Hi, On 10/27/22 14:09, Rafael J. Wysocki wrote: > 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? Right, that can be used as a quick workaround, but we really do want this to work OOTB everywhere. Regards, Hans
