Re: wsdisplay brightness issue on amd64

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]/

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,