[RFC 1/2] ACPI: video: Simplify __acpi_video_get_backlight_type()

Hans de Goede
2022-11-05T14:54:08Z

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@redhat.com>
---
drivers/acpi/video_detect.c | 36 +++++++++++++++++-------------------
1 file changed, 17 insertions(+), 19 deletions(-)

diff --git a/drivers/acpi/video_detect.c b/drivers/acpi/video_detect.c
index b2a616287638..ec7421a3986f 100644
--- a/drivers/acpi/video_detect.c
+++ b/drivers/acpi/video_detect.c
@@ -687,6 +687,16 @@ 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.
@@ -732,26 +742,14 @@ static enum acpi_backlight_type __acpi_video_get_backlight_type(bool native)
if (apple_gmux_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;
--
2.37.3