[PATCH 01/22] drm/i915/opregion: Improve backlight request condition

[Akihiko Odaki]

asle_set_backlight() needs to accept backlight request only if the
firmware controls the backlight. It used the following expression for
this purpose:
acpi_video_get_backlight_type() == acpi_backlight_native

This expression works well in practice, but has two semantic problems.
One is that it actually determines if a backlight device which directly
modifies hardware registers ("native backlight") exists. It is possible
that a device which does not have backlight at all incorrectly triggers
asle_set_backlight(), and the expression does not cover such a case.

Another problem is that acpi_video_get_backlight_type() always return
acpi_backlight_vendor in reality if CONFIG_ACPI_VIDEO is unset. It
means even its ability to determine the existence of native backlight is
somewhat limited.

This change introduces a new function backlight_device_non_raw_exists(),
which returns if the firmware is controlling the backlight, and is
always available if backlight support is enabled.

Signed-off-by: Akihiko Odaki <akihiko.odaki at daynix.com>
---
 drivers/gpu/drm/i915/display/intel_opregion.c |  3 ++-
 drivers/video/backlight/backlight.c           | 18 ++++++++++++++++++
 include/linux/backlight.h                     |  1 +
 3 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/display/intel_opregion.c b/drivers/gpu/drm/i915/display/intel_opregion.c
index caa07ef34f21..82ea02ab94c2 100644
--- a/drivers/gpu/drm/i915/display/intel_opregion.c
+++ b/drivers/gpu/drm/i915/display/intel_opregion.c
@@ -26,6 +26,7 @@
  */
 
 #include <linux/acpi.h>
+#include <linux/backlight.h>
 #include <linux/dmi.h>
 #include <linux/firmware.h>
 #include <acpi/video.h>
@@ -467,7 +468,7 @@ static u32 asle_set_backlight(struct drm_i915_private *dev_priv, u32 bclp)
 
 	drm_dbg(&dev_priv->drm, "bclp = 0x%08x\n", bclp);
 
-	if (acpi_video_get_backlight_type() == acpi_backlight_native) {
+	if (!backlight_device_non_raw_exists()) {
 		drm_dbg_kms(&dev_priv->drm,
 			    "opregion backlight request ignored\n");
 		return 0;
diff --git a/drivers/video/backlight/backlight.c b/drivers/video/backlight/backlight.c
index b788ff3d0f45..4f0ce463e250 100644
--- a/drivers/video/backlight/backlight.c
+++ b/drivers/video/backlight/backlight.c
@@ -516,6 +516,24 @@ struct backlight_device *backlight_device_get_by_name(const char *name)
 }
 EXPORT_SYMBOL(backlight_device_get_by_name);
 
+bool backlight_device_non_raw_exists(void)
+{
+	bool found = false;
+	struct backlight_device *bd;
+
+	mutex_lock(&backlight_dev_list_mutex);
+	list_for_each_entry(bd, &backlight_dev_list, entry) {
+		if (bd->props.type != BACKLIGHT_RAW) {
+			found = true;
+			break;
+		}
+	}
+	mutex_unlock(&backlight_dev_list_mutex);
+
+	return found;
+}
+EXPORT_SYMBOL(backlight_device_non_raw_exists);
+
 /* deprecated - use devm_backlight_device_unregister() */
 void backlight_device_unregister(struct backlight_device *bd)
 {
diff --git a/include/linux/backlight.h b/include/linux/backlight.h
index 614653e07e3a..364ef6f99a9e 100644
--- a/include/linux/backlight.h
+++ b/include/linux/backlight.h
@@ -444,6 +444,7 @@ int backlight_register_notifier(struct notifier_block *nb);
 int backlight_unregister_notifier(struct notifier_block *nb);
 struct backlight_device *backlight_device_get_by_name(const char *name);
 struct backlight_device *backlight_device_get_by_type(enum backlight_type type);
+bool backlight_device_non_raw_exists(void);
 int backlight_device_set_brightness(struct backlight_device *bd,
 				    unsigned long brightness);
 
-- 
2.37.3