The only way to make the backlight for the Intel GMA 4500M working in Xorg, is to set the 'Backlight' device option to 'intel_backlight'. In BUG#35072, Daniel Vetter said that this should be blacklisted from ACPI since the userspace driver will pick the intel backlight.
the real problem to me is why acpi_video0 does not work. what is the model of your laptop? can you please attach the acpidump output of your laptop? if you poke /sys/class/video/, the intel_backlight one can change the real backlight, right? how about the acpi_video0?
Created attachment 86371 [details] acpidump output This is the output of acpidump. echo "3" > /sys/class/backlight/acpi_vendor0/brightness does nothing.
(In reply to comment #1) > the real problem to me is why acpi_video0 does not work. > what is the model of your laptop? Toshiba T130-15T
please attach the dmidecode of your laptop.
Created attachment 88161 [details] dmidecode output
Hi Andrea, Did you boot with any acpi_osi= param? In the acpi table, I don't see any problem, except the set brightness level control method _BCM will only do things if the OS is windows 2006: Store (0xBB, P80H) If (LEqual (OSYS, 0x07D6)) { Store (0xBC, P80H) Acquire (^^^LPCB.EC0.MUT1, 0xFFFF) Store (Local1, ^^^LPCB.EC0.BLVL) Release (^^^LPCB.EC0.MUT1) } But if there is no acpi_osi kernel command line, linux will respond as a windows 2006 system, so should just work.
Hi, I've no acpi_osi param set. Command line: ../vmlinuz-linux ../vmlinuz-linux root=/dev/sda6 ro rootfstype=ext4 initrd=../initramfs-linux.img
I'm using 3.8.2 and setting "Backlight" to "intel_backlight" is the only way to workaround this
Thanks Andrea. So it seems the BIOS table is broken, it can't handle brightness level. You can add acpi_backlight=vendor to kernel command line to make acpi video driver stop creating the sysfs interface /sys/class/backlight/acpi_video0.
Uhm, no. Doesn't work that way neither.
Please list directory of /sys/class/backlight after you added the acpi_backlight=vendor kernel command line, thanks.
% ls /sys/class/backlight intel_backlight toshiba
(In reply to comment #12) > % ls /sys/class/backlight > intel_backlight toshiba Are you using gnome? I know that gnome-settings-daemon has the following preference regarding backlight control interface: firmware -> platform -> raw while acpi's interface is of type firmware, and platform driver(toshiba in your case)'s is of type platform and graphics driver's is of type raw. So this means toshiba's acpi driver can not handle your backlight either, and I don't know if there is an option to disable platform driver's interface. I'm afraid you'll need to take advantage of your GUI's setting ability to choose the right backlight interface to use(intel_backlight in this case).
No, I'm using KDE. Anyway, ff there's no issue with the current kernel about this you can close it. I'll keep the xorg option to use the right backlight driver.
BIOS table problem, close as WILL_NOT_FIX.