Created attachment 122191 [details]
My laptop (Aspire V5-431) gets an acpi_video0 entry in /sys/class/backlight/
that is not working, alongside an intel_backlight entry that *is* working.
I see the following entry in the kernel log:
[ 19.515016] acer_wmi: Brightness must be controlled by acpi video driver
By using 'acpi_backlight=vendor' acpi_video0 disappears.
See the bug report on the linux-acpi mailing list:
The backlight control provided by ACPI is through EC, while for this laptop model it's obvious the backlight control circuit is not routed to EC, so the ACPI interface is not usable.
Please attach your DMI info:
# dmidecode > dmi.txt
Created attachment 122381 [details]
As per requested
Does add video.use_native_backlight=1 to kernel cmdline help? Please test this kernel cmdline on a v3.13 kernel.
$ dmesg | grep backlight
[ 0.000000] Command line: BOOT_IMAGE=/boot/vmlinuz-3.13.0-031300-generic root=UUID=4cfdb2ed-677a-4fd0-aa7d-5b118700bd35 ro quiet splash video.use_native_backlight=1 vt.handoff=7
[ 0.000000] Kernel command line: BOOT_IMAGE=/boot/vmlinuz-3.13.0-031300-generic root=UUID=4cfdb2ed-677a-4fd0-aa7d-5b118700bd35 ro quiet splash video.use_native_backlight=1 vt.handoff=7
$ uname -a
Linux thomasc-Aspire-V5-431 3.13.0-031300-generic #201401192235 SMP Mon Jan 20 03:36:48 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux
OK, so this is another Win8 firmware compatible problem.
*** This bug has been marked as a duplicate of bug 51231 ***