Re: [PATCH] acpi/video: lcd_get_level_current doen't return currentlevel

[Aaron Lu]

On 03/31/2013 04:16 PM, Artem Savkov wrote:
> On Sun, Mar 31, 2013 at 09:04:21AM +0200, Danny Baumann wrote:
> > Hi,
> >
> > Artem Savkov <artem.savkov@xxxxxxxxx> schrieb:
> >
> > > On Sun, Mar 31, 2013 at 08:15:14AM +0200, Danny Baumann wrote:
> > > > Artem Savkov <artem.savkov@xxxxxxxxx> 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.
> >
> > The point is: after the acpi_evaluate_object call, *level must contain the current brightness level, otherwise your BIOS is broken (this happens: e.g. my laptop always returns 100 from _BQC in Windows 8 mode). You can verify this easily by initializing level_current to some invalid value and checking it again after the call to _get_level_current. I'd be pretty surprised if the value didn't change. Also, if you look at [1], you'll see that the code operated on *level before as well.
> > This problem may have been obscured by the fact that the brightness device wasn't initialized properly before my patches went in. Does acpi_video_switch_brightness actually do anything for you when reverting the 3 newest commits of video.c?
>
> Yes, you are right. Both my patch and the version before your patches
> result in initial acpi_video_device_lcd_get_level_current call ending
> with invalid level being returned and bqc disabled, so they both just
> use *level = brightness->curr after that.

OK, this suggests the _BQC control method of your system is broken.
Please kindly file a bug in bugzilla.kernel.org, against
ACPI/Power-Video and attach the output of acpidump and dmidecode there,
I want to take a look, thanks.

-Aaron
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