platform/x86: apple-gmux: Add acpi_video_get_backlight_type() check

Make apple-gmux backlight registration honor the acpi_backlight=...
kernel commandline option which is used to select the backlight
control method on x86/ACPI devices.
Reported-and-tested-by: Aditya Garg <gargaditya08@live.com>
Link: https://lore.kernel.org/platform-driver-x86/BM1PR01MB0931B467250831916F7C55B3B8A59@BM1PR01MB0931.INDPRD01.PROD.OUTLOOK.COM/Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/r/20230307113813.359743-1-hdegoede@redhat.com

drivers/platform/x86/apple-gmux.c

@@ -23,6 +23,7 @@
 #include <linux/pci.h>
 #include <linux/vga_switcheroo.h>
 #include <linux/debugfs.h>
+#include <acpi/video.h>
 #include <asm/io.h>
 
 /**
@@ -781,8 +782,9 @@ static int gmux_probe(struct pnp_dev *pnp, const struct pnp_device_id *id)
 	struct apple_gmux_data *gmux_data;
 	struct resource *res;
 	struct backlight_properties props;
-	struct backlight_device *bdev;
+	struct backlight_device *bdev = NULL;
 	u8 ver_major, ver_minor, ver_release;
+	bool register_bdev = true;
 	int ret = -ENXIO;
 	acpi_status status;
 	unsigned long long gpe;
@@ -859,6 +861,10 @@ static int gmux_probe(struct pnp_dev *pnp, const struct pnp_device_id *id)
 	props.type = BACKLIGHT_PLATFORM;
 	props.max_brightness = gmux_read32(gmux_data, GMUX_PORT_MAX_BRIGHTNESS);
 
+#if IS_REACHABLE(CONFIG_ACPI_VIDEO)
+	register_bdev = acpi_video_get_backlight_type() == acpi_backlight_apple_gmux;
+#endif
+	if (register_bdev) {
 		/*
 		 * Currently it's assumed that the maximum brightness is less than
 		 * 2^24 for compatibility with old gmux versions. Cap the max
@@ -886,6 +892,7 @@ static int gmux_probe(struct pnp_dev *pnp, const struct pnp_device_id *id)
 		 * Disable the other backlight choices.
 		 */
 		apple_bl_unregister();
+	}
 
 	gmux_data->power_state = VGA_SWITCHEROO_ON;