[PATCH 5/6][SRU][OEM-6.0] ACPI: video: Simplify __acpi_video_get_backlight_type()

[AceLan Kao]

From: Hans de Goede <hdegoede at redhat.com>

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

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 at redhat.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki at intel.com>
(backported from commit a5df42521f328b45c9d89c13740e747be08ac66e)
(AceLan: conflicts with non-existent if statments and removed non-existent
google_cros_ec_present())
Signed-off-by: Chia-Lin Kao (AceLan) <acelan.kao at canonical.com>
---
 drivers/acpi/video_detect.c | 34 ++++++++++++++++++----------------
 1 file changed, 18 insertions(+), 16 deletions(-)

diff --git a/drivers/acpi/video_detect.c b/drivers/acpi/video_detect.c
index addf6c061ecd..37aaf541bca1 100644
--- a/drivers/acpi/video_detect.c
+++ b/drivers/acpi/video_detect.c
@@ -622,6 +622,16 @@ static int acpi_video_backlight_notify(struct notifier_block *nb,
 	return NOTIFY_OK;
 }
 
+/*
+ * 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();
+}
+
 /*
  * Determine which type of backlight interface to use on this system,
  * First check cmdline, then dmi quirks, then do autodetect.
@@ -664,22 +674,14 @@ static enum acpi_backlight_type __acpi_video_get_backlight_type(bool native)
 	if (acpi_backlight_dmi != acpi_backlight_undef)
 		return acpi_backlight_dmi;
 
-	/* 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 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;
+
+	/* 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;
-- 
2.34.1