On Thu, Oct 27, 2022 at 11:39:38AM +0200, Hans de Goede wrote: > The *only* behavior which actually is new in 6.1 is the native GPU > drivers now doing the equivalent of: > > if (acpi_video_get_backlight_type() != acpi_backlight_native) > return; > > In their backlight register paths (i), which is causing the native > backlight to disappear on your custom laptop setup and on Chromebooks > (with the Chromebooks case being already solved I hope.). It's causing the backlight control to vanish on any machine that isn't ((acpi_video || vendor interface) || !acpi). Most machines that fall into that are either weird or Chromebooks or old, but there are machines that fall into that. (I wrote https://mjg59.livejournal.com/127103.html over 12 years ago, so please do assume that I'm familiar with the complexities here :) ) > I agree this is a possible solution if this turns out to break more > systems and there is no other easy/clean way to fix those. But I would > greatly prefer to keep this change and stop the IMHO bad kernel behavior > of "registering multiple backlight-devices for a single panel and then > let userspace sort it out". If we're not able to make a correct policy decision in the kernel then punting it to userland seems like the right thing to do? The kernel absolutely *should* make the right decision where it has enough information to do so, but in this case the code that's making that decision doesn't have the full set of information.
