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

[Marius Gedminas]

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On Fri, Sep 11, 2009 at 09:34:12PM -0400, Shannon McMackin wrote:
> 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.

That is so; I checked now.

>> 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.

> Check your gnome power settings and see what it enforces for battery =20
> operation.

100% screen brightness and no dimming while on battery power.

The slider in g-p-m lets me adjust the brightness the same way as
xbacklight on the console: form black (0%) to dim (100%).  Those
settings are also reflected in xrandr properties as numbers from 0 to
23640.

I rebooted with AC plugged in, went into the BIOS, checked the backlight
setting, used Fn+Home to make the screen bright again, booted Ubuntu.
Now the xbacklight range is twice as wide.  xrandr --properties still
shows the same range numbers (0,23640).

Marius Gedminas
--=20
I've been in the sun for a week.  I took the bold step of leaving my
laptop at home.  I found only 4K messages pending when I returned.
        -- Keith Packard

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