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

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Date:	Mon, 29 Jul 2013 22:44:19 -0500
From:	Felipe Contreras <felipe.contreras@...il.com>
To:	Aaron Lu <aaron.lwe@...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 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.

> 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.

-- 
Felipe Contreras
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