diff mbox series

[3/6,SRU,OEM-6.0] ACPI: video: Refactor acpi_video_get_backlight_type() a bit

Message ID 20230427074116.188543-4-acelan.kao@canonical.com
State New
Headers show
Series both dell_backlight and nvidia_0 backlight interface appear, and can't adjust the display brightness | expand

Commit Message

AceLan Kao April 27, 2023, 7:41 a.m. UTC 
From: Hans de Goede <hdegoede@redhat.com>

BugLink: https://launchpad.net/bugs/2017774

Refactor acpi_video_get_backlight_type() so that the heuristics /
detection steps are stricly in order of descending precedence.

Also move the comments describing the steps to when the various steps are
actually done, to avoid the comments getting out of sync with the code.

Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
(cherry picked from commit b39be9f441f9d7320e6020bdf8ec1522d6c81d1e)
Signed-off-by: Chia-Lin Kao (AceLan) <acelan.kao@canonical.com>
---
 drivers/acpi/video_detect.c | 39 ++++++++++++++++++++++---------------
 1 file changed, 23 insertions(+), 16 deletions(-)
diff mbox series

Patch

diff --git a/drivers/acpi/video_detect.c b/drivers/acpi/video_detect.c
index 37c42d671930..110ad1a3b7f0 100644
--- a/drivers/acpi/video_detect.c
+++ b/drivers/acpi/video_detect.c
@@ -625,16 +625,6 @@  static int acpi_video_backlight_notify(struct notifier_block *nb,
 /*
  * Determine which type of backlight interface to use on this system,
  * First check cmdline, then dmi quirks, then do autodetect.
- *
- * The autodetect order is:
- * 1) Is the acpi-video backlight interface supported ->
- *  no, use a vendor interface
- * 2) Is this a win8 "ready" BIOS and do we have a native interface ->
- *  yes, use a native interface
- * 3) Else use the acpi-video interface
- *
- * Arguably the native on win8 check should be done first, but that would
- * be a behavior change, which may causes issues.
  */
 static enum acpi_backlight_type __acpi_video_get_backlight_type(bool native)
 {
@@ -663,19 +653,36 @@  static enum acpi_backlight_type __acpi_video_get_backlight_type(bool native)
 		native_available = true;
 	mutex_unlock(&init_mutex);
 
+	/*
+	 * The below heuristics / detection steps are in order of descending
+	 * presedence. The commandline takes presedence over anything else.
+	 */
 	if (acpi_backlight_cmdline != acpi_backlight_undef)
 		return acpi_backlight_cmdline;
 
+	/* DMI quirks override any autodetection. */
 	if (acpi_backlight_dmi != acpi_backlight_undef)
 		return acpi_backlight_dmi;
 
-	if (!(video_caps & ACPI_VIDEO_BACKLIGHT))
-		return acpi_backlight_vendor;
-
-	if (acpi_osi_is_win8() && native_available)
-		return acpi_backlight_native;
+	/* 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;
+	}
 
-	return acpi_backlight_video;
+	/* No ACPI video (old hw), use vendor specific fw methods. */
+	return acpi_backlight_vendor;
 }
 
 enum acpi_backlight_type acpi_video_get_backlight_type(void)