On Mon, Aug 10, 2026 at 11:02:32PM +1000, Jonathan Gray wrote:
> On Mon, Aug 10, 2026 at 07:12:24AM +0100, Jason McIntyre wrote:
> > > try this revert of 6.18.42's
> > > drm/amd/display: Fix backlight max_brightness to match exported range
> > >
> >
> > yes, the revert fixes it.
> >
> > thanks,
> > jmc
>
> appears to be the same problem described in
> https://gitlab.freedesktop.org/drm/amd/-/work_items/5562
>
> Can you drop the previous patch and try the one below?
>
> adapted from
> drm/amd/display: Set default backlight without ACPI support
> https://lore.kernel.org/amd-gfx/[email protected]/
>
this diff does not fix the issue, i'm afraid.
jmc
> Index: sys/dev/pci/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> ===================================================================
> RCS file: /cvs/src/sys/dev/pci/drm/amd/display/amdgpu_dm/amdgpu_dm.c,v
> diff -u -p -r1.204 amdgpu_dm.c
> --- sys/dev/pci/drm/amd/display/amdgpu_dm/amdgpu_dm.c 10 Aug 2026 06:28:36
> -0000 1.204
> +++ sys/dev/pci/drm/amd/display/amdgpu_dm/amdgpu_dm.c 10 Aug 2026 12:49:15
> -0000
> @@ -4933,20 +4933,16 @@ static void amdgpu_dm_update_backlight_c
> caps->caps_valid = false;
> }
> }
> -
> +#else
> + if (caps->aux_support)
> + return;
> +#endif
> if (!caps->caps_valid) {
> caps->min_input_signal = AMDGPU_DM_DEFAULT_MIN_BACKLIGHT;
> caps->max_input_signal = AMDGPU_DM_DEFAULT_MAX_BACKLIGHT;
> + caps->ac_level = caps->dc_level = 50;
> caps->caps_valid = true;
> }
> -#else
> - if (caps->aux_support)
> - return;
> -
> - caps->min_input_signal = AMDGPU_DM_DEFAULT_MIN_BACKLIGHT;
> - caps->max_input_signal = AMDGPU_DM_DEFAULT_MAX_BACKLIGHT;
> - caps->caps_valid = true;
> -#endif
> }
>
> static int get_brightness_range(const struct amdgpu_dm_backlight_caps *caps,
>
