linux-kernel - Re: [PATCH] acpi: video: improve quirk check

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Date:	Sun, 4 Aug 2013 09:19:56 -0500
From:	Felipe Contreras <felipe.contreras@...il.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Aaron Lu <aaron.lwe@...il.com>, linux-kernel@...r.kernel.org,
	linux-acpi@...r.kernel.org, Len Brown <lenb@...nel.org>,
	Zhang Rui <rui.zhang@...el.com>
Subject: Re: [PATCH] acpi: video: improve quirk check

On Sun, Aug 4, 2013 at 9:19 AM, Rafael J. Wysocki <rjw@...k.pl> wrote:
> On Sunday, August 04, 2013 01:42:49 AM Felipe Contreras wrote:

>> Personally I think there are better ways to fix the code for the
>> synthetic case than what you patch does, which will also make _BQC
>> work. That can be discussed later though, the one-liner is simple, and
>> it works.
>
> So, let's assume that the one-liner goes into 3.11 and work further with that
> assumption.
>
> How would you address the sythetic case (on top of the one-liner)?

I would write and read two values instead of one. The code is trying
to check if _BQC is always returning the maximum, and if you try with
two values you can be absolutely certain if that's happening or not;
it doesn't even matter which values you choose. Even in the synthetic
case that only has two values the check would work correctly and
detect that _BQC works correctly (or not).

In my machine I think the issue is slightly different, I think _BCM is
failing, at least until enabling the _DOS thing, but at the end of the
day it's the same thing for the check; _BQC is always returning the
same value, and the code above will find that out, regardless of which
values are tested.

For my particular machine though, I think it's more interesting to
find out why _BCM is failing before _DOS, and why efaa14c made it
work. If that is actually the case.

-- 
Felipe Contreras
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