AMDGPU & Nouveau Getting HDMI CEC Support For DisplayPort/USB-C To HDMI Adapters

[phoronix]

Phoronix: AMDGPU & Nouveau Getting HDMI CEC Support For DisplayPort/USB-C To HDMI Adapters

Another drm-misc-next pull request was sent in Wednesday with new feature material slated for the Linux 4.20~5.0 kernel release by way of DRM-Next...

http://www.phoronix.com/scan.php?page=news_item&px=AMDGPU-Nouveau-CEC-Tunnel

[Marc1n]

Now they need to fix HDMI 2.0 and UHD@60Hz support for boards that advertise only HDMI 1.4 support.
It's silly when you have Ryzen APU that clearly supports HDMI 2.0 and can't go above UHD@30Hz because board manufacturer wanted to save little money on HDMI 2.0 certification.
Windows driver is simply ignoring ACPI tables and using HDMI 2.0 if hardware supports it while Linux Kernel is blindly following what ACPI tables tell it.
And as Windows is the de facto the standard i'm not expecting for situation to change anytime soon.

[xcom]

CEC only works if I buy a DisplayPort >> HDMI converter ?

[M@yeulC]

So, am I reading this right, and CEC is actually supported on AMDGPU/Nouveau? Can I just kook up some HDMI device and it will work? That's awesome!

[starshipeleven]

CEC only works if I buy a DisplayPort >> HDMI converter ?

Does your TV and other media boxes in the living room have Displayport?

Afaik CEC isn't part of the spec of Displayport, so this makes sense only if the system detects that you are using an HDMI adapter.

[starshipeleven]

So, am I reading this right, and CEC is actually supported on AMDGPU/Nouveau? Can I just kook up some HDMI device and it will work? That's awesome!

No, this just means that the cards that have CEC support on HDMI will be able to use it also on Displayports with HDMI adapters.

I'm somewhat wondering if there are any GPUs apart from Intel iGPUs and embedded stuff that support CEC on Linux.

EDIT: seems like I'm wrong, see imirkin answer below.

[imirkin]

NVIDIA does not support CEC natively on desktop GPU HDMI ports, no amount of software will change that, the pins are just not hooked up for it. Not sure about AMD GPU's.

DP, however, provides a generic out-of-band i2c-ish protocol called DP AUX which enables passing various side-band data outside of the video/audio streams. Some DP -> HDMI active adapters (not the passive square peg/round hole ones, but the ones that actually do a protocol conversion) enable a DP source to send CEC data via DP AUX (in a standard way), which will then be sent over HDMI. This change enables sending CEC data to such adapters.

As Hans notes, however, far from all DP -> HDMI active adapters have this hooked up properly -- in fact most don't. So make sure you pick from his approved list unless you're feeling adventurous. See https://hverkuil.home.xs4all.nl/cec-status.txt for the list of adapters that have been tested.

[M@yeulC]

Thanks a lot for your answer, Ilia. This makes more sense indeed.

It's a shame CEC isn't wired up, though. I can't see this being too costly to do, when a dumb microcontroller is able to. AFAIK, AMD doesn't do it either.
I wish a similar standard existed for DP (together with more DP adoption).

[chithanh]

I think AMD does not support HDMI CEC natively either. It may have to do with the fact that CEC is patent encumbered and not wanting to pay royalties.

Some people say this is why the PS4 uses the APU's DP output with a Panasonic MN864xxx external HDMI encoder.