Re: CDF meeting @FOSDEM report
On Wed, Feb 6, 2013 at 6:11 AM, Tomi Valkeinen tomi.valkei...@ti.com wrote: Hi, On 2013-02-06 00:27, Laurent Pinchart wrote: Hello, We've hosted a CDF meeting at the FOSDEM on Sunday morning. Here's a summary of the discussions. Thanks for the summary. I've been on a longish leave, and just got back, so I haven't read the recent CDF discussions on lists yet. I thought I'll start by replying to this summary first =). 0. Abbreviations DBI - Display Bus Interface, a parallel video control and data bus that transmits data using parallel data, read/write, chip select and address signals, similarly to 8051-style microcontroller parallel busses. This is a mixed video control and data bus. DPI - Display Pixel Interface, a parallel video data bus that transmits data using parallel data, h/v sync and clock signals. This is a video data bus only. DSI - Display Serial Interface, a serial video control and data bus that transmits data using one or more differential serial lines. This is a mixed video control and data bus. In case you'll re-use these abbrevs in later posts, I think it would be good to mention that DPI is a one-way bus, whereas DBI and DSI are two-way (perhaps that's implicit with control bus, though). 1. Goals The meeting started with a brief discussion about the CDF goals. Tomi Valkeinin and Tomasz Figa have sent RFC patches to show their views of what CDF could/should be. Many others have provided very valuable feedback. Given the early development stage propositions were sometimes contradictory, and focused on different areas of interest. We have thus started the meeting with a discussion about what CDF should try to achieve, and what it shouldn't. CDF has two main purposes. The original goal was to support display panels in a platform- and subsystem-independent way. While mostly useful for embedded systems, the emergence of platforms such as Intel Medfield and ARM-based PCs that blends the embedded and PC worlds makes panel support useful for the PC world as well. The second purpose is to provide a cross-subsystem interface to support video encoders. The idea originally came from a generalisation of the original RFC that supported panels only. While encoder support is considered as lower priority than display panel support by developers focussed on display controller driver (Intel, Renesas, ST Ericsson, TI), companies that produce video encoders (Analog Devices, and likely others) don't share that point of view and would like to provide a single encoder driver that can be used in both KMS and V4L2 drivers. What is an encoder? Something that takes a video signal in, and lets the CPU store the received data to memory? Isn't that a decoder? Or do you mean something that takes a video signal in, and outputs a video signal in another format? (transcoder?) In KMS parlance, we have two objects a crtc and an encoder. A crtc reads data from memory and produces a data stream with display timing. The encoder then takes that datastream and timing from the crtc and converts it some sort of physical signal (LVDS, TMDS, DP, etc.). It's not always a perfect match to the hardware. For example a lot of GPUs have a DVO encoder which feeds a secondary encoder like an sil164 DVO to TMDS encoder. Alex -- 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: CDF meeting @FOSDEM report
On 2013-02-06 16:44, Alex Deucher wrote: On Wed, Feb 6, 2013 at 6:11 AM, Tomi Valkeinen tomi.valkei...@ti.com wrote: What is an encoder? Something that takes a video signal in, and lets the CPU store the received data to memory? Isn't that a decoder? Or do you mean something that takes a video signal in, and outputs a video signal in another format? (transcoder?) In KMS parlance, we have two objects a crtc and an encoder. A crtc reads data from memory and produces a data stream with display timing. The encoder then takes that datastream and timing from the crtc and converts it some sort of physical signal (LVDS, TMDS, DP, etc.). It's Isn't the video stream between CRTC and encoder just as physical, it just happens to be inside the GPU? This is the case for OMAP, at least, where DISPC could be considered CRTC, and DSI/HDMI/etc could be considered encoder. The stream between DISPC and DSI/HDMI is plain parallel RGB signal. The video stream could as well be outside OMAP. not always a perfect match to the hardware. For example a lot of GPUs have a DVO encoder which feeds a secondary encoder like an sil164 DVO to TMDS encoder. Right. I think mapping the DRM entities to CDF ones is one of the bigger question marks we have with CDF. While I'm no expert on DRM, I think we have the following options: 1. Force DRM's model to CDF, meaning one encoder. 2. Extend DRM to support multiple encoders in a chain. 3. Support multiple encoders in a chain in CDF, but somehow map them to a single encoder in DRM side. I really dislike the first option, as it would severely limit where CDF can be used, or would force you to write some kind of combined drivers, so that you can have one encoder driver running multiple encoder devices. Tomi signature.asc Description: OpenPGP digital signature
Re: [Linaro-mm-sig] CDF meeting @FOSDEM report
On Wed, Feb 6, 2013 at 4:00 PM, Tomi Valkeinen tomi.valkei...@ti.com wrote: not always a perfect match to the hardware. For example a lot of GPUs have a DVO encoder which feeds a secondary encoder like an sil164 DVO to TMDS encoder. Right. I think mapping the DRM entities to CDF ones is one of the bigger question marks we have with CDF. While I'm no expert on DRM, I think we have the following options: 1. Force DRM's model to CDF, meaning one encoder. 2. Extend DRM to support multiple encoders in a chain. 3. Support multiple encoders in a chain in CDF, but somehow map them to a single encoder in DRM side. 4. Ignore drm kms encoders. They are only exposed to userspace as a means for userspace to discover very simple constraints, e.g. 1 encoder connected to 2 outputs means you can only use one of the outputs at the same time. They are completely irrelevant for the actual modeset interface exposed to drivers, so you could create a fake kms encoder for each connector you expose through kms. The crtc helpers use the encoders as a real entity, and if you opt to use the crtc helpers to implement the modeset sequence in your driver it makes sense to map them to some real piece of hw. But you can essentially pick any transcoder in your crtc - final output chain for this. Generic userspace needs to be able to cope with a failed modeset due to arbitrary reasons anyway, so can't presume that simply because the currently exposed constraints are fulfilled it'll work. I really dislike the first option, as it would severely limit where CDF can be used, or would force you to write some kind of combined drivers, so that you can have one encoder driver running multiple encoder devices. Imo CDF and drm encoders don't really have that much to do with each another, it should just be a driver implementation detail. Of course, if common patterns emerge we could extract them somehow. E.g. if many drivers end up exposing the CDF transcoder chain as a drm encoder using the crtc helpers, we could add some library functions to make that simpler. Another conclusion (at least from my pov) from the fosdem discussion is that we should separate the panel interface from the actual control/pixel data buses. That should give us more flexibility for insane hw and also directly exposing properties and knobs to the userspace interface from e.g. dsi transcoders. So I don't think we'll end up with _the_ canonical CDF sink interface anyway. -Daniel -- Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch -- 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
