Patch "ACPI: video: Simplify __acpi_video_get_backlight_type()" has been added to the 6.1-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    ACPI: video: Simplify __acpi_video_get_backlight_type()

to the 6.1-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     acpi-video-simplify-__acpi_video_get_backlight_type.patch
and it can be found in the queue-6.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 07ee1aab2fbf52953b8030db9818e73b113537b8
Author: Hans de Goede <hdegoede@xxxxxxxxxx>
Date:   Mon Nov 14 15:44:58 2022 +0100

    ACPI: video: Simplify __acpi_video_get_backlight_type()
    
    [ Upstream commit a5df42521f328b45c9d89c13740e747be08ac66e ]
    
    Simplify __acpi_video_get_backlight_type() removing a nested if which
    makes the flow harder to follow.
    
    This also results in having only 1 exit point with
    return acpi_backlight_native instead of 2.
    
    Note this drops the (video_caps & ACPI_VIDEO_BACKLIGHT) check from
    the if (acpi_osi_is_win8() && native_available) return native path.
    Windows 8's hardware certification requirements include that there must
    be ACPI video bus backlight control, so the ACPI_VIDEO_BACKLIGHT check
    is redundant.
    
    Signed-off-by: Hans de Goede <hdegoede@xxxxxxxxxx>
    Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/acpi/video_detect.c b/drivers/acpi/video_detect.c
index 13f10fbcd7f0..0c17ee93f861 100644
--- a/drivers/acpi/video_detect.c
+++ b/drivers/acpi/video_detect.c
@@ -734,6 +734,16 @@ static bool google_cros_ec_present(void)
 	return acpi_dev_found("GOOG0004") || acpi_dev_found("GOOG000C");
 }
 
+/*
+ * Windows 8 and newer no longer use the ACPI video interface, so it often
+ * does not work. So on win8+ systems prefer native brightness control.
+ * Chromebooks should always prefer native backlight control.
+ */
+static bool prefer_native_over_acpi_video(void)
+{
+	return acpi_osi_is_win8() || google_cros_ec_present();
+}
+
 /*
  * Determine which type of backlight interface to use on this system,
  * First check cmdline, then dmi quirks, then do autodetect.
@@ -779,26 +789,14 @@ static enum acpi_backlight_type __acpi_video_get_backlight_type(bool native)
 	if (apple_gmux_backlight_present())
 		return acpi_backlight_apple_gmux;
 
-	/* Chromebooks should always prefer native backlight control. */
-	if (google_cros_ec_present() && native_available)
-		return acpi_backlight_native;
+	/* Use ACPI video if available, except when native should be preferred. */
+	if ((video_caps & ACPI_VIDEO_BACKLIGHT) &&
+	     !(native_available && prefer_native_over_acpi_video()))
+		return acpi_backlight_video;
 
-	/* On systems with ACPI video use either native or ACPI video. */
-	if (video_caps & ACPI_VIDEO_BACKLIGHT) {
-		/*
-		 * Windows 8 and newer no longer use the ACPI video interface,
-		 * so it often does not work. If the ACPI tables are written
-		 * for win8 and native brightness ctl is available, use that.
-		 *
-		 * The native check deliberately is inside the if acpi-video
-		 * block on older devices without acpi-video support native
-		 * is usually not the best choice.
-		 */
-		if (acpi_osi_is_win8() && native_available)
-			return acpi_backlight_native;
-		else
-			return acpi_backlight_video;
-	}
+	/* Use native if available */
+	if (native_available && prefer_native_over_acpi_video())
+		return acpi_backlight_native;
 
 	/* No ACPI video (old hw), use vendor specific fw methods. */
 	return acpi_backlight_vendor;