FAILED: patch "[PATCH] drm/amd/display: Initialise backlight level values from hw" failed to apply to 6.12-stable tree

The patch below does not apply to the 6.12-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.12.y
git checkout FETCH_HEAD
git cherry-pick -x 52d3d115e9cc975b90b1fc49abf6d36ad5e8847a
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026012010-maybe-province-85bf@gregkh' --subject-prefix 'PATCH 6.12.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 52d3d115e9cc975b90b1fc49abf6d36ad5e8847a Mon Sep 17 00:00:00 2001
From: Vivek Das Mohapatra <[email protected]>
Date: Mon, 12 Jan 2026 15:28:56 +0000
Subject: [PATCH] drm/amd/display: Initialise backlight level values from hw

Internal backlight levels are initialised from ACPI but the values are sometimes out of sync with the levels in effect until there has been a read from hardware (eg triggered by reading from sysfs).

This means that the first drm_commit can cause the levels to be set to a different value than the actual starting one, which results in a sudden change in brightness.

This path shows the problem (when the values are out of sync):

amdgpu_dm_atomic_commit_tail()
-> amdgpu_dm_commit_streams()
-> amdgpu_dm_backlight_set_level(..., dm->brightness[n])

This patch calls the backlight ops get_brightness explicitly at the end of backlight registration to make sure dm->brightness[n] is in sync with the actual hardware levels.

index 936c3bc3f2d6..fae88ce8327f 100644
@@ -5266,6 +5266,8 @@ amdgpu_dm_register_backlight_device(struct amdgpu_dm_connector *aconnector)
 	struct amdgpu_dm_backlight_caps *caps;
 	char bl_name[16];
 	int min, max;
+	int real_brightness;
+	int init_brightness;
 
 	if (aconnector->bl_idx == -1)
 		return;

@@ -5290,6 +5292,8 @@ amdgpu_dm_register_backlight_device(struct amdgpu_dm_connector *aconnector)
 	} else
 		props.brightness = props.max_brightness = MAX_BACKLIGHT_LEVEL;
 
+	init_brightness = props.brightness;
+
 	if (caps->data_points && !(amdgpu_dc_debug_mask & DC_DISABLE_CUSTOM_BRIGHTNESS_CURVE)) {
 		drm_info(drm, "Using custom brightness curve\n");
 		props.scale = BACKLIGHT_SCALE_NON_LINEAR;

@@ -5308,8 +5312,20 @@ amdgpu_dm_register_backlight_device(struct amdgpu_dm_connector *aconnector)
 	if (IS_ERR(dm->backlight_dev[aconnector->bl_idx])) {
 		drm_err(drm, "DM: Backlight registration failed!\n");
 		dm->backlight_dev[aconnector->bl_idx] = NULL;
-	} else
+	} else {
+		/*
+		 * dm->brightness[x] can be inconsistent just after startup until
+		 * ops.get_brightness is called.
+		 */
+		real_brightness =
+			amdgpu_dm_backlight_ops.get_brightness(dm->backlight_dev[aconnector->bl_idx]);
+
+		if (real_brightness != init_brightness) {
+			dm->actual_brightness[aconnector->bl_idx] = real_brightness;
+			dm->brightness[aconnector->bl_idx] = real_brightness;
+		}
 		drm_dbg_driver(drm, "DM: Registered Backlight device: %s\n", bl_name);
+	}
 }
 
 static int initialize_plane(struct amdgpu_display_manager *dm,