[PATCHv2 0/3] drm/i915: add DisplayPort CEC-Tunneling-over-AUX support

[Daniel Vetter]

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 at cisco.com>
> > 
> > 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 at xs4all.nl) 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