linux-kernel - Re: [REGRESSION/PATCH] acpi: blacklist win8 OSI for ASUS Zenbok Prime UX31A

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Message-ID: <51F755E3.8040706@gmail.com>
Date:	Tue, 30 Jul 2013 13:57:55 +0800
From:	Aaron Lu <aaron.lwe@...il.com>
To:	Felipe Contreras <felipe.contreras@...il.com>
CC:	linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
	"Rafael J. Wysocki" <rjw@...k.pl>, Len Brown <lenb@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [REGRESSION/PATCH] acpi: blacklist win8 OSI for ASUS Zenbok Prime
 UX31A

On 07/30/2013 01:51 PM, Aaron Lu wrote:
> On 07/30/2013 11:44 AM, Felipe Contreras wrote:
>> On Mon, Jul 29, 2013 at 10:11 PM, Aaron Lu <aaron.lwe@...il.com> wrote:
>>> On 07/30/2013 03:20 AM, Felipe Contreras wrote:
>>>> Since v3.7 the acpi backlight driver doesn't work at all on this machine
>>>> because presumably the ACPI code contains stub code when Windows 8 OSI is
>>>> reported.
>>>>
>>>> The commit ea45ea7 (in v3.11-rc2) tried to fix this problem by using the intel
>>>> backlight driver, however, on this machine it turns the backlight completely
>>>> off when it reaches level 0%, after which the user might have a lot trouble
>>>> trying to bring it back.
>>>
>>> What do you mean by a lot of trouble? If you press hotkey to increase
>>> backlight brightness level, does it work?
>>
>> I guess so, *if* there is indeed a user-space power manager handling
>> that, *and* the keyboard has such keys, *or* the user has set custom
>> hotkeys.
> 
> Right, for a GUI environment this may not be a big problem(user uses Fn
> key to decrease brightness level and then hit the black screen, it's
> natural he will use Fn key to increase brightness level).
> 
>>
>>> If so, the screen should not
>>> be black any more, it's not that user has to blindly enter some command
>>> to get out of the black screen.
>>>
>>> And I'm not sure if this is a bug of intel_backlight(setting a low level
>>> makes the screen almost off), I see different models with different
>>> vendors having this behavior.
>>
>> I mean, the screen is completely off, I cannot see absolutely
>> anything. I don't see this behavior with the ACPI backlight driver,
>> nor do I see that in Windows 7.
>>
>>> If this is deemed a bug, then I'm afraid
>>> intel_backlight interface is useless for a lot of systems...perhaps we
>>> can only say, intel_backlight's interpretation of low levels are
>>> different with ACPI video's, and that's probably why its type is named
>>> as raw :-)
>>
>> Well, a bug is defined as unexpected behavior -- as a user, if I'm
>> changing the brightness of the screen, I certainly don't expect the
>> screen to turn off, and I think that's the expectation from most
>> people. It's the first time I see something like that.
> 
> I agree this is kind of un-expected. At the same time, this seems to be
> the normal behavior for intel_backlight. I don't know what the correct
> thing to do here if this is something we want to avoid - modify intel
> backlight handling code not to set too low value or change the user
> space tool not to set a too low value if they are interacting with a
> raw type interface. Neither of them sounds cool... Or, users may get
> used to it, I for example, don't find this to be very annoying, but
> maybe I'm already used to it.

BTW, for the complete screen off problem, I don't see there is anything
wrong with it from code's point of view. It's not that there is an error
in code or this is a broken hardware that caused the screen off when
setting a very low or 0 brightness level, it is simply the expected
behavior of what this interface can provide. It can really set the
brightness level to minimum(zero) or maximum. Don't get me wrong, I
didn't mean this is a good user experience, I don't know that. I just
don't think this is a program bug, and I don't know if this should be
fixed or not - obviously this interface did what it is asked to do,
correctly.

Thanks,
Aaron
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