Re: [PATCH] acpi: video: improve quirk check

["Rafael J. Wysocki" <rjw@sisk.pl>]

On Sunday, August 04, 2013 01:42:49 AM Felipe Contreras wrote:
> On Sat, Aug 3, 2013 at 8:18 PM, Aaron Lu <aaron.lwe@gmail.com> wrote:
> > 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@gmail.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.
> 
> Yes, but that problem can *only* happen in such a simplified _BCL,
> which is very very unlikely. Still, it would make sense to fix the
> code for that case.

Yes, it would.

> However, we can fix the problem first for the real known cases with my
> simple one-liner patch that can even be merged for v3.11, and *later*
> fix the issue for the synthetic unlikely case.

If we're going to fix it in 3.12, it's good to discuss it now, which is why
I'm askig about that.

> 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)?

Rafael