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

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Date:	Sun, 04 Aug 2013 09:18:53 +0800
From:	Aaron Lu <aaron.lwe@...il.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
CC:	Felipe Contreras <felipe.contreras@...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 08/03/2013 07:34 PM, Rafael J. Wysocki wrote:
> On Saturday, August 03, 2013 04:14:04 PM Aaron Lu wrote:
>> On 08/03/2013 07:47 AM, Rafael J. Wysocki 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?
>>
>> Yes, the patch is correct, but I still prefer my own version :-)
>> https://github.com/aaronlu/linux/commit/0a3d2c5b59caf80ae5bb1ca1fda0f7bf448b38c9
>>
>> In case you want to take mine and mine needs refresh, please let me know
>> and I can do the re-base, thanks.
> 
> Well, I prefer simpler, unless there's a good reason to use more complicated.
> 
> Why exactly do you think your version is better?

As explained here:
https://lkml.org/lkml/2013/8/2/81
https://lkml.org/lkml/2013/8/2/112

And for the demo broken _BQC, mine patch will disable _BQC while still
make the backlight work, and this patch here is testing the max
brightness level and may fail.

-Aaron
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