Bug 213715

Summary: failed to change brightness of HDR panel on AMD GREEN_SARDINE through aux
Product: Drivers Reporter: Pengyu Ma (mapengyu)
Component: Video(DRI - non Intel)Assignee: drivers_video-dri
Status: NEW ---    
Severity: blocking CC: alexdeucher, mario.limonciello
Priority: P1    
Hardware: All   
OS: Linux   
Kernel Version: 5.14.0-rc1+ Tree: Mainline
Regression: No
Attachments: dmesg
4k display edid

Description Pengyu Ma 2021-07-13 16:27:24 UTC
Created attachment 297819 [details]
dmesg

HW: ThinkPad P14s gen 2a
CPU: AMD Ryzen 7 PRO 5850U with Radeon Graphics
Panel: BOE 2434 and  CSO 5127

brightness can't be controlled through AUX.
It works with parameter "amdgpu.backlight=0"

dmesg attached.
Comment 1 Pengyu Ma 2021-07-13 16:29:49 UTC
Created attachment 297821 [details]
4k display edid
Comment 2 Mario Limonciello (AMD) 2021-07-20 16:08:38 UTC
I would suggest to work with BOE and CSO to fix the DPCD values in panel firmware to not report aux control if it is not functional.

You can see the kernel checks the DPCD to determine whether to use AUX or PWM.

https://github.com/torvalds/linux/blob/c010efb7f0bc0c3cb2cd26b000f71d4bd0c427cd/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c#L2433

BTW this behavior has been also been reported in the past, so a heuristic may be introduced at some point in the future for the buggy panel firmware: https://gitlab.freedesktop.org/drm/amd/-/issues/1438