On Sat, Aug 19, 2017 at 02:05:16PM +0200, Hans Verkuil wrote: > 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... 1) you have commit rights, so only really need to find a reviewer. Not exactly sure who'd be a good reviewer, maybe Imre or Ville? 2) 4.14 is done, this will go into 4.15. Cheers, Daniel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
