linux-kernel - Re: [PATCH] acpi/video: lcd_get_level_current doen't return current level

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Message-ID: <20130331064619.GA11544@thinkpad.lan>
Date:	Sun, 31 Mar 2013 10:46:19 +0400
From:	Artem Savkov <artem.savkov@...il.com>
To:	Danny Baumann <dannybaumann@....de>
Cc:	aaron.lu@...el.com, rafael.j.wysocki@...el.com,
	linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] acpi/video: lcd_get_level_current doen't return current
 level

On Sun, Mar 31, 2013 at 08:15:14AM +0200, Danny Baumann wrote:
> Artem Savkov <artem.savkov@...il.com> schrieb:
> >acpi_video_device_lcd_get_level_current() called
> >acpi_video_bqc_value_to_level()
> >with "*level" as a second argument, resulting in level being returned
> >based on
> >initial input, not current brightness, breaking backlight controls.
> I don't think this change is correct. As level was passed as parameter into the evaluation of _BQC, *level contains the AML returned brightness level afterwards, so it's correct to use it as an input to acpi_video_bqc_value_to_level(). Actually, the whole point of acpi_video_device_lcd_get_level_current() is to update device->brightness->curr, so it doesn't make sense to me to use it in that function.
> 
> What's the exact problem this patch tries to solve?

I'm running a -next kernel on my laptop and couple of days ago keyboard
backlight controls stopped working: only 2 lower brightness levels. I've
debugged it a bit and found out that acpi_video_switch_brightness() calls
acpi_video_device_lcd_get_level_current() with level uninitialized and
always gets lowest posible value.

-- 
Regards,
Artem
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