linux-kernel - Re: acpi 'video' driver, and issues with 'brightness_switch

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Date:	Tue, 28 Apr 2009 10:43:24 +0800
From:	Zhang Rui <rui.zhang@...el.com>
To:	Maxim Levitsky <maximlevitsky@...il.com>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>
Subject: Re: acpi 'video' driver, and issues with
	'brightness_switch_enabled=0'

On Tue, 2009-04-28 at 01:57 +0800, Maxim Levitsky wrote:
> I have a notebook which handles brightness keys in hardware, but tells
> loudly when it does so.
> 
if you boot into console mode w/o ACPI video driver, does the brightness
still change when you press the hotkeys?

> Currently, acpi 'video' also sets the brightness, which result in double
> setting, and on top of that it emits a key that makes gpm set brightness
> again.
> 
we need to support the brightness control in console mode.
and "brightness_switch_enabled" should be cleared in graphics mode to
prevent the ACPI video driver action upon hotkey events.

> And (yes...) on top of that keyboard emits a brightness up/down even,
> which (you guessed...) sets brightness again.
> 
> I found out that it is possible to tell gnome-power-manager not to set
> brightness, but yet in kernel driver still sets it.
> 
> I found out even earlier that I can use brightness_switch_enabled=0,
> which supposed to make inkernel driver not touch the brightness.
> But I found out that this driver won't update the brightness, in /sys
> interface when I set this param.
> 
No, when "brightness_switch_enabled" is cleared, gdm should still use
the ACPI backlight sysfs I/F if available to change the backlight,
i.e. /sys/class/backlight/acpi_video0/...

what's the model name of your laptop?
are you using Intel graphics?
please attach the output of acpidump and lspci.
It would be great if you can file a bug report about this issue at
bugzilla.kernel.org.

thanks,
rui

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