On 05/15/2014 07:22 PM, Hans de Goede wrote: > 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: Hans de Goede <hdegoede@xxxxxxxxxx> Reviewed-by: Aaron Lu <aaron.lu@xxxxxxxxx> -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
