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

[Marius Gedminas]

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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     =20
	BACKLIGHT: 23640 (0x00005c58)	range:  (0,23640)

I can find no trace of any brightness controls in /sys and /proc.

Marius Gedminas
--=20
Favorite MS-DOS error message: "Drive C: not ready, close door."

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