#define GMUX_BRIGHTNESS_MASK 0x00ffffff
#define GMUX_MAX_BRIGHTNESS GMUX_BRIGHTNESS_MASK
+# define MMIO_GMUX_MAX_BRIGHTNESS 0xffff
+
static u8 gmux_pio_read8(struct apple_gmux_data *gmux_data, int port)
{
return inb(gmux_data->iostart + port);
memset(&props, 0, sizeof(props));
props.type = BACKLIGHT_PLATFORM;
- props.max_brightness = gmux_read32(gmux_data, GMUX_PORT_MAX_BRIGHTNESS);
+
+ /*
+ * All MMIO gmux's have 0xffff as max brightness, but some iMacs incorrectly
+ * report 0x03ff, despite the firmware being happy to set 0xffff as the brightness
+ * at boot. Force 0xffff for all MMIO gmux's so they all have the correct brightness
+ * range.
+ */
+ if (type == APPLE_GMUX_TYPE_MMIO)
+ props.max_brightness = MMIO_GMUX_MAX_BRIGHTNESS;
+ else
+ 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;