On 08/12/2017 11:01 AM, Hans Verkuil wrote: > From: Hans Verkuil <hans.verkuil@xxxxxxxxx> > > This patch series adds support for the DisplayPort CEC-Tunneling-over-AUX > feature. This patch series is based on 4.13-rc4 which has all the needed cec > and drm 4.13 patches merged. > > This patch series has been tested with my NUC7i5BNK and a Samsung USB-C to > HDMI adapter. > > 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), 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. > ---------------------------------------------------------------------- > > 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). > > Note that a colleague who actually knows his way around a soldering iron > modified an UpTab DisplayPort-to-HDMI adapter for me, hooking up the CEC > pin. And after that change it worked. I also received confirmation that > this really is a chicken-and-egg situation: it is because there is no CEC > support for this feature in any OS that they do not hook up the CEC pin. > > So 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. > > Changes since v1: > > - Incorporated Sean's review comments in patch 1/3. Ping? Who is supposed to merge this? Is there anything I should do? I'd love to get this in for 4.14... Regards, Hans _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
