linux-kernel - Re: 2.6.31-rc2: thinkpad boots with backlight low

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Message-ID: <20090715223931.GA18924@yamamaya.is-a-geek.org>
Date:	Thu, 16 Jul 2009 00:39:31 +0200
From:	Tobias Diedrich <ranma+kernel@...edrich.de>
To:	Henrique de Moraes Holschuh <hmh@....eng.br>
Cc:	Pavel Machek <pavel@....cz>,
	kernel list <linux-kernel@...r.kernel.org>
Subject: Re: 2.6.31-rc2: thinkpad boots with backlight low

Henrique de Moraes Holschuh wrote:
> There is one thing that comes to mind: display power management.
> 
> Is anything, by chance, setting the backlight devices to low power mode
> on machine restart?  The backlight drivers would try to set brightness
> to 0 when it cannot turn the display off for real...

Whatever registers /sys/class/backlight/thinkpad_screen/ seems to be
responsible.
After boot this has 0 for brightness and actual_brightness, 7 for
max_brightness.
Adjusting the backlight brightness with thinkpad keys does not
affect this at all, it always stays at 0.
If I manually change it to 7 and reboot (or poweroff, for
that matter), then backlight brightness is apparently changed to
that value (instead of minimum).

grepping shows it's actually thinkpad_acpi registering
thinkpad_screen. (Well, that was kind of to be expected)
And /proc/acpi/ibm/brightness also doesn't seem to reflect the real
current value...

What irritates me is that a compiled in thinkpad_acpi does not show
up as a module in /sys/modules and so I can't look at the
module parameters. (brightness_mode looks interesting)

-- 
Tobias						PGP: http://9ac7e0bc.uguu.de
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