Re: AMDGPU - Regression: Black screen due to commit 16dc8bc27c2aa3c93905d3e885e27f1e3535f09a

[Mario Limonciello]

On 6/21/25 11:07 AM, Walt Holman wrote:
> On Sat, Jun 21, 2025 at 11:03 AM Walt Holman <waltholman09@xxxxxxxxx> wrote:
> > On Sat, Jun 21, 2025 at 10:52 AM Mario Limonciello <superm1@xxxxxxxxxx> wrote:
> > > On 6/21/25 10:18 AM, Walt Holman wrote:
> > > > Hello,
> > > >
> > > > With the latest drm fixes this week on 6.16-rc2, I am experiencing a
> > > > black screen instead of the sddm greeter and the GPU appears to be
> > > > locked up. I can ssh into the laptop and reboot it, but that's about
> > > > it. I have bisected the commit to commit id:
> > > > 16dc8bc27c2aa3c93905d3e885e27f1e3535f09a and upon reverting the
> > > > commit, the system works as normal. The hardware is an Asus Rog
> > > > Zephyrus G16 with AMD Ryzen AI 9 HX 370 w/ Radeon 890M video. I'm able
> > > > to test patches etc.. if need be.
> > >
> > > Hi there,
> > >
> > > By chance do you have an OLED panel?  If so can you please try the patch
> > > attached to this bug?
> > >
> > > https://gitlab.freedesktop.org/drm/amd/-/issues/4338
> > >
> > > Thanks,
> > >
> > > > 16dc8bc27c2aa3c93905d3e885e27f1e3535f09a is the first bad commit
> > > > commit 16dc8bc27c2aa3c93905d3e885e27f1e3535f09a (HEAD)
> > > > Author: Mario Limonciello <mario.limonciello@xxxxxxx>
> > > > Date:   Thu May 29 09:46:32 2025 -0500
> > > >
> > > >       drm/amd/display: Export full brightness range to userspace
> > > >
> > > >       [WHY]
> > > >       Userspace currently is offered a range from 0-0xFF but the PWM is
> > > >       programmed from 0-0xFFFF.  This can be limiting to some software
> > > >       that wants to apply greater granularity.
> > > >
> > > >       [HOW]
> > > >       Convert internally to firmware values only when mapping custom
> > > >       brightness curves because these are in 0-0xFF range. Advertise full
> > > >       PWM range to userspace.
> > > >
> > > >       Cc: Mario Limonciello <mario.limonciello@xxxxxxx>
> > > >       Cc: Alex Deucher <alexander.deucher@xxxxxxx>
> > > >       Reviewed-by: Roman Li <roman.li@xxxxxxx>
> > > >       Signed-off-by: Mario Limonciello <mario.limonciello@xxxxxxx>
> > > >       Signed-off-by: Alex Hung <alex.hung@xxxxxxx>
> > > >       Tested-by: Daniel Wheeler <daniel.wheeler@xxxxxxx>
> > > >       Signed-off-by: Alex Deucher <alexander.deucher@xxxxxxx>
> > > >       (cherry picked from commit 8dbd72cb790058ce52279af38a43c2b302fdd3e5)
> > > >       Cc: stable@xxxxxxxxxxxxxxx
> > > >
> > > >    drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 41
> > > > +++++++++++++++++++++++++++--------------
> > > >    1 file changed, 27 insertions(+), 14 deletions(-)
> >
> > Yes, I do have an OLED panel and that patch does make it visible
> > again. It is still very dark, but visible.
> >
> > -Walt
>
> Upon rebooting again, the display was much brighter and is fine. Just
> the first boot after that was dark.
>
> -Walt

Thanks, this makes sense.  I suspect that because 0 means "off" for your 
panel that the patch you bisected to exposed running at 0 (or near 
enough to 0) that it caused this behavior.

That patch you tested will be upstreamed in a future promotion, and I 
think we can take it in a -fixes PR later in the 6.16 fixes cycle.

But there is one more thing I would like to confirm - on your system can 
you run with drm.debug=0x106 on the kernel command line and share me the 
output from this debug print?

https://github.com/torvalds/linux/blob/v6.16-rc2/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c#L4933