Screen brightness is unresponsive to Fn+F7 and Fn+F8 key presses, however the values in the following paths do change accordingly:
I found an error message in /var/log/messages which may be a bug in the kernel module drivers/acpi/video.ko
[Firmware Bug]: ACPI: ACPI brightness control misses _BQC function
The laptop uses Intel GMA 4500MHD.
Please advise what information / output you require to debug this issue.
please attach the acpidump output of this laptop.
Created attachment 25720 [details]
output of acpidump
please set CONFIG_ACPI_WMI and see if it helps.
(In reply to comment #3)
> please set CONFIG_ACPI_WMI and see if it helps.
In the current (Ubuntu 2.6.32-17-generic) kernel it's already set:
I'm not sure if this will help, but I had a look in the kernel source and found comments which may possibly be related to the "ACPI brightness control misses _BQC function" message I get in dmesg.
In drivers/acpi/video.c there is a comment regarding _BCQ as opposed to _BQC which says:
/* Some buggy BIOS uses _BCQ instead of _BQC */
which appears in the acpi_video_device_cap struct.
Could it be likely this BIOS may be doing similar?
My current kernel is now 2.6.32-22-generic. Unfortunately the problem remains. Is there an update to this problem? It's been a while.
I found the fix here:
Technically it addressed a fault with brightness functionality for a Dell Studio 1558, however once I installed the two .deb files as directed (and rebooted), the brightness function worked.
Kamal stated this was a preliminary test fix. It'd be good to have it progress to be integrated with the next kernel release. As he suggested, it's for '...Dell Studios or any other i915-based systems."
On 2nd thought, since he released 3 patches, I'll mark this as RESOLVED PATCH_ALREADY_AVAILABLE