Feature Request: Add Chrontel CH7218 to the VRR PCON whitelist (patch provided)

[jwittlincohen]

Describe the bug

Describe the problem
VRR doesn't work with Ugreen DP -> HDMI 2.1 adapter (model 85564, DP134) or the similar cable utilizing the same chipset, without whitelisting the CH7218 chipset in the VRR PCON list.

This is significant as this is the only chipset/product on the market that offers:

1. 4K 144 Hz (or greater - 144 Hz confirmed on a LG C4, which is its max refresh rate) 10-bit 4:4:4 output - the VMM7100 chipset-based adapters and cables are limited to 4K 120 Hz

2. Functioning and stable Freesync VRR out-of-the-box without needing to flash a custom firmware.

3. Support confirmed for HDMI-VRR. Other products only support TVs with Freesync, meaning this adapter can not only provide HDMI 2.1 bandwidth but also VRR functionality for TVs that lack Freesync support. This has been confirmed by several users.

4. HDMI-CEC that has been tested and works out of the box in Steam OS 3.9, and presumably could work in Bazzite as well.

What did you expect to happen?

Working VRR with this dongle and cable, more broadly, with the chip inside which is Chrontel CH7218

Describe the target user/application
Users that want 4K 120Hz+ without chroma subsampling, and also users that want HDMI-VRR support on TVs that do not have Freesync. Currently, HDMI is limited to HDMI 2.0 bandwidth, which requires 4:2:0 chroma at 4K 120 Hz, and only supports Freesync, not HDMI-VRR, a HDMI 2.1 feature.

How do you plan to validate this feature

Tomasz Pakuła already confirmed by adding the chip's ID to the VRR whitelist. He tested VRR functionality with RX an 9070 XT and found it works perfectly, even better than the already supported VMM7100 from synaptics. VRR is more stable, HDR switching is more reliable AND this chip supports HDMI CEC tunneling.

Tomasz also provided a whitelist patch: https://gitlab.freedesktop.org/-/project/4522/uploads/623baa4303bcaf14413767aba7b699d6/0001-amdgpu-Add-CH7218-PCON-to-the-VRR-whitelist.patch

For additional context, see https://gitlab.freedesktop.org/drm/amd/-/issues/4773

Session Logs

Not relevant

Hardware

UGreen 8K DP to HDMI Adapter: https://www.amazon.com/dp/B0FQCF62CD

UGreen 8K DP to HDMI Cable: https://www.amazon.com/dp/B0CJ4YGDJH?ref=ppx_yo2ov_dt_b_fed_asin_title&th=1

Extra information or context

No response

[xXJSONDeruloXx]

https://github.com/bazzite-org/kernel-bazzite/issues/39

More of a kernel patch I suppose, related issue here

[SimpleHeuristics]

Not really relevant to the AMD side of things but just to add a datapoint from Nvidia side.

So I bought this adapter to try with my Nvidia pc as well to see if I could get CEC tunneling.

The adapter works on desktop however even though there is a VRR toggle this does not actually trigger VRR on the TV (LG C1) so similar to what is happening on the amd side.

Not sure if this something that needs to be fixed by Nvidia or if it can also be patched in the kernel.

Also no CEC device appears when listing devices under /dev/ at least on Nvidia, not sure if this works out of the box with AMD.

[xXJSONDeruloXx]

regarding the CEC tunneling, I think the current implementation in bazzite with libcec is userspace level, not kernel level. I am drafting a rework here

#3652

per the https://github.com/Lawstorant/cec-toolbox/tree/main repo as referenced in the ugreen adaptor testing reddit thread here:

https://www.reddit.com/r/linux_gaming/comments/1pkdfcm/ugreen_knight_the_holy_grail_of_hdmi_21_dongles/

my understanding is this move to basing off v41-utils rather than libcec should facilitate sending on cec bridge from DP port 1.3+, not just from USB > adaptor > bridged hdmi cable.

I have the pulse 8 adaptor, as well as the ugreen one coming in today, will test new version against both to make sure we dont break pulse8 in the process.

[12eward]

bazzite-org/kernel-bazzite#39

More of a kernel patch I suppose, related issue here

The Bazzite kernel repo linked here is now archived, did Bazzite move to another kernel repo?