• Hans de Goede's avatar
    ACPI / video: Add an acpi_video_unregister_backlight function · 1b7f37e1
    Hans de Goede authored
    Add an acpi_video_unregister_backlight function, which only unregisters
    the backlight device, and leaves the acpi_notifier in place. Some acpi_vendor
    driver need this as they don't want the acpi_video# backlight device, but do
    need the acpi-video driver for hotkey handling.
    
    Chances are that this new acpi_video_unregister_backlight() is actually
    what existing acpi_vendor drivers have wanted all along. Currently acpi_vendor
    drivers which want to disable the acpi_video# backlight device, make 2 calls:
    
    acpi_video_dmi_promote_vendor();
    acpi_video_unregister();
    
    The intention here is to make things independent of when acpi_video_register()
    gets called. As acpi_video_register() will get called on acpi-video load time
    on non intel gfx machines, while it gets called on i915 load time on intel
    gfx machines.
    
    This leads to the following 2 interesting scenarios:
    
     a) intel gfx:
      1) acpi-video module gets loaded (as it is a dependency of acpi_vendor
         and i915)
      2) acpi-video does NOT call acpi_video_register()
      3) acpi_vendor loads (lets assume it loads before i915), calls
         acpi_video_dmi_promote_vendor(); which sets
         ACPI_VIDEO_BACKLIGHT_DMI_VENDOR
      4) calls acpi_video_unregister -> not registered, nop
      5) i915 loads, calls acpi_video_register
      6) acpi_video_register registers the acpi_notifier for the hotkeys,
         does NOT register a backlight device because of
         ACPI_VIDEO_BACKLIGHT_DMI_VENDOR
    
     b) non intel gfx
      1) acpi-video module gets loaded (as it is a dependency acpi_vendor)
      2) acpi-video calls acpi_video_register()
      3) acpi_video_register registers the acpi_notifier for the hotkeys,
         and a backlight device
      4) acpi_vendor loads, calls acpi_video_dmi_promote_vendor()
      5) calls acpi_video_unregister, this unregisters BOTH the acpi_notifier
         for the hotkeys AND the backlight device
    
    So here we have possibly the same acpi_vendor module, making the same calls,
    but with different results, in one cases acpi-video does handle hotkeys,
    in the other it does not.
    
    Note that the a) scenario turns into b) if we assume the i915 module loads
    before the vendor_acpi module, so we also have different behavior depending
    on module loading order!
    
    So as said I believe that quite a few existing acpi_vendor modules really
    always want the behavior of a), hence this patch adds a new
    acpi_video_unregister_backlight() which gives the behavior of a) independent
    of module loading order.
    Signed-off-by: default avatarHans de Goede <hdegoede@redhat.com>
    Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
    1b7f37e1
video.h 1.05 KB