Enable Adaptive Sync over PCON when HDMI VRR detected - (Upstream amd drm)

[DeNo64]

Your system information

• Steam client version: 1766529085
• SteamOS version: 3.7.19
• Opted into Steam client beta?: No
• Opted into SteamOS beta?: No
• Have you checked for updates in Settings > System?: Yes

Please describe your issue in as much detail as possible:

VRR (Adaptive Sync) & ALLM don't natively work on displays which do not support Freesync (only support HDMI 2.1 VRR). The workaround is to patch the EDID to enable Freesync based on HDMI (forum) VRR info on the EDID.
But doing this on SteamOS can be complicated due to its read-only nature.

There is an amd drm issue with patches to apply this workaround within the EDID parsing when using PCON (DisplayPort -> HDMI 2.1).

It would be great to see this patch in a Preview or even a Main release to test this on Steam Deck. Especially with Steam Machine around the corner not supporting HDMI 2.1 (VRR & ALLM), using Display Port in this way would be crucial for us with TV which don't support Freesync to still use VRR & ALLM.

Steps for reproducing this issue:

1. Plug Steam Deck into JSAUX 7-in-1 dock (HB0705) connected to LG C9, which only supports HDMI 2.1 VRR and G-SYNC Compatible

2. VRR not available

3. Plug Steam Deck into JSAUX 7-in-1 dock (HB0705) connected to AW3425DW, which supports HDMI 2.1 VRR, G-SYNC Compatible, and Freesync Premium Pro

4. VRR available