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

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Message-ID: <2595035.fPqa5yE0N9@vostro.rjw.lan>
Date:	Sat, 03 Aug 2013 03:19:04 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Felipe Contreras <felipe.contreras@...il.com>
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 Friday, August 02, 2013 08:07:37 PM Felipe Contreras wrote:
> On Fri, Aug 2, 2013 at 8:16 PM, Rafael J. Wysocki <rjw@...k.pl> wrote:
> > On Friday, August 02, 2013 08:04:52 PM Felipe Contreras wrote:
> >> On Fri, Aug 2, 2013 at 6:47 PM, Rafael J. Wysocki <rjw@...k.pl> wrote:
> >> > On Friday, August 02, 2013 02:37:09 PM Felipe Contreras wrote:
> >> >> If the _BCL package is descending, the first level (br->levels[2]) will
> >> >> be 0, and if the number of levels matches the number of steps, we might
> >> >> confuse a returned level to mean the index.
> >> >>
> >> >> For example:
> >> >>
> >> >>   current_level = max_level = 100
> >> >>   test_level = 0
> >> >>   returned level = 100
> >> >>
> >> >> In this case 100 means the level, not the index, and _BCM failed. But if
> >> >> the _BCL package is descending, the index of level 0 is also 100, so we
> >> >> assume _BQC is indexed, when it's not.
> >> >>
> >> >> This causes all _BQC calls to return bogus values causing weird behavior
> >> >> from the user's perspective. For example: xbacklight -set 10; xbacklight
> >> >> -set 20; would flash to 90% and then slowly down to the desired level
> >> >> (20).
> >> >>
> >> >> The solution is simple; test anything other than the first level (e.g.
> >> >> 1).
> >> >>
> >> >> Signed-off-by: Felipe Contreras <felipe.contreras@...il.com>
> >> >
> >> > Looks reasonable.
> >> >
> >> > Aaron, what do you think?
> >>
> >> Aaron has a similar patch does many more checks. I think we should add
> >> more checks, but I think those should go into a separate patch.
> >>
> >> This patch alone fixes a real problem, which is rather urgent to fix,
> >> and I did it this way so it's trivial to review and merge.
> >
> > And I still would like to know the Aaron's opinion, what's wrong with that?
> 
> Nothing. What's wrong with my clarification?

You're not Aaron. :-)

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