[Bug 213715] New: failed to change brightness of HDR panel on AMD GREEN_SARDINE through aux

[Bug 213715] New: failed to change brightness of HDR panel on AMD GREEN_SARDINE through aux

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=213715

            Bug ID: 213715
           Summary: failed to change brightness of HDR panel on AMD
                    GREEN_SARDINE through aux
           Product: Drivers
           Version: 2.5
    Kernel Version: 5.14.0-rc1+
          Hardware: All
                OS: Linux
              Tree: Mainline
            Status: NEW
          Severity: blocking
          Priority: P1
         Component: Video(DRI - non Intel)
          Assignee: drivers_video-dri@kernel-bugs.osdl.org
          Reporter: mapengyu@gmail.com
        Regression: No

Created attachment 297819
  --> https://bugzilla.kernel.org/attachment.cgi?id=297819&action=edit
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.

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[Bug 213715] failed to change brightness of HDR panel on AMD GREEN_SARDINE through aux

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=213715

--- Comment #1 from Pengyu Ma (mapengyu@gmail.com) ---
Created attachment 297821
  --> https://bugzilla.kernel.org/attachment.cgi?id=297821&action=edit
4k display edid

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[Bug 213715] failed to change brightness of HDR panel on AMD GREEN_SARDINE through aux

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=213715

mario.limonciello@amd.com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |mario.limonciello@amd.com

--- Comment #2 from mario.limonciello@amd.com ---
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

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