[ltp] Re: T61 stuck at half brightness if booted on battery power

[Shannon McMackin]

On 09/11/2009 08:02 PM, Marius Gedminas wrote:
> If I reboot my laptop (T61, 6466-55G) while on battery power, the LCD is
> stuck at what feels like the lower half of the brightness range.  I can
> adjust it with xbacklight (or gnome-power-manager) from 0 to 100%, yet
> even at the brightest setting its too dim for comfortable use.  It stays
> so even after I re-plug AC power.
>
> So far the only way I found to restore full brightness is to reboot
> again, which is ... inconvenient, to put it politely.
>
> Where should I start debugging the issue?  AFAIR the BIOS has a setting
> about reducing LCD backlight while on battery power, and AFAIR I have it
> set to keep the same brighness.
>
> I tried searching the list archives and thinkwiki, without much luck.
>
> The kernel is 2.6.28 (latest from Ubuntu's security archive) with
> thinkpad-acpi 0.21.  BIOS version is "7LETA7WW (2.07 )".  This machine
> has Intel video and X.org intel driver is at 2.7.1.  xrandr --properties
> tells me
>
> 	BACKLIGHT_CONTROL:	combination
> 		supported: native       legacy       combination  kernel
> 	BACKLIGHT: 23640 (0x00005c58)	range:  (0,23640)
>
> I can find no trace of any brightness controls in /sys and /proc.
>
> Marius Gedminas
Check your gnome power settings and see what it enforces for battery 
operation.