | +---+---++ | +- | 1 | suspended | 2 | -+ +---+---++ 1) start state This is when the V4L2 device gots probed. It checks if the hardware is present and initializes some vars/registers, turning off everything that can be powered down. The tuner on put in sleep mode, analog audio/video decoders and the dvb frontend and demux are also turned off. 2) idle state As the device is powered off, audio won't produce anything. Depending on the device, reading for audio may return a sequence of zeros, or may even fail, as the DMA engine is not ready yet for streaming. Also, the audio mixer is muted, but the audio input switch is on a random state. 2) configuration state When V4L2 node device is opened and configured, the audio mixer will be switched to input audio from the same source of the video stream. The corresponding audio input is also unmuted. Almost all devices have at least two audio/video inputs: TV TUNER and COMPOSITE. Other devices may also have S-VIDEO, COMPOSITE 2, RADIO TUNER, etc. If the device is set on TUNER mode, on modern devices, a tuner firmware will be loaded. That may require a long time. Typically, most devices take 1/2 seconds to load a firmware, but some devices may take up to 30 seconds. The firmware may depend on the TV standard that will be used, so this can't be loaded at driver warm up state. Also, the power consumption of the tuners is high (it can be ~100-200 mW or more when powered, and ~16mW when just I2C is powered). We don't want to keep it powered when the device is not used, as this spends battery. Also, the life of the device reduces a lot if we keep it always powered. During this stage, if an ALSA call is issued, it may interfere at the device settings and/or firmware load, with can cause the audio to fail. On such cases, applications might need to close the V4L2 node and re-open again. 3) streaming state The change to this staging requires a V4L2 ioctl. Please notice, however, that some apps will open the audio device before the V4L2 node, while others will open it after that. In any case, audio will only start to produce data after the V4L2 ioctl at V4L2 that starts the DMA engine there. After that ioctl: - Audio PCM capture will work; - The mixers will be in a good state: unmuted, and switched to the corresponding input as the video stream. If the user wants to do something unusual, like mixing the composite audio input with the tuner audio input, it can use
Re: [alsa-devel] [PATCH v2 5/6] sound/usb: pcm changes to use media token api
Em Wed, 22 Oct 2014 14:26:41 -0500 Pierre-Louis Bossart pierre-louis.boss...@linux.intel.com escreveu: On 10/21/14, 11:08 AM, Devin Heitmueller wrote: Sorry, I'm not convinced by that. If the device has to be controlled exclusively, the right position is the open/close. Otherwise, the program cannot know when it becomes inaccessible out of sudden during its operation. I can say that I've definitely seen cases where if you configure a device as the default capture device in PulseAudio, then pulse will continue to capture from it even if you're not actively capturing the audio from pulse. I only spotted this because I had a USB analyzer on the device and was dumbfounded when the ISOC packets kept arriving even after I had closed VLC. this seems like a feature, not a bug. PulseAudio starts streaming before clients push any data and likewise keeps sources active even after for some time after clients stop recording. Closing VLC in your example doesn't immediately close the ALSA device. look for module-suspend-on-idle in your default.pa config file. This could be a feature for an audio capture device that is standalone, but for sure it isn't a feature for an audio capture device where the audio is only available if video is also being streamed. A V4L device with ALSA capture is a different beast than a standalone capture port. In a simplified way, it will basically follow the following state machine: +---+ | start | +---+ | | v ++ | idle | + ++ | |^ || || || v| || +---+ | || | configuration | | || +---+ | || || || || || v| || +---+ | || + | streaming | -+ || | +---+ || |||| |||| |vv| | +---+---++ | +- | 1 | suspended | 2 | -+ +---+---++ 1) start state This is when the V4L2 device gots probed. It checks if the hardware is present and initializes some vars/registers, turning off everything that can be powered down. The tuner on put in sleep mode, analog audio/video decoders and the dvb frontend and demux are also turned off. 2) idle state As the device is powered off, audio won't produce anything. Depending on the device, reading for audio may return a sequence of zeros, or may even fail, as the DMA engine is not ready yet for streaming. Also, the audio mixer is muted, but the audio input switch is on a random state. 2) configuration state When V4L2 node device is opened and configured, the audio mixer will be switched to input audio from the same source of the video stream. The corresponding audio input is also unmuted. Almost all devices have at least two audio/video inputs: TV TUNER and COMPOSITE. Other devices may also have S-VIDEO, COMPOSITE 2, RADIO TUNER, etc. If the device is set on TUNER mode, on modern devices, a tuner firmware will be loaded. That may require a long time. Typically, most devices take 1/2 seconds to load a firmware, but some devices may take up to 30 seconds. The firmware may depend on the TV standard that will be used, so this can't be loaded at driver warm up state. Also, the power consumption of the tuners is high (it can be ~100-200 mW or more when powered, and ~16mW when just I2C is powered). We don't want to keep it powered when the device is not used, as this spends battery. Also, the life of the device reduces a lot if we keep it always powered. During this stage, if an ALSA call is issued, it may interfere at the device settings and/or firmware load, with can cause the audio to fail. On such cases, applications might need to close the V4L2 node and re-open again. 3) streaming state The change to this staging requires a V4L2 ioctl. Please notice, however, that some apps will open the audio device before the V4L2 node, while others will open it after that. In any case, audio will only start to produce data after the V4L2 ioctl at V4L2 that starts the DMA engine there. After that ioctl: - Audio PCM capture will work; - The mixers will be in a good state: unmuted, and switched to the corresponding input as the video stream. If the user wants to do something unusual, like mixing the composite audio input with the tuner audio input, it can use the ALSA mixer for doing that. Otherwise, the only part of the ALSA device that will be used is the PCM engine. 4) streaming-stop
Re: [alsa-devel] [PATCH v2 5/6] sound/usb: pcm changes to use media token api
On 10/22/2014 01:45 PM, Devin Heitmueller wrote: this seems like a feature, not a bug. PulseAudio starts streaming before clients push any data and likewise keeps sources active even after for some time after clients stop recording. Closing VLC in your example doesn't immediately close the ALSA device. look for module-suspend-on-idle in your default.pa config file. The ALSA userland emulation in PulseAudio is supposed to faithfully emulate the behavior of the ALSA kernel ABI... except when it doesn't, then it's not a bug but rather a feature. :-) I also agree that the open/close of the alsa device is the only way to control exclusion. I was also a proponent that we should have fairly coarse locking done at open/close for the various device nodes (ALSA/V4L/DVB). The challenge here is that we have a large installed based of existing applications that rely on kernel behavior that isn't formally specified in any specification. Hence we're forced to try to come up with a solution that minimizes the risk of ABI breakage. If we were doing this from scratch then we could lay down some hard/fast rules about things apps aren't supposed to do and how apps are supposed to respond to those exception cases. Unfortunately we don't have that luxury here. Sounds like we don't have a clear direction on open/close or capture start/stop. What I am hearing is open/close isn't acceptable for media maintainers and capture trigger start/stop isn't acceptable to sound maintainers. :) Fork in the road, which way do we go? Implementation wise, supporting capture trigger start/stop approach will be harder to maintain in longterm. It adds more variables to the mix. Applications open sounds device from the main thread and then create a new thread to handle streams. I can see that based on the token hold requests that come in. So the token hold logic will have to take that into account, leading into potential unbalanced lock/unlock scenarios. It is not impossible to solve, that's what I did in this patch series, but it does get complex. What I am looking for is some consensus on let's go with an approach and try. Doesn't matter which way we go, and how much testing I do, I am bound to miss something and this work needs to soak for a bit in the media experimental branch. thanks, -- Shuah -- Shuah Khan Sr. Linux Kernel Developer Samsung Research America (Silicon Valley) shua...@osg.samsung.com | (970) 217-8978 -- To unsubscribe from this list: send the line unsubscribe linux-media in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [alsa-devel] [PATCH v2 5/6] sound/usb: pcm changes to use media token api
Hi Shuah, Some notes below... On 10/21/2014 07:32 PM, Shuah Khan wrote: On 10/21/2014 10:05 AM, Takashi Iwai wrote: At Tue, 21 Oct 2014 17:42:51 +0200, Hans Verkuil wrote: Quite often media apps open the alsa device at the start and then switch between TV, radio or DVB mode. If the alsa device would claim the tuner just by being opened (as opposed to actually using the tuner, which happens when you start streaming), What about parameter changes? The sound devices have to be configured before using. Don't they influence on others at all, i.e. you can change the PCM sample rate etc during TV, radio or DVB is running? Yes. kaffeine uses snd_usb_capture_ops ioctl - snd_pcm_lib_ioctl Other v4l and vlc (dvb) uses open/close as well as trigger start and stop. trigger start/stop is done by a special audio thread in some cases. open/close happens from the main thread. then that would make it impossible for the application to switch tuner mode. In general you want to avoid that open() will start configuring hardware since that can quite often be slow. Tuner configuration in particular can be slow since several common tuners need to load firmware over i2c. You only want to do that when it is really needed, and not when some application (udev!) opens the device just to examine what sort of device it is. But most apps close the device soon after that, no? Which programs keep the PCM device (not the control) opened without actually using? So claiming the tuner in the trigger seems to be the right place. If returning EBUSY is a poor error code for alsa, then we can use something else for that. EACCES perhaps? Sorry, I'm not convinced by that. If the device has to be controlled exclusively, the right position is the open/close. Otherwise, the program cannot know when it becomes inaccessible out of sudden during its operation. Let me share my test matrix for this patch series. Hans pointed out one test case I didn't know about as a result missed testing. Please see if any of the tests miss use-cases or break them: you can scroll down to the proposal at the end, if this is too much detail :) Digital active and analog starting testing: kaffeine running - v4l2-ctl --all - works I would recommend using v4l2-ctl --all --list-inputs, this enumerates inputs as well (which includes reading the tuner status). This would have failed with all these tests with this patch series. - Changing channels works with the same token hold, even when frequency changes. Tested changing channels that force freq change. - vlc resource is busy with no disruption to kaffeine - xawtv - tuner busy when it tries to do ioctls that change tuner settings - snd_usb_pcm_open detects device is busy ( pcm open called from the same thread, trigger gets called from another thread ) - tvtime - tuner busy when it tries to do ioctls that change tuner settings with no disruption to kaffeine ( pcm open called from the same thread, trigger gets called from another thread ) - vlc - audio capture on WinTV HVR-950 - device is busy start vlc with no channels for this test - arecord to capture on WinTV HVR-950 - device busy vlc running vlc -v channels.xspf - v4l2-ctl --all - works - Changing channels works with the same token hold, even when frequency changes. Tested changing channels that force freq change. - kaffeine resource is busy with no disruption to vlc - xawtv - tuner busy when it tries to do ioctls that change tuner settings - snd_usb_pcm_open detects device is busy ( pcm open called from the same thread, trigger gets called from another thread ) - tvtime - tuner busy when it tries to do ioctls that change tuner settings with no disruption to kaffeine ( pcm open called from the same thread, trigger gets called from another thread ) - vlc - audio capture on WinTV HVR-950 - device is busy - arecord to capture on WinTV HVR-950 - device busy Analog active and start digital testing: xawtv -noalsa -c /dev/video1 - v4l2-ctl --all - works - start kaffeine - fails with device busy and no disruption - start vlc - fails with device busy and no disruption - tvtime - tuner busy when it tries to do ioctls that change tuner settings with no disruption to kaffeine - vlc - audio capture on WinTV HVR-950 - device is busy - arecord to capture on WinTV HVR-950 - device busy tvtime - v4l2-ctl --all - works - start kaffeine - fails with device busy and no disruption - start vlc - fails with device busy and no disruption - xawtv - tuner busy when it tries to do ioctls that change tuner settings with no disruption to kaffeine - vlc - audio capture on WinTV HVR-950 - device is busy - arecord to capture on WinTV HVR-950 - device busy The following audio/video start/stop combination tests: ( used arecord as well to test these cases, arecord ) - tvtime start/vlc start/vlc stop/tvtime stop no disruption to
Re: [alsa-devel] [PATCH v2 5/6] sound/usb: pcm changes to use media token api
On 10/21/14, 11:08 AM, Devin Heitmueller wrote: Sorry, I'm not convinced by that. If the device has to be controlled exclusively, the right position is the open/close. Otherwise, the program cannot know when it becomes inaccessible out of sudden during its operation. I can say that I've definitely seen cases where if you configure a device as the default capture device in PulseAudio, then pulse will continue to capture from it even if you're not actively capturing the audio from pulse. I only spotted this because I had a USB analyzer on the device and was dumbfounded when the ISOC packets kept arriving even after I had closed VLC. this seems like a feature, not a bug. PulseAudio starts streaming before clients push any data and likewise keeps sources active even after for some time after clients stop recording. Closing VLC in your example doesn't immediately close the ALSA device. look for module-suspend-on-idle in your default.pa config file. I also agree that the open/close of the alsa device is the only way to control exclusion. -Pierre -- To unsubscribe from this list: send the line unsubscribe linux-media in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [alsa-devel] [PATCH v2 5/6] sound/usb: pcm changes to use media token api
this seems like a feature, not a bug. PulseAudio starts streaming before clients push any data and likewise keeps sources active even after for some time after clients stop recording. Closing VLC in your example doesn't immediately close the ALSA device. look for module-suspend-on-idle in your default.pa config file. The ALSA userland emulation in PulseAudio is supposed to faithfully emulate the behavior of the ALSA kernel ABI... except when it doesn't, then it's not a bug but rather a feature. :-) I also agree that the open/close of the alsa device is the only way to control exclusion. I was also a proponent that we should have fairly coarse locking done at open/close for the various device nodes (ALSA/V4L/DVB). The challenge here is that we have a large installed based of existing applications that rely on kernel behavior that isn't formally specified in any specification. Hence we're forced to try to come up with a solution that minimizes the risk of ABI breakage. If we were doing this from scratch then we could lay down some hard/fast rules about things apps aren't supposed to do and how apps are supposed to respond to those exception cases. Unfortunately we don't have that luxury here. Devin -- Devin J. Heitmueller - Kernel Labs http://www.kernellabs.com -- To unsubscribe from this list: send the line unsubscribe linux-media in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [alsa-devel] [PATCH v2 5/6] sound/usb: pcm changes to use media token api
On 10/16/2014 04:48 PM, Takashi Iwai wrote:
At Thu, 16 Oct 2014 08:39:14 -0600,
Shuah Khan wrote:
On 10/16/2014 08:16 AM, Takashi Iwai wrote:
At Thu, 16 Oct 2014 08:10:52 -0600,
Shuah Khan wrote:
On 10/16/2014 08:01 AM, Takashi Iwai wrote:
At Thu, 16 Oct 2014 07:10:37 -0600,
Shuah Khan wrote:
On 10/16/2014 06:00 AM, Lars-Peter Clausen wrote:
On 10/14/2014 04:58 PM, Shuah Khan wrote:
[...]
switch (cmd) {
case SNDRV_PCM_TRIGGER_START:
+err = media_get_audio_tkn(subs-dev-dev);
+if (err == -EBUSY) {
+dev_info(subs-dev-dev, %s device is busy\n,
+__func__);
In my opinion this should not dev_info() as this is out of band error
signaling and also as the potential to spam the log. The userspace
application is already properly notified by the return code.
Yes it has the potential to flood the dmesg especially with alsa,
I will remove the dev_info().
Yes. And, I think doing this in the trigger isn't the best.
Why not in open close?
My first cut of this change was in open and close. I saw pulseaudio
application go into this loop trying to open the device. To avoid
such problems, I went with trigger stat and stop. That made all the
pulseaudio continues attempts to open problems go away.
But now starting the stream gives the error, and PA would loop it
again, no?
Also, is this token restriction needed only for PCM? No mixer or
other controls?
snd_pcm_ops are the only ones media drivers implement and use. So
I don't think mixer is needed. If it is needed, it is not to hard
to add for that case.
Well, then I wonder what resource does actually conflict with
usb-audio and media drivers at all...?
audio for dvb/v4l apps gets disrupted when audio app starts. For
example, dvb or v4l app tuned to a channel, and when an audio app
starts. audio path needs protected to avoid conflicts between
digital and analog applications as well.
OK, then concentrating on only PCM is fine.
But, I'm still not convinced about doing the token management in the
trigger. The reason -EBUSY doesn't work is that it's the very same
error code when a PCM device is blocked by other processes. And
-EAGAIN is interpreted by PCM core to -EBUSY for historical reasons.
How applications (e.g. PA) should behave if the token get fails?
Shouldn't it retry or totally give up?
Quite often media apps open the alsa device at the start and then switch
between TV, radio or DVB mode. If the alsa device would claim the tuner
just by being opened (as opposed to actually using the tuner, which happens
when you start streaming), then that would make it impossible for the
application to switch tuner mode. In general you want to avoid that open()
will start configuring hardware since that can quite often be slow. Tuner
configuration in particular can be slow since several common tuners need
to load firmware over i2c. You only want to do that when it is really needed,
and not when some application (udev!) opens the device just to examine what
sort of device it is.
So claiming the tuner in the trigger seems to be the right place. If
returning EBUSY is a poor error code for alsa, then we can use something else
for that. EACCES perhaps?
Regards,
Hans
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Re: [alsa-devel] [PATCH v2 5/6] sound/usb: pcm changes to use media token api
At Tue, 21 Oct 2014 17:42:51 +0200,
Hans Verkuil wrote:
On 10/16/2014 04:48 PM, Takashi Iwai wrote:
At Thu, 16 Oct 2014 08:39:14 -0600,
Shuah Khan wrote:
On 10/16/2014 08:16 AM, Takashi Iwai wrote:
At Thu, 16 Oct 2014 08:10:52 -0600,
Shuah Khan wrote:
On 10/16/2014 08:01 AM, Takashi Iwai wrote:
At Thu, 16 Oct 2014 07:10:37 -0600,
Shuah Khan wrote:
On 10/16/2014 06:00 AM, Lars-Peter Clausen wrote:
On 10/14/2014 04:58 PM, Shuah Khan wrote:
[...]
switch (cmd) {
case SNDRV_PCM_TRIGGER_START:
+err = media_get_audio_tkn(subs-dev-dev);
+if (err == -EBUSY) {
+dev_info(subs-dev-dev, %s device is busy\n,
+__func__);
In my opinion this should not dev_info() as this is out of band error
signaling and also as the potential to spam the log. The userspace
application is already properly notified by the return code.
Yes it has the potential to flood the dmesg especially with alsa,
I will remove the dev_info().
Yes. And, I think doing this in the trigger isn't the best.
Why not in open close?
My first cut of this change was in open and close. I saw pulseaudio
application go into this loop trying to open the device. To avoid
such problems, I went with trigger stat and stop. That made all the
pulseaudio continues attempts to open problems go away.
But now starting the stream gives the error, and PA would loop it
again, no?
Also, is this token restriction needed only for PCM? No mixer or
other controls?
snd_pcm_ops are the only ones media drivers implement and use. So
I don't think mixer is needed. If it is needed, it is not to hard
to add for that case.
Well, then I wonder what resource does actually conflict with
usb-audio and media drivers at all...?
audio for dvb/v4l apps gets disrupted when audio app starts. For
example, dvb or v4l app tuned to a channel, and when an audio app
starts. audio path needs protected to avoid conflicts between
digital and analog applications as well.
OK, then concentrating on only PCM is fine.
But, I'm still not convinced about doing the token management in the
trigger. The reason -EBUSY doesn't work is that it's the very same
error code when a PCM device is blocked by other processes. And
-EAGAIN is interpreted by PCM core to -EBUSY for historical reasons.
How applications (e.g. PA) should behave if the token get fails?
Shouldn't it retry or totally give up?
Quite often media apps open the alsa device at the start and then switch
between TV, radio or DVB mode. If the alsa device would claim the tuner
just by being opened (as opposed to actually using the tuner, which happens
when you start streaming),
What about parameter changes? The sound devices have to be configured
before using. Don't they influence on others at all, i.e. you can
change the PCM sample rate etc during TV, radio or DVB is running?
then that would make it impossible for the
application to switch tuner mode. In general you want to avoid that open()
will start configuring hardware since that can quite often be slow. Tuner
configuration in particular can be slow since several common tuners need
to load firmware over i2c. You only want to do that when it is really needed,
and not when some application (udev!) opens the device just to examine what
sort of device it is.
But most apps close the device soon after that, no?
Which programs keep the PCM device (not the control) opened without
actually using?
So claiming the tuner in the trigger seems to be the right place. If
returning EBUSY is a poor error code for alsa, then we can use something else
for that. EACCES perhaps?
Sorry, I'm not convinced by that. If the device has to be controlled
exclusively, the right position is the open/close. Otherwise, the
program cannot know when it becomes inaccessible out of sudden during
its operation.
Takashi
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Re: [alsa-devel] [PATCH v2 5/6] sound/usb: pcm changes to use media token api
Sorry, I'm not convinced by that. If the device has to be controlled exclusively, the right position is the open/close. Otherwise, the program cannot know when it becomes inaccessible out of sudden during its operation. I can say that I've definitely seen cases where if you configure a device as the default capture device in PulseAudio, then pulse will continue to capture from it even if you're not actively capturing the audio from pulse. I only spotted this because I had a USB analyzer on the device and was dumbfounded when the ISOC packets kept arriving even after I had closed VLC. Devin -- Devin J. Heitmueller - Kernel Labs http://www.kernellabs.com -- To unsubscribe from this list: send the line unsubscribe linux-media in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [alsa-devel] [PATCH v2 5/6] sound/usb: pcm changes to use media token api
At Tue, 21 Oct 2014 12:08:59 -0400, Devin Heitmueller wrote: Sorry, I'm not convinced by that. If the device has to be controlled exclusively, the right position is the open/close. Otherwise, the program cannot know when it becomes inaccessible out of sudden during its operation. I can say that I've definitely seen cases where if you configure a device as the default capture device in PulseAudio, then pulse will continue to capture from it even if you're not actively capturing the audio from pulse. I only spotted this because I had a USB analyzer on the device and was dumbfounded when the ISOC packets kept arriving even after I had closed VLC. You might have had an input monitor active in some PA apps? PA shouldn't do it as default. If it does unintentionally, you should report it to PA guys. Takashi -- To unsubscribe from this list: send the line unsubscribe linux-media in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [alsa-devel] [PATCH v2 5/6] sound/usb: pcm changes to use media token api
On 10/21/2014 10:05 AM, Takashi Iwai wrote: At Tue, 21 Oct 2014 17:42:51 +0200, Hans Verkuil wrote: Quite often media apps open the alsa device at the start and then switch between TV, radio or DVB mode. If the alsa device would claim the tuner just by being opened (as opposed to actually using the tuner, which happens when you start streaming), What about parameter changes? The sound devices have to be configured before using. Don't they influence on others at all, i.e. you can change the PCM sample rate etc during TV, radio or DVB is running? Yes. kaffeine uses snd_usb_capture_ops ioctl - snd_pcm_lib_ioctl Other v4l and vlc (dvb) uses open/close as well as trigger start and stop. trigger start/stop is done by a special audio thread in some cases. open/close happens from the main thread. then that would make it impossible for the application to switch tuner mode. In general you want to avoid that open() will start configuring hardware since that can quite often be slow. Tuner configuration in particular can be slow since several common tuners need to load firmware over i2c. You only want to do that when it is really needed, and not when some application (udev!) opens the device just to examine what sort of device it is. But most apps close the device soon after that, no? Which programs keep the PCM device (not the control) opened without actually using? So claiming the tuner in the trigger seems to be the right place. If returning EBUSY is a poor error code for alsa, then we can use something else for that. EACCES perhaps? Sorry, I'm not convinced by that. If the device has to be controlled exclusively, the right position is the open/close. Otherwise, the program cannot know when it becomes inaccessible out of sudden during its operation. Let me share my test matrix for this patch series. Hans pointed out one test case I didn't know about as a result missed testing. Please see if any of the tests miss use-cases or break them: you can scroll down to the proposal at the end, if this is too much detail :) Digital active and analog starting testing: kaffeine running - v4l2-ctl --all - works - Changing channels works with the same token hold, even when frequency changes. Tested changing channels that force freq change. - vlc resource is busy with no disruption to kaffeine - xawtv - tuner busy when it tries to do ioctls that change tuner settings - snd_usb_pcm_open detects device is busy ( pcm open called from the same thread, trigger gets called from another thread ) - tvtime - tuner busy when it tries to do ioctls that change tuner settings with no disruption to kaffeine ( pcm open called from the same thread, trigger gets called from another thread ) - vlc - audio capture on WinTV HVR-950 - device is busy start vlc with no channels for this test - arecord to capture on WinTV HVR-950 - device busy vlc running vlc -v channels.xspf - v4l2-ctl --all - works - Changing channels works with the same token hold, even when frequency changes. Tested changing channels that force freq change. - kaffeine resource is busy with no disruption to vlc - xawtv - tuner busy when it tries to do ioctls that change tuner settings - snd_usb_pcm_open detects device is busy ( pcm open called from the same thread, trigger gets called from another thread ) - tvtime - tuner busy when it tries to do ioctls that change tuner settings with no disruption to kaffeine ( pcm open called from the same thread, trigger gets called from another thread ) - vlc - audio capture on WinTV HVR-950 - device is busy - arecord to capture on WinTV HVR-950 - device busy Analog active and start digital testing: xawtv -noalsa -c /dev/video1 - v4l2-ctl --all - works - start kaffeine - fails with device busy and no disruption - start vlc - fails with device busy and no disruption - tvtime - tuner busy when it tries to do ioctls that change tuner settings with no disruption to kaffeine - vlc - audio capture on WinTV HVR-950 - device is busy - arecord to capture on WinTV HVR-950 - device busy tvtime - v4l2-ctl --all - works - start kaffeine - fails with device busy and no disruption - start vlc - fails with device busy and no disruption - xawtv - tuner busy when it tries to do ioctls that change tuner settings with no disruption to kaffeine - vlc - audio capture on WinTV HVR-950 - device is busy - arecord to capture on WinTV HVR-950 - device busy The following audio/video start/stop combination tests: ( used arecord as well to test these cases, arecord ) - tvtime start/vlc start/vlc stop/tvtime stop no disruption to tvtime - tvtime start/vlc start/tvtie stop/vlc stop One tvtime stops, could trigger capture manually - vlc start/tvtime start/tvtime stop/vlc stop vlc audio capture continues, tvtime detect tuner busy - vlc start/tvtime start/vlc stop/tvtime start when vlc stops, tvtime could open the tuner device Repeated the above with kaffeine and vlc and
Re: [alsa-devel] [PATCH v2 5/6] sound/usb: pcm changes to use media token api
At Sat, 18 Oct 2014 20:49:58 +0200,
Mauro Carvalho Chehab wrote:
Em Thu, 16 Oct 2014 08:59:29 -0600
Shuah Khan shua...@osg.samsung.com escreveu:
On 10/16/2014 08:48 AM, Takashi Iwai wrote:
At Thu, 16 Oct 2014 08:39:14 -0600,
Shuah Khan wrote:
On 10/16/2014 08:16 AM, Takashi Iwai wrote:
At Thu, 16 Oct 2014 08:10:52 -0600,
Shuah Khan wrote:
On 10/16/2014 08:01 AM, Takashi Iwai wrote:
At Thu, 16 Oct 2014 07:10:37 -0600,
Shuah Khan wrote:
On 10/16/2014 06:00 AM, Lars-Peter Clausen wrote:
On 10/14/2014 04:58 PM, Shuah Khan wrote:
[...]
switch (cmd) {
case SNDRV_PCM_TRIGGER_START:
+err = media_get_audio_tkn(subs-dev-dev);
+if (err == -EBUSY) {
+dev_info(subs-dev-dev, %s device is busy\n,
+__func__);
In my opinion this should not dev_info() as this is out of band
error
signaling and also as the potential to spam the log. The userspace
application is already properly notified by the return code.
Yes it has the potential to flood the dmesg especially with alsa,
I will remove the dev_info().
Yes. And, I think doing this in the trigger isn't the best.
Why not in open close?
My first cut of this change was in open and close. I saw pulseaudio
application go into this loop trying to open the device. To avoid
such problems, I went with trigger stat and stop. That made all the
pulseaudio continues attempts to open problems go away.
But now starting the stream gives the error, and PA would loop it
again, no?
Also, is this token restriction needed only for PCM? No mixer or
other controls?
snd_pcm_ops are the only ones media drivers implement and use. So
I don't think mixer is needed. If it is needed, it is not to hard
to add for that case.
Well, then I wonder what resource does actually conflict with
usb-audio and media drivers at all...?
audio for dvb/v4l apps gets disrupted when audio app starts. For
example, dvb or v4l app tuned to a channel, and when an audio app
starts. audio path needs protected to avoid conflicts between
digital and analog applications as well.
OK, then concentrating on only PCM is fine.
But, I'm still not convinced about doing the token management in the
trigger. The reason -EBUSY doesn't work is that it's the very same
error code when a PCM device is blocked by other processes. And
-EAGAIN is interpreted by PCM core to -EBUSY for historical reasons.
ah. ok your recommendation is to go with open and close.
Mauro has some reservations with holding at open when I discussed
my observations with pulseaudio when I was holding token in open
instead of trigger start. Maybe he can chime with his concerns.
I think his concern was breaking applications if token is held in
open().
Yes. My concern is that PA has weird behaviors, and it tries to open and
keep opened all audio devices.
PA usually closes the PCM devices when unused. If it doesn't, it must
be a bug.
Takashi
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Re: [alsa-devel] [PATCH v2 5/6] sound/usb: pcm changes to use media token api
Em Thu, 16 Oct 2014 08:59:29 -0600
Shuah Khan shua...@osg.samsung.com escreveu:
On 10/16/2014 08:48 AM, Takashi Iwai wrote:
At Thu, 16 Oct 2014 08:39:14 -0600,
Shuah Khan wrote:
On 10/16/2014 08:16 AM, Takashi Iwai wrote:
At Thu, 16 Oct 2014 08:10:52 -0600,
Shuah Khan wrote:
On 10/16/2014 08:01 AM, Takashi Iwai wrote:
At Thu, 16 Oct 2014 07:10:37 -0600,
Shuah Khan wrote:
On 10/16/2014 06:00 AM, Lars-Peter Clausen wrote:
On 10/14/2014 04:58 PM, Shuah Khan wrote:
[...]
switch (cmd) {
case SNDRV_PCM_TRIGGER_START:
+err = media_get_audio_tkn(subs-dev-dev);
+if (err == -EBUSY) {
+dev_info(subs-dev-dev, %s device is busy\n,
+__func__);
In my opinion this should not dev_info() as this is out of band error
signaling and also as the potential to spam the log. The userspace
application is already properly notified by the return code.
Yes it has the potential to flood the dmesg especially with alsa,
I will remove the dev_info().
Yes. And, I think doing this in the trigger isn't the best.
Why not in open close?
My first cut of this change was in open and close. I saw pulseaudio
application go into this loop trying to open the device. To avoid
such problems, I went with trigger stat and stop. That made all the
pulseaudio continues attempts to open problems go away.
But now starting the stream gives the error, and PA would loop it
again, no?
Also, is this token restriction needed only for PCM? No mixer or
other controls?
snd_pcm_ops are the only ones media drivers implement and use. So
I don't think mixer is needed. If it is needed, it is not to hard
to add for that case.
Well, then I wonder what resource does actually conflict with
usb-audio and media drivers at all...?
audio for dvb/v4l apps gets disrupted when audio app starts. For
example, dvb or v4l app tuned to a channel, and when an audio app
starts. audio path needs protected to avoid conflicts between
digital and analog applications as well.
OK, then concentrating on only PCM is fine.
But, I'm still not convinced about doing the token management in the
trigger. The reason -EBUSY doesn't work is that it's the very same
error code when a PCM device is blocked by other processes. And
-EAGAIN is interpreted by PCM core to -EBUSY for historical reasons.
ah. ok your recommendation is to go with open and close.
Mauro has some reservations with holding at open when I discussed
my observations with pulseaudio when I was holding token in open
instead of trigger start. Maybe he can chime with his concerns.
I think his concern was breaking applications if token is held in
open().
Yes. My concern is that PA has weird behaviors, and it tries to open and
keep opened all audio devices. Is there a way for avoiding it to keep doing
it for V4L devices?
Based on what you are seeing trigger could be worse.
How applications (e.g. PA) should behave if the token get fails?
Shouldn't it retry or totally give up?
It would be up to the application I would think. I see that arecord
quits right away when it finds the device busy. pluseaudio on the other
hand appears to retry. I downloaded pulseaudio sources to understand
what it is doing, however I didn't get too far. The way it does audio
handling is complex for me to follow without spending a lot of time.
thanks,
-- Shuah
--
Cheers,
Mauro
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Re: [alsa-devel] [PATCH v2 5/6] sound/usb: pcm changes to use media token api
On 10/14/2014 04:58 PM, Shuah Khan wrote:
[...]
switch (cmd) {
case SNDRV_PCM_TRIGGER_START:
+ err = media_get_audio_tkn(subs-dev-dev);
+ if (err == -EBUSY) {
+ dev_info(subs-dev-dev, %s device is busy\n,
+ __func__);
In my opinion this should not dev_info() as this is out of band error
signaling and also as the potential to spam the log. The userspace
application is already properly notified by the return code.
+ return err;
+ }
err = start_endpoints(subs, false);
if (err 0)
return err;
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Re: [alsa-devel] [PATCH v2 5/6] sound/usb: pcm changes to use media token api
On 10/16/2014 06:00 AM, Lars-Peter Clausen wrote:
On 10/14/2014 04:58 PM, Shuah Khan wrote:
[...]
switch (cmd) {
case SNDRV_PCM_TRIGGER_START:
+err = media_get_audio_tkn(subs-dev-dev);
+if (err == -EBUSY) {
+dev_info(subs-dev-dev, %s device is busy\n,
+__func__);
In my opinion this should not dev_info() as this is out of band error
signaling and also as the potential to spam the log. The userspace
application is already properly notified by the return code.
Yes it has the potential to flood the dmesg especially with alsa,
I will remove the dev_info().
thanks,
-- Shuah
--
Shuah Khan
Sr. Linux Kernel Developer
Samsung Research America (Silicon Valley)
shua...@osg.samsung.com | (970) 217-8978
--
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More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [alsa-devel] [PATCH v2 5/6] sound/usb: pcm changes to use media token api
At Thu, 16 Oct 2014 07:10:37 -0600,
Shuah Khan wrote:
On 10/16/2014 06:00 AM, Lars-Peter Clausen wrote:
On 10/14/2014 04:58 PM, Shuah Khan wrote:
[...]
switch (cmd) {
case SNDRV_PCM_TRIGGER_START:
+err = media_get_audio_tkn(subs-dev-dev);
+if (err == -EBUSY) {
+dev_info(subs-dev-dev, %s device is busy\n,
+__func__);
In my opinion this should not dev_info() as this is out of band error
signaling and also as the potential to spam the log. The userspace
application is already properly notified by the return code.
Yes it has the potential to flood the dmesg especially with alsa,
I will remove the dev_info().
Yes. And, I think doing this in the trigger isn't the best.
Why not in open close?
Also, is this token restriction needed only for PCM? No mixer or
other controls?
Takashi
--
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the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [alsa-devel] [PATCH v2 5/6] sound/usb: pcm changes to use media token api
On 10/16/2014 08:01 AM, Takashi Iwai wrote:
At Thu, 16 Oct 2014 07:10:37 -0600,
Shuah Khan wrote:
On 10/16/2014 06:00 AM, Lars-Peter Clausen wrote:
On 10/14/2014 04:58 PM, Shuah Khan wrote:
[...]
switch (cmd) {
case SNDRV_PCM_TRIGGER_START:
+err = media_get_audio_tkn(subs-dev-dev);
+if (err == -EBUSY) {
+dev_info(subs-dev-dev, %s device is busy\n,
+__func__);
In my opinion this should not dev_info() as this is out of band error
signaling and also as the potential to spam the log. The userspace
application is already properly notified by the return code.
Yes it has the potential to flood the dmesg especially with alsa,
I will remove the dev_info().
Yes. And, I think doing this in the trigger isn't the best.
Why not in open close?
My first cut of this change was in open and close. I saw pulseaudio
application go into this loop trying to open the device. To avoid
such problems, I went with trigger stat and stop. That made all the
pulseaudio continues attempts to open problems go away.
Also, is this token restriction needed only for PCM? No mixer or
other controls?
snd_pcm_ops are the only ones media drivers implement and use. So
I don't think mixer is needed. If it is needed, it is not to hard
to add for that case.
thanks,
-- Shuah
--
Shuah Khan
Sr. Linux Kernel Developer
Samsung Research America (Silicon Valley)
shua...@osg.samsung.com | (970) 217-8978
--
To unsubscribe from this list: send the line unsubscribe linux-media in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [alsa-devel] [PATCH v2 5/6] sound/usb: pcm changes to use media token api
At Thu, 16 Oct 2014 08:10:52 -0600,
Shuah Khan wrote:
On 10/16/2014 08:01 AM, Takashi Iwai wrote:
At Thu, 16 Oct 2014 07:10:37 -0600,
Shuah Khan wrote:
On 10/16/2014 06:00 AM, Lars-Peter Clausen wrote:
On 10/14/2014 04:58 PM, Shuah Khan wrote:
[...]
switch (cmd) {
case SNDRV_PCM_TRIGGER_START:
+err = media_get_audio_tkn(subs-dev-dev);
+if (err == -EBUSY) {
+dev_info(subs-dev-dev, %s device is busy\n,
+__func__);
In my opinion this should not dev_info() as this is out of band error
signaling and also as the potential to spam the log. The userspace
application is already properly notified by the return code.
Yes it has the potential to flood the dmesg especially with alsa,
I will remove the dev_info().
Yes. And, I think doing this in the trigger isn't the best.
Why not in open close?
My first cut of this change was in open and close. I saw pulseaudio
application go into this loop trying to open the device. To avoid
such problems, I went with trigger stat and stop. That made all the
pulseaudio continues attempts to open problems go away.
But now starting the stream gives the error, and PA would loop it
again, no?
Also, is this token restriction needed only for PCM? No mixer or
other controls?
snd_pcm_ops are the only ones media drivers implement and use. So
I don't think mixer is needed. If it is needed, it is not to hard
to add for that case.
Well, then I wonder what resource does actually conflict with
usb-audio and media drivers at all...?
Takashi
--
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the body of a message to majord...@vger.kernel.org
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Re: [alsa-devel] [PATCH v2 5/6] sound/usb: pcm changes to use media token api
On 10/16/2014 08:16 AM, Takashi Iwai wrote:
At Thu, 16 Oct 2014 08:10:52 -0600,
Shuah Khan wrote:
On 10/16/2014 08:01 AM, Takashi Iwai wrote:
At Thu, 16 Oct 2014 07:10:37 -0600,
Shuah Khan wrote:
On 10/16/2014 06:00 AM, Lars-Peter Clausen wrote:
On 10/14/2014 04:58 PM, Shuah Khan wrote:
[...]
switch (cmd) {
case SNDRV_PCM_TRIGGER_START:
+err = media_get_audio_tkn(subs-dev-dev);
+if (err == -EBUSY) {
+dev_info(subs-dev-dev, %s device is busy\n,
+__func__);
In my opinion this should not dev_info() as this is out of band error
signaling and also as the potential to spam the log. The userspace
application is already properly notified by the return code.
Yes it has the potential to flood the dmesg especially with alsa,
I will remove the dev_info().
Yes. And, I think doing this in the trigger isn't the best.
Why not in open close?
My first cut of this change was in open and close. I saw pulseaudio
application go into this loop trying to open the device. To avoid
such problems, I went with trigger stat and stop. That made all the
pulseaudio continues attempts to open problems go away.
But now starting the stream gives the error, and PA would loop it
again, no?
Also, is this token restriction needed only for PCM? No mixer or
other controls?
snd_pcm_ops are the only ones media drivers implement and use. So
I don't think mixer is needed. If it is needed, it is not to hard
to add for that case.
Well, then I wonder what resource does actually conflict with
usb-audio and media drivers at all...?
audio for dvb/v4l apps gets disrupted when audio app starts. For
example, dvb or v4l app tuned to a channel, and when an audio app
starts. audio path needs protected to avoid conflicts between
digital and analog applications as well.
-- Shuah
--
Shuah Khan
Sr. Linux Kernel Developer
Samsung Research America (Silicon Valley)
shua...@osg.samsung.com | (970) 217-8978
--
To unsubscribe from this list: send the line unsubscribe linux-media in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [alsa-devel] [PATCH v2 5/6] sound/usb: pcm changes to use media token api
At Thu, 16 Oct 2014 08:39:14 -0600,
Shuah Khan wrote:
On 10/16/2014 08:16 AM, Takashi Iwai wrote:
At Thu, 16 Oct 2014 08:10:52 -0600,
Shuah Khan wrote:
On 10/16/2014 08:01 AM, Takashi Iwai wrote:
At Thu, 16 Oct 2014 07:10:37 -0600,
Shuah Khan wrote:
On 10/16/2014 06:00 AM, Lars-Peter Clausen wrote:
On 10/14/2014 04:58 PM, Shuah Khan wrote:
[...]
switch (cmd) {
case SNDRV_PCM_TRIGGER_START:
+err = media_get_audio_tkn(subs-dev-dev);
+if (err == -EBUSY) {
+dev_info(subs-dev-dev, %s device is busy\n,
+__func__);
In my opinion this should not dev_info() as this is out of band error
signaling and also as the potential to spam the log. The userspace
application is already properly notified by the return code.
Yes it has the potential to flood the dmesg especially with alsa,
I will remove the dev_info().
Yes. And, I think doing this in the trigger isn't the best.
Why not in open close?
My first cut of this change was in open and close. I saw pulseaudio
application go into this loop trying to open the device. To avoid
such problems, I went with trigger stat and stop. That made all the
pulseaudio continues attempts to open problems go away.
But now starting the stream gives the error, and PA would loop it
again, no?
Also, is this token restriction needed only for PCM? No mixer or
other controls?
snd_pcm_ops are the only ones media drivers implement and use. So
I don't think mixer is needed. If it is needed, it is not to hard
to add for that case.
Well, then I wonder what resource does actually conflict with
usb-audio and media drivers at all...?
audio for dvb/v4l apps gets disrupted when audio app starts. For
example, dvb or v4l app tuned to a channel, and when an audio app
starts. audio path needs protected to avoid conflicts between
digital and analog applications as well.
OK, then concentrating on only PCM is fine.
But, I'm still not convinced about doing the token management in the
trigger. The reason -EBUSY doesn't work is that it's the very same
error code when a PCM device is blocked by other processes. And
-EAGAIN is interpreted by PCM core to -EBUSY for historical reasons.
How applications (e.g. PA) should behave if the token get fails?
Shouldn't it retry or totally give up?
Takashi
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Re: [alsa-devel] [PATCH v2 5/6] sound/usb: pcm changes to use media token api
On 10/16/2014 08:48 AM, Takashi Iwai wrote:
At Thu, 16 Oct 2014 08:39:14 -0600,
Shuah Khan wrote:
On 10/16/2014 08:16 AM, Takashi Iwai wrote:
At Thu, 16 Oct 2014 08:10:52 -0600,
Shuah Khan wrote:
On 10/16/2014 08:01 AM, Takashi Iwai wrote:
At Thu, 16 Oct 2014 07:10:37 -0600,
Shuah Khan wrote:
On 10/16/2014 06:00 AM, Lars-Peter Clausen wrote:
On 10/14/2014 04:58 PM, Shuah Khan wrote:
[...]
switch (cmd) {
case SNDRV_PCM_TRIGGER_START:
+err = media_get_audio_tkn(subs-dev-dev);
+if (err == -EBUSY) {
+dev_info(subs-dev-dev, %s device is busy\n,
+__func__);
In my opinion this should not dev_info() as this is out of band error
signaling and also as the potential to spam the log. The userspace
application is already properly notified by the return code.
Yes it has the potential to flood the dmesg especially with alsa,
I will remove the dev_info().
Yes. And, I think doing this in the trigger isn't the best.
Why not in open close?
My first cut of this change was in open and close. I saw pulseaudio
application go into this loop trying to open the device. To avoid
such problems, I went with trigger stat and stop. That made all the
pulseaudio continues attempts to open problems go away.
But now starting the stream gives the error, and PA would loop it
again, no?
Also, is this token restriction needed only for PCM? No mixer or
other controls?
snd_pcm_ops are the only ones media drivers implement and use. So
I don't think mixer is needed. If it is needed, it is not to hard
to add for that case.
Well, then I wonder what resource does actually conflict with
usb-audio and media drivers at all...?
audio for dvb/v4l apps gets disrupted when audio app starts. For
example, dvb or v4l app tuned to a channel, and when an audio app
starts. audio path needs protected to avoid conflicts between
digital and analog applications as well.
OK, then concentrating on only PCM is fine.
But, I'm still not convinced about doing the token management in the
trigger. The reason -EBUSY doesn't work is that it's the very same
error code when a PCM device is blocked by other processes. And
-EAGAIN is interpreted by PCM core to -EBUSY for historical reasons.
ah. ok your recommendation is to go with open and close.
Mauro has some reservations with holding at open when I discussed
my observations with pulseaudio when I was holding token in open
instead of trigger start. Maybe he can chime with his concerns.
I think his concern was breaking applications if token is held in
open().
Based on what you are seeing trigger could be worse.
How applications (e.g. PA) should behave if the token get fails?
Shouldn't it retry or totally give up?
It would be up to the application I would think. I see that arecord
quits right away when it finds the device busy. pluseaudio on the other
hand appears to retry. I downloaded pulseaudio sources to understand
what it is doing, however I didn't get too far. The way it does audio
handling is complex for me to follow without spending a lot of time.
thanks,
-- Shuah
--
Shuah Khan
Sr. Linux Kernel Developer
Samsung Research America (Silicon Valley)
shua...@osg.samsung.com | (970) 217-8978
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[PATCH v2 5/6] sound/usb: pcm changes to use media token api
Change snd_usb_capture_ops trigger to hold audio token prior
starting endpoints for SNDRV_PCM_TRIGGER_START request and
release after stopping endpoints for SNDRV_PCM_TRIGGER_STOP
request. Audio token is released from snd_usb_capture_ops
close interface to cover the case where an application exits
without stopping capture. Audio token get request will succeed
if it is free or when a media application with the same task
pid or task gid makes the request. This covers the cases when
a media application first hold the tuner nd audio token and
then requests SNDRV_PCM_TRIGGER_START either from the same
thread or a another thread in the same process group.
Signed-off-by: Shuah Khan shua...@osg.samsung.com
---
sound/usb/pcm.c |9 +
1 file changed, 9 insertions(+)
diff --git a/sound/usb/pcm.c b/sound/usb/pcm.c
index c62a165..d23abeb 100644
--- a/sound/usb/pcm.c
+++ b/sound/usb/pcm.c
@@ -21,6 +21,7 @@
#include linux/usb.h
#include linux/usb/audio.h
#include linux/usb/audio-v2.h
+#include linux/media_tknres.h
#include sound/core.h
#include sound/pcm.h
@@ -1220,6 +1221,7 @@ static int snd_usb_pcm_close(struct snd_pcm_substream
*substream, int direction)
subs-pcm_substream = NULL;
snd_usb_autosuspend(subs-stream-chip);
+ media_put_audio_tkn(subs-dev-dev);
return 0;
}
@@ -1573,6 +1575,12 @@ static int snd_usb_substream_capture_trigger(struct
snd_pcm_substream *substream
switch (cmd) {
case SNDRV_PCM_TRIGGER_START:
+ err = media_get_audio_tkn(subs-dev-dev);
+ if (err == -EBUSY) {
+ dev_info(subs-dev-dev, %s device is busy\n,
+ __func__);
+ return err;
+ }
err = start_endpoints(subs, false);
if (err 0)
return err;
@@ -1583,6 +1591,7 @@ static int snd_usb_substream_capture_trigger(struct
snd_pcm_substream *substream
case SNDRV_PCM_TRIGGER_STOP:
stop_endpoints(subs, false);
subs-running = 0;
+ media_put_audio_tkn(subs-dev-dev);
return 0;
case SNDRV_PCM_TRIGGER_PAUSE_PUSH:
subs-data_endpoint-retire_data_urb = NULL;
--
1.7.10.4
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