From: Hans Verkuil hans.verkuil@cisco.com
Now that the DisplayPort CEC-Tunneling-over-AUX drm+i915 support has been merged in the mainline kernel it is time to roll this out to nouveau and amdgpu as well.
I combined both in the same patch series since both depend on the same first patch, the comments in this cover letter apply to both and the implementation is also very similar (and simple).
As mentioned, the first patch is required for this: it adds checks that the drm_dp_cec functions are called with a working aux implementation. These checks weren't necessary for the i915, but nouveau and amdgpu require them.
The next two patches update a comment in drm_dp_cec.c and fix a bug in sideband AUX handling that I found while researching CEC Tunneling over an MST hub. It's there to prevent others from stumbling over the same bug in the future.
The fourth patch adds support for CEC to the nouveau driver.
The last patch adds support for CEC to the amdgpu driver. However, there appear to be two classes of amdgpu hardware: as a discrete GPU or integrated. I only have a discrete GPU, so I can't test the integrated GPU support and I only implemented this for the discrete GPU case.
If someone has the integrated GPU and wants to get this working and is willing to do some testing, then please contact me. It shouldn't be difficult. You will likely have to buy a working DP-to-HDMI adapter. See https://hverkuil.home.xs4all.nl/cec-status.txt for a (sadly very short) list of working adapters.
Note that I may be completely off-base regarding what atombios_dp.c does, it's the first time I ever looked at amdgpu code.
Two notes on CEC-Tunneling-over-AUX:
1) You need to be very careful about which USB-C/DP/mini-DP to HDMI adapters you buy. Only a few support this feature correctly today. Known chipsets that support this are Parade PS175 & PS176 and MegaChips 2900. Unfortunately almost all Parade-based adapters do not hook up the HDMI CEC pin to the chip, making them useless for this. The Parade reference design was only recently changed to hook up this pin, so perhaps this situation will change for new Parade-based adapters.
Adapters based on the new MegaChips 2900 fare much better: it appears that their reference design *does* hook up the CEC pin. Club3D has adapters using this device for USB-C, DP and mini-DP to HDMI, and they all work fine.
If anyone finds other adapters that work besides those I list in https://hverkuil.home.xs4all.nl/cec-status.txt, please let me know and I'll add them to the list.
Linux is the first OS that supports this feature, so I am not surprised that HW support for this has been poor. Hopefully this will change going forward. BTW, note the irony that CEC is now supported for DP-to-HDMI adapters, but not for the native HDMI ports on NVIDIA/AMD/Intel GPUs.
2) CEC-Tunneling does not work (yet?) if there is an MST hub in between. I'm still researching this but this might be a limitation of MST.
Regards,
Hans
Hans Verkuil (5): drm_dp_cec: check that aux has a transfer function drm_dp_cec: add note about good MegaChips 2900 CEC support drm_dp_mst_topology: fix broken drm_dp_sideband_parse_remote_dpcd_read() drm/nouveau: add DisplayPort CEC-Tunneling-over-AUX support drm/amdgpu: add DisplayPort CEC-Tunneling-over-AUX support
.../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 13 +++++++++++-- .../display/amdgpu_dm/amdgpu_dm_mst_types.c | 2 ++ drivers/gpu/drm/drm_dp_cec.c | 18 +++++++++++++++++- drivers/gpu/drm/drm_dp_mst_topology.c | 1 + drivers/gpu/drm/nouveau/nouveau_connector.c | 17 +++++++++++++++-- 5 files changed, 46 insertions(+), 5 deletions(-)