[REGRESSION] drm/amd/display: backlight brightness set to 0 at amdgpu initialization

[Lauri Tirkkonen]

On Fri, Jul 18 2025 20:14:08 -0500, Mario Limonciello wrote:
> OK, I think we need to do two things to figure out what's going on.
> 
> 1) Let's shift over to 6.16-rc6.  Once we've got a handle on the situation
> there we can iron out if there are other patches missing or this is also
> broken for you in 6.16.  If it's not working as expected there either we
> need it fixed there first anyway.

Same behavior on 6.16-rc6: brightness is set to 0 (max 399000),
minimally visible.

> 2) The starting brightness I don't expect to be "0".  We need to see what
> values were read out from the firmware. There is a debugging message we can
> catch if you boot with drm.debug=0x106.  Keep in mind you probably need to
> increase log_buf_len if your ring buffer is set too small too.
> 
> https://github.com/torvalds/linux/commit/4b61b8a390511a1864f26cc42bab72881e93468d
> 
> PS: I would rather you add logs into a gist, pastebin or a bug somewhere if
> you can.

[    3.210757] amdgpu 0000:03:00.0: [drm:amdgpu_dm_connector_late_register [amdgpu]] Backlight caps: min: 1000, max: 400000, ac 100, dc 32

full dmesg: https://termbin.com/o2q3

-- 
Lauri Tirkkonen | lotheac @ IRCnet