On Thu, Oct 27, 2022 at 12:37 PM Hans de Goede <hdegoede@xxxxxxxxxx> wrote: > > Hi, > > On 10/27/22 11:52, Matthew Garrett wrote: > > 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 acknowledge that their are machines that fall into this category, > but I expect / hope there to be so few of them that we can just DMI > quirk our way out if this. > > I believe the old group to be small because: > > 1. Generally speaking the "native" control method is usually not > present on the really old (pre ACPI video spec) mobile GPUs. > > 2. On most old laptops I would still expect there to be a vendor > interface too, and if both get registered standard desktop environments > will prefer the vendor one, so then we need a native DMI quirk to > disable the vendor interface anyways and we already have a bunch of > those, so some laptops in this group are already covered by DMI quirks. > > And a fix for the Chromebook case is already in Linus' tree, which > just leaves the weird case, of which there will hopefully be only > a few. > > I do share your worry that this might break some machines, but > the only way to really find out is to get this code out there > I'm afraid. > > I have just written a blog post asking for people to check if > their laptop might be affected; and to report various details > to me of their laptop is affected: > > https://hansdegoede.dreamwidth.org/26548.html > > Lets wait and see how this goes. If I get (too) many reports then > I will send a revert of the addition of the: > > if (acpi_video_get_backlight_type() != acpi_backlight_native) > return; > > check to the i915 / radeon / amd / nouveau drivers. > > (And if I only get a couple of reports I will probably just submit > DMI quirks for the affected models). Sounds reasonable to me, FWIW. And IIUC the check above can be overridden by passing acpi_backlight=native in the kernel command line, right?
