platform/x86: nvidia-wmi-ec-backlight: Use acpi_video_get_backlight_type()

Add an acpi_video_get_backlight_type() == acpi_backlight_nvidia_wmi_ec
check. This will make nvidia-wmi-ec-backlight properly honor the user
selecting a different backlight driver through the acpi_backlight=...
kernel commandline option.

Since the auto-detect code check for nvidia-wmi-ec-backlight in
drivers/acpi/video_detect.c already checks that the WMI advertised
brightness-source is the embedded controller, this new check makes it
unnecessary for nvidia_wmi_ec_backlight_probe() to check this itself.
Suggested-by: Daniel Dadap <ddadap@nvidia.com>
Reviewed-by: Daniel Dadap <ddadap@nvidia.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>

drivers/platform/x86/Kconfig

@@ -93,6 +93,7 @@ config PEAQ_WMI
 
 config NVIDIA_WMI_EC_BACKLIGHT
 	tristate "EC Backlight Driver for Hybrid Graphics Notebook Systems"
+	depends on ACPI_VIDEO
 	depends on ACPI_WMI
 	depends on BACKLIGHT_CLASS_DEVICE
 	help

drivers/platform/x86/nvidia-wmi-ec-backlight.c

@@ -10,6 +10,7 @@
 #include <linux/platform_data/x86/nvidia-wmi-ec-backlight.h>
 #include <linux/types.h>
 #include <linux/wmi.h>
+#include <acpi/video.h>
 
 /**
  * wmi_brightness_notify() - helper function for calling WMI-wrapped ACPI method
@@ -87,19 +88,10 @@ static int nvidia_wmi_ec_backlight_probe(struct wmi_device *wdev, const void *ct
 {
 	struct backlight_properties props = {};
 	struct backlight_device *bdev;
-	u32 source;
 	int ret;
 
-	ret = wmi_brightness_notify(wdev, WMI_BRIGHTNESS_METHOD_SOURCE,
-	                           WMI_BRIGHTNESS_MODE_GET, &source);
-	if (ret)
-		return ret;
-
-	/*
-	 * This driver is only to be used when brightness control is handled
-	 * by the EC; otherwise, the GPU driver(s) should control brightness.
-	 */
-	if (source != WMI_BRIGHTNESS_SOURCE_EC)
+	/* drivers/acpi/video_detect.c also checks that SOURCE == EC */
+	if (acpi_video_get_backlight_type() != acpi_backlight_nvidia_wmi_ec)
 		return -ENODEV;
 
 	/*