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 (hverkuil@xxxxxxxxx) 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@xxxxxxxxxxxxxxxxxxxxx > https://lists.freedesktop.org/mailman/listinfo/dri-devel > _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
