acpi_video_unregister() not only unregisters the acpi-video backlight interface but also unregisters the acpi video bus event listener, causing e.g. brightness hotkey presses to no longer generate keypress events.
The unregistering of the acpi video bus event listener usually is undesirable, which by itself is a good reason to switch to acpi_video_unregister_backlight().
Another problem with using acpi_video_unregister() rather then using acpi_video_unregister_backlight() is that on systems with an intel video opregion (most systems) whether or not the acpi video bus event listener actually gets unregistered depends on module load ordering:
Scenario a: 1) acpi/video.ko gets loaded (*), does not do acpi_video_register as there is an intel opregion. 2) intel.ko gets loaded, calls acpi_video_register() which registers both the listener and the acpi backlight interface 3) apple-gmux.ko gets loaded, calls acpi_video_unregister() causing both the listener and the acpi backlight interface to unregister
Scenario b: 1) acpi/video.ko gets loaded (*), does not do acpi_video_register as there is an intel opregion. 2) apple-gmux.ko gets loaded, calls acpi_video_dmi_promote_vendor(), calls acpi_video_unregister(), which is a nop since acpi_video_register has not yet been called 2) intel.ko gets loaded, calls acpi_video_register() which registers the listener, but does not register the acpi backlight interface due to the call to the preciding call to acpi_video_dmi_promote_vendor()
*) acpi/video.ko always loads first as both other modules depend on it.
So we end up with or without an acpi video bus event listener depending on module load ordering, not good.
Switching to using acpi_video_unregister_backlight() means that independ of ordering we will always have an acpi video bus event listener fixing this.
Note that this commit means that systems without an intel video opregion, and systems which were hitting scenario a wrt module load ordering, are now getting an acpi video bus event listener while before they were not!
On some systems this may cause the brightness hotkeys to start generating keypresses while before they were not (good), while on other systems this may cause the brightness hotkeys to generate multiple keypress events for a single press (not so good). Since on most systems the acpi video bus is the canonical source for brightness events I believe that the latter case will needs to be handled on a case by case basis by filtering out the duplicate keypresses at the other source for them.
Cc: Seth Forshee seth.forshee@canonical.com Signed-off-by: Hans de Goede hdegoede@redhat.com --- drivers/platform/x86/apple-gmux.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/platform/x86/apple-gmux.c b/drivers/platform/x86/apple-gmux.c index 6808715..45032ce 100644 --- a/drivers/platform/x86/apple-gmux.c +++ b/drivers/platform/x86/apple-gmux.c @@ -551,7 +551,7 @@ static int gmux_probe(struct pnp_dev *pnp, const struct pnp_device_id *id) * Disable the other backlight choices. */ acpi_video_dmi_promote_vendor(); - acpi_video_unregister(); + acpi_video_unregister_backlight(); apple_bl_unregister();
gmux_data->power_state = VGA_SWITCHEROO_ON;