• Hans de Goede's avatar
    ACPI: video: Add acpi_video_backlight_use_native() helper · 2600bfa3
    Hans de Goede authored
    ATM on x86 laptops where we want userspace to use the acpi_video backlight
    device we often register both the GPU's native backlight device and
    acpi_video's firmware acpi_video# backlight device. This relies on
    userspace preferring firmware type backlight devices over native ones, but
    registering 2 backlight devices for a single display really is undesirable.
    
    On x86 laptops where the native GPU backlight device should be used,
    the registering of other backlight devices is avoided by their drivers
    using acpi_video_get_backlight_type() and only registering their backlight
    if the return value matches their type.
    
    acpi_video_get_backlight_type() uses
    backlight_device_get_by_type(BACKLIGHT_RAW) to determine if a native
    driver is available and will never return native if this returns
    false. This means that the GPU's native backlight registering code
    cannot just call acpi_video_get_backlight_type() to determine if it
    should register its backlight, since acpi_video_get_backlight_type() will
    never return native until the native backlight has already registered.
    
    To fix this add a new internal native function parameter to
    acpi_video_get_backlight_type(), which when set to true will make
    acpi_video_get_backlight_type() behave as if a native backlight has
    already been registered.
    
    And add a new acpi_video_backlight_use_native() helper, which sets this
    to true, for use in native GPU backlight code.
    
    Changes in v2:
    - Replace adding a native parameter to acpi_video_get_backlight_type() with
      adding a new acpi_video_backlight_use_native() helper.
    Acked-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
    Signed-off-by: default avatarHans de Goede <hdegoede@redhat.com>
    2600bfa3
video.h 2.93 KB