The apple-gmux driver only binds to old GMUX devices which have an IORESOURCE_IO resource (using inb()/outb()) rather then memory-mapped IO (IORESOURCE_MEM). T2 MacBooks use the new style GMUX devices (with IORESOURCE_MEM access), so these are not supported by the apple-gmux driver. This is not a problem since they have working ACPI video backlight support. But the apple_gmux_present() helper only checks if an ACPI device with the "APP000B" HID is present, causing acpi_video_get_backlight_type() to return acpi_backlight_apple_gmux disabling the acpi_video backlight device. Add a new apple_gmux_backlight_present() helper which checks that the "APP000B" device actually is an old GMUX device with an IORESOURCE_IO resource. This fixes the acpi_video0 backlight no longer registering on T2 MacBooks. Note people are working to add support for the new style GMUX to Linux: https://github.com/kekrby/linux-t2/commits/wip/hybrid-graphics Once this lands this patch should be reverted so that acpi_video_get_backlight_type() also prefers the gmux on new style GMUX MacBooks, but for now this is necessary to avoid regressing backlight control on T2 Macs. Fixes: 21245df307cb ("ACPI: video: Add Apple GMUX brightness control detection") Reported-and-tested-by: Aditya Garg <gargaditya08@xxxxxxxx> Signed-off-by: Hans de Goede <hdegoede@xxxxxxxxxx> --- drivers/acpi/video_detect.c | 23 ++++++++++++++++++++++- 1 file changed, 22 insertions(+), 1 deletion(-) diff --git a/drivers/acpi/video_detect.c b/drivers/acpi/video_detect.c index a934bbc9dd37..1b78c7434492 100644 --- a/drivers/acpi/video_detect.c +++ b/drivers/acpi/video_detect.c @@ -34,6 +34,7 @@ #include <linux/module.h> #include <linux/pci.h> #include <linux/platform_data/x86/nvidia-wmi-ec-backlight.h> +#include <linux/pnp.h> #include <linux/types.h> #include <linux/workqueue.h> #include <acpi/video.h> @@ -105,6 +106,26 @@ static bool nvidia_wmi_ec_supported(void) } #endif +static bool apple_gmux_backlight_present(void) +{ + struct acpi_device *adev; + struct device *dev; + + adev = acpi_dev_get_first_match_dev(GMUX_ACPI_HID, NULL, -1); + if (!adev) + return false; + + dev = acpi_get_first_physical_node(adev); + if (!dev) + return false; + + /* + * drivers/platform/x86/apple-gmux.c only supports old style + * Apple GMUX with an IO-resource. + */ + return pnp_get_resource(to_pnp_dev(dev), IORESOURCE_IO, 0) != NULL; +} + /* Force to use vendor driver when the ACPI device is known to be * buggy */ static int video_detect_force_vendor(const struct dmi_system_id *d) @@ -767,7 +788,7 @@ static enum acpi_backlight_type __acpi_video_get_backlight_type(bool native) if (nvidia_wmi_ec_present) return acpi_backlight_nvidia_wmi_ec; - if (apple_gmux_present()) + if (apple_gmux_backlight_present()) return acpi_backlight_apple_gmux; /* Use ACPI video if available, except when native should be preferred. */ -- 2.38.1
