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

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Date:	Tue, 30 Jul 2013 13:51:40 +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 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.

-Aaron
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