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. Regards, Hans Hans Verkuil (3): drm: add support for DisplayPort CEC-Tunneling-over-AUX drm-kms-helpers.rst: document the DP CEC helpers drm/i915: add DisplayPort CEC-Tunneling-over-AUX support Documentation/gpu/drm-kms-helpers.rst | 9 + drivers/gpu/drm/Kconfig | 10 ++ drivers/gpu/drm/Makefile | 1 + drivers/gpu/drm/drm_dp_cec.c | 302 ++++++++++++++++++++++++++++++++++ drivers/gpu/drm/i915/intel_dp.c | 18 +- include/drm/drm_dp_helper.h | 24 +++ 6 files changed, 360 insertions(+), 4 deletions(-) create mode 100644 drivers/gpu/drm/drm_dp_cec.c -- 2.13.2
