ACPI: video: Fix Apple GMUX backlight detection

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@live.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
---
 drivers/acpi/video_detect.c | 23 ++++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

On Thu, Dec 15, 2022 at 10:41 AM Hans de Goede <hdegoede@redhat.com> wrote:
>
> 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@live.com>
> Signed-off-by: Hans de Goede <hdegoede@redhat.com>
> ---
>  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. */
> --

Applied as 6.2-rc material, thanks!