Kernel Bug Tracker – Bug 16036
_BCM doesn't work (writing to EC BLVL but no effect) - Toshiba T130
Last modified: 2010-09-29 01:55:26 UTC
Created attachment 26510 [details]
When changing brightness using xbacklight or e.g. echo "3" > /sys/class/backlight/acpi_video0/brightness the values in /sys/class/backlight/acpi_video0/actual_brightness and /proc/acpi change, but the actual backlight brightness does not change.
Created attachment 26530 [details]
do you have a windows partition on this laptop?
If yes, it would be great if you can verify if the backlight control works in windows or not.
In windows I'm able to modify the brightness. Furthermore, the DSDT tables are exactly the same for Windows7 and Linux, if this is of any help to you. Please tell me if I can be of any help to solve this problem!
are you using windows XP, Vista or win7?
I tried with windows 7.
please rebuild the kernel with CONFIG_ACPI_WMI=y, and boot with acpi_backlight=vendor.
can the backlight work in this case?
The backlight also doesn't work with this setting in both kernel-2.6.34 and current 2.6.35 git (commit 980019d74e4b2428362b36a0506519d6d9460800). Both dmesg logs are attached along with the 2.6.35 config file.
Created attachment 26990 [details]
dmesg for 2.6.34 boot
Created attachment 26991 [details]
dmesg for 2.6.35 boot
Created attachment 26992 [details]
config for 2.6.35
Any progress here ?
2.6.35 kernel (ubuntu): CONFIG_ACPI_WMI=y
booting with or without acpi_backlight=vendor - backlight is not controllable.
It worked before with "nomodeset acpi_backlight=vendor" (ubuntu 10.04 / kernel 2.6.32, xorg 1.7.6), but with newer xorg (1.9.0) it is not an option.
Preinstalled win7 works OK.
sudo setpci -s 00:02.0 F4.B=80
like approach works anyway. Because it doesn't use ACPI ?
From the acpidump it seems that there exists the _BCM/_BCL/_BQC object. But after the _BCM object will write the requested brightness level to EC register, the brightness can't be changed. Maybe this is related with the BIOS.
When writing the value to IGD PCI config space, it will write the IGD graphics backlight register. Maybe the incorrect ACPI backlight control mechanism is exported on this box.
*** This bug has been marked as a duplicate of bug 14216 ***