[PATCH v3 3/4] ACPI / video: Do not register backlight if win8 and native interface exists

[Aaron Lu]

According to Matthew Garrett, "Windows 8 leaves backlight control up
to individual graphics drivers rather than making ACPI calls itself.
There's plenty of evidence to suggest that the Intel driver for
Windows [8] doesn't use the ACPI interface, including the fact that
it's broken on a bunch of machines when the OS claims to support
Windows 8.  The simplest thing to do appears to be to disable the
ACPI backlight interface on these systems".

So for Win8 systems, if there is native backlight control interface
registered by GPU driver, ACPI video will not register its own. For
users who prefer to keep ACPI video's backlight interface, the existing
kernel cmdline option acpi_backlight=video can be used.

Signed-off-by: Aaron Lu <aaron.lu at intel.com>
Tested-by: Igor Gnatenko <i.gnatenko.brain at gmail.com>
Tested-by: Yves-Alexis Perez <corsac at debian.org>
---
 drivers/acpi/internal.h     |  5 ++---
 drivers/acpi/video.c        | 10 +++++-----
 drivers/acpi/video_detect.c | 14 ++++++++++++--
 3 files changed, 19 insertions(+), 10 deletions(-)

diff --git a/drivers/acpi/internal.h b/drivers/acpi/internal.h
index 20f4233..453ae8d 100644
--- a/drivers/acpi/internal.h
+++ b/drivers/acpi/internal.h
@@ -169,9 +169,8 @@ int acpi_create_platform_device(struct acpi_device *adev,
 					Video
   -------------------------------------------------------------------------- */
 #if defined(CONFIG_ACPI_VIDEO) || defined(CONFIG_ACPI_VIDEO_MODULE)
-bool acpi_video_backlight_quirks(void);
-#else
-static inline bool acpi_video_backlight_quirks(void) { return false; }
+bool acpi_osi_is_win8(void);
+bool acpi_video_verify_backlight_support(void);
 #endif
 
 #endif /* _ACPI_INTERNAL_H_ */
diff --git a/drivers/acpi/video.c b/drivers/acpi/video.c
index 3bd1eaa..343db59 100644
--- a/drivers/acpi/video.c
+++ b/drivers/acpi/video.c
@@ -1256,8 +1256,8 @@ acpi_video_switch_brightness(struct acpi_video_device *device, int event)
 	unsigned long long level_current, level_next;
 	int result = -EINVAL;
 
-	/* no warning message if acpi_backlight=vendor is used */
-	if (!acpi_video_backlight_support())
+	/* no warning message if acpi_backlight=vendor or a quirk is used */
+	if (!acpi_video_verify_backlight_support())
 		return 0;
 
 	if (!device->brightness)
@@ -1386,13 +1386,13 @@ acpi_video_bus_get_devices(struct acpi_video_bus *video,
 static int acpi_video_bus_start_devices(struct acpi_video_bus *video)
 {
 	return acpi_video_bus_DOS(video, 0,
-				  acpi_video_backlight_quirks() ? 1 : 0);
+				  acpi_osi_is_win8() ? 1 : 0);
 }
 
 static int acpi_video_bus_stop_devices(struct acpi_video_bus *video)
 {
 	return acpi_video_bus_DOS(video, 0,
-				  acpi_video_backlight_quirks() ? 0 : 1);
+				  acpi_osi_is_win8() ? 0 : 1);
 }
 
 static void acpi_video_bus_notify(struct acpi_device *device, u32 event)
@@ -1558,7 +1558,7 @@ acpi_video_bus_match(acpi_handle handle, u32 level, void *context,
 
 static void acpi_video_dev_register_backlight(struct acpi_video_device *device)
 {
-	if (acpi_video_backlight_support()) {
+	if (acpi_video_verify_backlight_support()) {
 		struct backlight_properties props;
 		struct pci_dev *pdev;
 		acpi_handle acpi_parent;
diff --git a/drivers/acpi/video_detect.c b/drivers/acpi/video_detect.c
index 940edbf..23d7d26 100644
--- a/drivers/acpi/video_detect.c
+++ b/drivers/acpi/video_detect.c
@@ -37,6 +37,7 @@
 #include <linux/acpi.h>
 #include <linux/dmi.h>
 #include <linux/pci.h>
+#include <linux/backlight.h>
 
 #include "internal.h"
 
@@ -233,11 +234,11 @@ static void acpi_video_caps_check(void)
 		acpi_video_get_capabilities(NULL);
 }
 
-bool acpi_video_backlight_quirks(void)
+bool acpi_osi_is_win8(void)
 {
 	return acpi_gbl_osi_data >= ACPI_OSI_WIN_8;
 }
-EXPORT_SYMBOL(acpi_video_backlight_quirks);
+EXPORT_SYMBOL(acpi_osi_is_win8);
 
 /* Promote the vendor interface instead of the generic video module.
  * This function allow DMI blacklists to be implemented by externals
@@ -283,6 +284,15 @@ int acpi_video_backlight_support(void)
 }
 EXPORT_SYMBOL(acpi_video_backlight_support);
 
+bool acpi_video_verify_backlight_support(void)
+{
+	if (!(acpi_video_support & ACPI_VIDEO_BACKLIGHT_FORCE_VIDEO) &&
+	    acpi_osi_is_win8() && backlight_device_registered(BACKLIGHT_RAW))
+		return false;
+	return acpi_video_backlight_support();
+}
+EXPORT_SYMBOL(acpi_video_verify_backlight_support);
+
 /*
  * Use acpi_backlight=vendor/video to force that backlight switching
  * is processed by vendor specific acpi drivers or video.ko driver.
-- 
1.8.4.12.g2ea3df6