@@ -844,6 +844,27 @@ enum acpi_backlight_type __acpi_video_get_backlight_type(bool native, bool *auto
if (native_available)
return acpi_backlight_native;
+ /*
+ * The vendor specific BIOS interfaces are only necessary for
+ * laptops from before ~2008.
+ *
+ * For laptops from ~2008 till ~2023 this point is never reached
+ * because on those (video_caps & ACPI_VIDEO_BACKLIGHT) above is true.
+ *
+ * Laptops from after ~2023 no longer support ACPI_VIDEO_BACKLIGHT,
+ * if this point is reached on those, this likely means that
+ * the GPU kms driver which sets native_available has not loaded yet.
+ *
+ * Returning acpi_backlight_vendor in this case is known to sometimes
+ * cause a non working vendor specific /sys/class/backlight device to
+ * get registered.
+ *
+ * Return acpi_backlight_none on laptops with ACPI tables written
+ * for Windows 8 (laptops from after ~2012) to avoid this problem.
+ */
+ if (acpi_osi_is_win8())
+ return acpi_backlight_none;
+
/* No ACPI video/native (old hw), use vendor specific fw methods. */
return acpi_backlight_vendor;
}
There have been 2 separate reports now about a non working "dell_backlight" device getting registered under /sys/class/backlight 1 report for a Raptor Lake based Dell and 1 report for a Meteor Lake (development) platform. On hw from the last 10 years dell-laptop will not register "dell_backlight" because acpi_video_get_backlight_type() will return acpi_backlight_video there if called before the GPU/kms driver loads. So it does not matter if the GPU driver's native backlight is registered after dell-laptop loads. But it seems that on the latest generation laptops the ACPI tables no longer contain acpi_video backlight control support which causes acpi_video_get_backlight_type() to return acpi_backlight_vendor causing "dell_backlight" to get registered if the dell-laptop module is loaded before the GPU/kms driver. Vendor specific backlight control like the "dell_backlight" device is only necessary on quite old hw (from before acpi_video backlight control was introduced). Work around "dell_backlight" registering on very new hw (where acpi_video backlight control seems to be no more) by making acpi_video_get_backlight_type() return acpi_backlight_none instead of acpi_backlight_vendor as final fallback when the ACPI tables have support for Windows 8 or later (laptops from after ~2012). Suggested-by: Matthew Garrett <mjg59@srcf.ucam.org> Reported-by: AceLan Kao <acelan.kao@canonical.com> Closes: https://lore.kernel.org/platform-driver-x86/20230607034331.576623-1-acelan.kao@canonical.com/ Signed-off-by: Hans de Goede <hdegoede@redhat.com> --- drivers/acpi/video_detect.c | 21 +++++++++++++++++++++ 1 file changed, 21 insertions(+)