Created attachment 112341 [details]
Lenovo Yoga 13 ACPI dump
I have a problem very similar to bug 51231, but on a Lenovo Yoga 13. The brightness keys in X do not change the backlight. Booting with normal kernel options results in two entries in /sys/class/backlight: acpi_video0 and intel_backlight. acpi_video0 has no effect on the brightness, but intel_backlight does. When the brightness keys are pressed, X is changing the acpi_video0 brightness.
Booting with acpi_osi="!Windows 2012" does not seem to make a difference. Booting with acpi_backlight=vendor creates:
ideapad -> ../../devices/platform/ideapad/backlight/ideapad
intel_backlight -> ../../devices/pci0000:00/0000:00:02.0/drm/card0/card0-LVDS-1/intel_backlight
instead of acpi_video0. This one does not work either. (intel_backlight still works).
ACPI dump output is attached. I am glad to try patches, boot options, etc.
I tried v5 of the patch series attached to bug 51231 on 3.12.0-rc5 on my Yoga, and can verify that booting with video.use_native_backlight=1 corrects the problem. (At first glance, I thought the patch series only fixed the problem for models using the thinkpad driver, so didn't look into it.) acpi_video0 does not appear, and so X uses intel_backlight instead.
This is good enough for me to consider the issue resolved, but I'm still glad to test out any changes.
I'll add Yoga 13 into a quirk table to skip register ACPI video's backlight interface for it, so no cmdline option is needed.
*** This bug has been marked as a duplicate of bug 51231 ***