Message-ID: <51F86A20.3060309@gmail.com>
Date: Wed, 31 Jul 2013 09:36:32 +0800
From: Aaron Lu <aaron.lwe@gmail.com>
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To: Felipe Contreras <felipe.contreras@gmail.com>
CC: "Rafael J. Wysocki" <rjw@sisk.pl>, linux-kernel@vger.kernel.org,
        linux-acpi@vger.kernel.org, Len Brown <lenb@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [REGRESSION/PATCH] acpi: blacklist win8 OSI for ASUS Zenbok Prime
 UX31A
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On 07/31/2013 08:11 AM, Felipe Contreras wrote:
> On Tue, Jul 30, 2013 at 6:13 PM, Rafael J. Wysocki <rjw@sisk.pl> wrote:
> 
>>> If 0 turns the screen off with the intel driver, 0 should turn the
>>> screen off with the ACPI driver, having inconsistent behavior
>>> depending on which driver is used is a bug.
>>
>> The ACPI driver simply exposes and interface to interact with the AML methods
>> in the BIOS directly.
> 
> No, the ACPI driver is exposing a backlight interface, which has a
> defined stable API.
> 
> Documentation/ABI/stable/sysfs-class-backlight
> 
> Yes, the interface doesn't define what should happen at 0, that is a
> bug in the interface definition.
> 
> *How* it achieves that is an implementation detail.
> 
>> Yes, this is a mistake and shouldn't be designed this way.
>>
>> However, incidentally, this makes backlight control work on your machine.
>>
>> Anyway, we need all backlight drivers to work consistently and don't tempt me
>> to rip the ACPI driver entirely from the kernel for what it's worth.
> 
> Yes, they should work consistently, and go ahead, rip the ACPI driver,
> *then* you'll see many more people complaining about the Linux kernel
> breaking user-space, which should never happen. Mistakes happen, but
> if you do this willingly and knowingly, I think there would be
> repercussions for you.
> 
>> Yes, that will break backlight on your system and *then* you can complain to
>> Linus if you wish.
> 
> It is already broken in v3.11-rc3, in fact I just booted that to try
> it out and it booted with the screen completely black (fortunately I
> knew exactly what to type to change that).

That is bad, can you please file a bug for that? I'll need to take a
look at your ACPI tables, thanks.

> 
> Apparently this commit also needs to be reverted: efaa14c (ACPI /
> video: no automatic brightness changes by win8-compatible firmware).
> In this machine it makes the backlight work again (without
> acpi_osi="!Windows 2012"), but by doing so the ACPI driver also turns
> off the screen completely at level 0. Also, each time I change the

So with rc3 and commit efaa14c reverted, when you set level 0 to ACPI
video's backlight interface, the screen will be off now? And this is not
the case in 3.10, right?

> backlight level from X, the screen blinks as if going 100%, 0%, and
> then the desired level.

Please attach acpidump output to the to be opened bugzilla page, thanks.

-Aaron

> 
> For this particular machine simply applying the attached patch would
> solve all those regressions, but who knows in other machines, I think
> it's safer to revert efaa14c.
> 

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