On 01/12/2018 05:30 PM, Ville Syrjälä wrote:
> On Fri, Jan 12, 2018 at 05:19:44PM +0100, Hans Verkuil wrote:
>> Hi Ville,
>>
>> For some strange reason your email disappeared from the Cc list. Perhaps
>> it's the
>> ä that confuses something somewhere.
>>
>> So I'll just forward this directly to you.
>>
>> Can you please take a look? This patch series has been in limbo for too long.
>
> IIRC last I looked we still had some ragistration race to deal with.
> Was that fixed?
That was fixed in v5.
>
> Also I think we got stuck on leaving the zombie device lingering around
> when the display is disconnected. I couldn't understand why that is
> at all useful since you anyway remove the device eventually.
It's not a zombie device. If you disconnect and reconnect the display then the
application using the CEC device will see the display disappear and reappear
as expected.
It helps if you think of the normal situation (as is present in most ARM SoCs)
where CEC is integral to the HDMI transmitter. I.e. it is not functionality that
can be removed. So the cec device is always there and an application opens the
device and can use it, regardless of whether a display is connected or not.
If a display is detected, the EDID will be read and the CEC physical address is
set. The application is informed of that through an event and the CEC adapter
can be used. If the HPD disappears the physical address is reset to f.f.f.f and
again the application is informed. And in fact it still has to be able to use
the CEC adapter even if there is no HPD since some displays turn off the HPD
when
in standby, but CEC can still be used to power them up again.
Now consider a future Intel NUC with an HDMI connector on the backplane and
working DP CEC-Tunneling-over-AUX support (e.g. the Megachips MCDP2900): the
CEC support is always there (it's built in), but only becomes visible to the
kernel when you connect a display. You don't want the cec device to disappear
whenever you unplug the display, that makes no sense. Applications would
loose the CEC configuration and have to close and reopen (when it reappears)
the cec device for no good reason since it is built in.
The same situation is valid when using a USB-C to HDMI adapter: disconnecting
or reconnecting a display should not lead to the removal of the CEC device.
Only when an adapter with different CEC capabilities is detected is there a
need to actually unregister the CEC device.
All this is really a workaround of the fact that when the HPD disappears the
DP-to-HDMI adapter (either external or built-in) also disappears from the
topology, even though it is physically still there. If there was a way to
detect the adapter when there is no display connected, then this workaround
wouldn't be needed.
This situation is specific to DisplayPort, this is the only case where the
HDMI connector disappears in a puff of smoke when you disconnect the HDMI
cable, even though the actual physical connector is obviously still there.
Regards,
Hans
>
> Adding the lists back to cc so I don't have to repeat myself there...
>
>>
>> Regards,
>>
>> Hans
>>
>>
>> -------- Forwarded Message --------
>> Subject: Re: [PATCHv5 0/3] drm/i915: add DisplayPort CEC-Tunneling-over-AUX
>> support
>> Date: Tue, 9 Jan 2018 13:46:44 +0100
>> From: Hans Verkuil <hverk...@xs4all.nl>
>> To: linux-me...@vger.kernel.org
>> CC: Daniel Vetter <daniel.vet...@ffwll.ch>, Carlos Santa
>> <carlos.sa...@intel.com>, dri-devel@lists.freedesktop.org
>>
>> First of all a Happy New Year for all of you!
>>
>> And secondly: can this v5 patch series be reviewed/merged? It's been waiting
>> for that for a very long time now...
>>
>> Regards,
>>
>> Hans
>>
>> On 12/11/17 09:57, Hans Verkuil wrote:
>>> Ping again. Added a CC to Ville whom I inexplicably forgot to add when
>>> I sent the v5 patch series.
>>>
>>> Regards,
>>>
>>> Hans
>>>
>>> On 01/12/17 08:23, Hans Verkuil wrote:
>>>> Ping!
>>>>
>>>> I really like to get this in for 4.16 so I can move forward with hooking
>>>> this up for nouveau/amd.
>>>>
>>>> Regards,
>>>>
>>>> Hans
>>>>
>>>> On 11/20/2017 12:42 PM, Hans Verkuil wrote:
>>>>> This patch series adds support for the DisplayPort CEC-Tunneling-over-AUX
>>>>> feature. This patch series is based on the 4.14 mainline release but
>>>>> applies
>>>>> as well to drm-next.
>>>>>
>>>>> This patch series has been tested with my NUC7i5BNK, a Samsung USB-C to
>>>>> HDMI adapter and a Club 3D DisplayPort MST Hub + modified UpTab DP-to-HDMI
>>>>> adapter (where the CEC pin is wired up).
>>>>>
>>>>> Please note this comment at the start of drm_dp_cec.c:
>>>>>
>>>>> ----------------------------------------------------------------------
>>>>> Unfortunately it turns out that we have a chicken-and-egg situation
>>>>> here. Quite a few active (mini-)DP-to-HDMI or USB-C-to-HDMI adapters
>>>>> have a converter chip that supports CEC-Tunneling-over-AUX (usually the
>>>>> Parade PS176 or MegaChips MCDP2900), but they do not wire up the CEC pin,
>>>>> thus making CEC useless.
>>>>>
>>>>> Sadly there is no way for this driver to know this. What happens is
>>>>> that a /dev/cecX device is created that is isolated and unable to see
>>>>> any of the other CEC devices. Quite literally the CEC wire is cut
>>>>> (or in this case, never connected in the first place).
>>>>>
>>>>> I suspect that the reason so few adapters support this is that this
>>>>> tunneling protocol was never supported by any OS. So there was no
>>>>> easy way of testing it, and no incentive to correctly wire up the
>>>>> CEC pin.
>>>>>
>>>>> Hopefully by creating this driver it will be easier for vendors to
>>>>> finally fix their adapters and test the CEC functionality.
>>>>>
>>>>> I keep a list of known working adapters here:
>>>>>
>>>>> https://hverkuil.home.xs4all.nl/cec-status.txt
>>>>>
>>>>> Please mail me (hverk...@xs4all.nl) if you find an adapter that works
>>>>> and is not yet listed there.
>>>>>
>>>>> Note that the current implementation does not support CEC over an MST hub.
>>>>> As far as I can see there is no mechanism defined in the DisplayPort
>>>>> standard to transport CEC interrupts over an MST device. It might be
>>>>> possible to do this through polling, but I have not been able to get that
>>>>> to work.
>>>>> ----------------------------------------------------------------------
>>>>>
>>>>> I really hope that this work will provide an incentive for vendors to
>>>>> finally connect the CEC pin. It's a shame that there are so few adapters
>>>>> that work (I found only two USB-C to HDMI adapters that work, and no
>>>>> (mini-)DP to HDMI adapters at all).
>>>>>
>>>>> Hopefully if this gets merged there will be an incentive for vendors
>>>>> to make adapters where this actually works. It is a very nice feature
>>>>> for HTPC boxes.
>>>>>
>>>>> The main reason why this v5 is delayed by 2 months is due to the fact
>>>>> that I needed some dedicated time to investigate what happens when an
>>>>> MST hub is in use. It turns out that this is not working. There is no
>>>>> mechanism defined in the DisplayPort standard to transport the CEC
>>>>> interrupt back up the MST chain. I was actually able to send a CEC
>>>>> message but the interrupt that tells when the transmit finished is
>>>>> unavailable.
>>>>>
>>>>> I attempted to implement this via polling, but I got weird errors
>>>>> and was not able to read the DP_DEVICE_SERVICE_IRQ_VECTOR_ESI1
>>>>> register. I decided to give up on this for now and just disable CEC
>>>>> for DP-to-HDMI adapters after an MST hub. I plan to revisit this
>>>>> later since it would be neat to make this work as well. Although it
>>>>> might not be possible at all.
>>>>>
>>>>> If anyone is interested, work-in-progress for this is here:
>>>>>
>>>>> https://git.linuxtv.org/hverkuil/media_tree.git/log/?h=dp-cec-mst
>>>>>
>>>>> Note that I removed the Tested-by tag from Carlos Santa due to the
>>>>> almost complete rework of the third patch. Carlos, can you test this
>>>>> again?
>>>>>
>>>>> Regards,
>>>>>
>>>>> Hans
>>>>>
>>>>> Changes since v4:
>>>>>
>>>>> - Updated comment at the start of drm_dp_cec.c
>>>>> - Add edid pointer to drm_dp_cec_configure_adapter
>>>>> - Reworked the last patch (adding CEC to i915) based on Ville's comments
>>>>> and my MST testing:
>>>>> - register/unregister CEC in intel_dp_connector_register/unregister
>>>>> - add comment and check if connector is registered in long_pulse
>>>>> - unregister CEC if an MST 'connector' is detected.
>>>>>
>>>>> _______________________________________________
>>>>> dri-devel mailing list
>>>>> dri-devel@lists.freedesktop.org
>>>>> https://lists.freedesktop.org/mailman/listinfo/dri-devel
>>>>>
>>>>
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>>
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