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

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Message-ID: <CAMP44s0wg2wxWAo9WRXzxxhG_RJ_rfOkPchCoUf7VVradczuqQ@mail.gmail.com>
Date:	Fri, 2 Aug 2013 20:04:52 -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 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.

-- 
Felipe Contreras
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