Message-ID: <CAMP44s3z7M9omEkc23JNuVpCAKi=gqdBCThCdBcBrW-QYpuzkg@mail.gmail.com>
Date:	Tue, 30 Jul 2013 21:07:44 -0500
From:	Felipe Contreras <felipe.contreras@...il.com>
To:	Aaron Lu <aaron.lwe@...il.com>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>, linux-kernel@...r.kernel.org,
	linux-acpi@...r.kernel.org, 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 Tue, Jul 30, 2013 at 8:36 PM, Aaron Lu <aaron.lwe@...il.com> wrote:
> On 07/31/2013 08:11 AM, Felipe Contreras wrote:
>> On Tue, Jul 30, 2013 at 6:13 PM, Rafael J. Wysocki <rjw@...k.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.

File a bug where?

>> 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?

No, setting level 0 turns it off if efaa14c is *not* reverted. In 3.10
0 doesn't turn it off.

>> 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.

I looked at the code in the DCDT, it appears to me that they store
different levels depending on the OSI version, so I don't think the
problem is in the ACPI driver. Yet, the issue remains there.

-- 
Felipe Contreras
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