[Intel-gfx] [PATCH v3] drm/i915/opregion: ignore firmware requests for backlight change

[Aaron Lu]

Some Thinkpad laptops' firmware will initiate a backlight level change
request through operation region on the events of AC plug/unplug, but
since we are not using firmware's interface to do the backlight setting
on these affected laptops, we do not want the firmware to use some
arbitrary value from its ASL variable to set the backlight level on
AC plug/unplug either.

Buglink: https://bugzilla.kernel.org/show_bug.cgi?id=76491
Buglink: https://bugzilla.kernel.org/show_bug.cgi?id=77091
Reported-and-tested-by: Igor Gnatenko <i.gnatenko.brain at gmail.com>
Reported-and-tested-by: Anton Gubarkov <anton.gubarkov at gmail.com>
Signed-off-by: Aaron Lu <aaron.lu at intel.com>
Acked-by: Jani Nikula <jani.nikula at intel.com>
---
v3:
  - use EXPORT_SYMBOL_GPL instead of EXPORT_SYMBOL;
  - add inline to stub
  as suggested by Rafael.

 drivers/acpi/video.c                  | 3 ++-
 drivers/gpu/drm/i915/intel_opregion.c | 9 +++++++++
 include/acpi/video.h                  | 2 ++
 3 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/drivers/acpi/video.c b/drivers/acpi/video.c
index fb9ffe9adc64..5bb1278e9324 100644
--- a/drivers/acpi/video.c
+++ b/drivers/acpi/video.c
@@ -241,13 +241,14 @@ static bool acpi_video_use_native_backlight(void)
 		return use_native_backlight_dmi;
 }
 
-static bool acpi_video_verify_backlight_support(void)
+bool acpi_video_verify_backlight_support(void)
 {
 	if (acpi_osi_is_win8() && acpi_video_use_native_backlight() &&
 	    backlight_device_registered(BACKLIGHT_RAW))
 		return false;
 	return acpi_video_backlight_support();
 }
+EXPORT_SYMBOL_GPL(acpi_video_verify_backlight_support);
 
 /* backlight device sysfs support */
 static int acpi_video_get_brightness(struct backlight_device *bd)
diff --git a/drivers/gpu/drm/i915/intel_opregion.c b/drivers/gpu/drm/i915/intel_opregion.c
index 2e2c71fcc9ed..4f6b53998d79 100644
--- a/drivers/gpu/drm/i915/intel_opregion.c
+++ b/drivers/gpu/drm/i915/intel_opregion.c
@@ -403,6 +403,15 @@ static u32 asle_set_backlight(struct drm_device *dev, u32 bclp)
 
 	DRM_DEBUG_DRIVER("bclp = 0x%08x\n", bclp);
 
+	/*
+	 * If the acpi_video interface is not supposed to be used, don't
+	 * bother processing backlight level change requests from firmware.
+	 */
+	if (!acpi_video_verify_backlight_support()) {
+		DRM_DEBUG_KMS("opregion backlight request ignored\n");
+		return 0;
+	}
+
 	if (!(bclp & ASLE_BCLP_VALID))
 		return ASLC_BACKLIGHT_FAILED;
 
diff --git a/include/acpi/video.h b/include/acpi/video.h
index ea4c7bbded4d..3d0bf9cd88c9 100644
--- a/include/acpi/video.h
+++ b/include/acpi/video.h
@@ -22,6 +22,7 @@ extern void acpi_video_unregister(void);
 extern void acpi_video_unregister_backlight(void);
 extern int acpi_video_get_edid(struct acpi_device *device, int type,
 			       int device_id, void **edid);
+extern bool acpi_video_verify_backlight_support(void);
 #else
 static inline int acpi_video_register(void) { return 0; }
 static inline void acpi_video_unregister(void) { return; }
@@ -31,6 +32,7 @@ static inline int acpi_video_get_edid(struct acpi_device *device, int type,
 {
 	return -ENODEV;
 }
+static inline bool acpi_video_verify_backlight_support() { return false; }
 #endif
 
 #endif
-- 
1.9.3