On 08/12/2017 11:01 AM, Hans Verkuil wrote:
> From: Hans Verkuil <hans.verk...@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 (hverk...@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...
Regards,
Hans
