On Wed, Jun 07, 2023 at 03:39:33PM +0800, AceLan Kao wrote: > What do you think if we unregister backlight devices if the backlight type > is larger than the current registered one. > Do this check in backlight_device_register() and unregister backlight > devices by the order raw(1) > platform(2) > firmware(3) > And maybe introduce a sticky bit into the backlight device if the backlight > driver doesn't want to be removed. Hans looked at doing this, but there were some awkward corner cases. When we first introduced this functionality, firmware was preferred to platform was preferred to raw - but on Intel, at least, this behaviour changed with later versions of Windows. I don't think there's a single static policy that works, I think you need to pay attention to the hints the platform gives you. How does Windows know which interface to use on this platform? The simplest solution may actually just be for dell-laptop to refuse to register a backlight if the platform claims to be Windows 8 or later.
