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). Regards, Hans
