Re: wsdisplay brightness issue on amd64

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,
>