Re: Question about ACPI Video

[Zhang Rui <rui.zhang@intel.com>]

On Thu, 2010-01-28 at 02:02 +0800, Edward Shao wrote:
> On Tue, Jan 26, 2010 at 8:58 AM, Zhang Rui <rui.zhang@intel.com> wrote:
> > On Mon, 2010-01-25 at 17:45 +0800, luke lin wrote:
> >> Hi all,
> >>
> >> I read the drivers/acpi/video.c:
> >>
> >> 895         result = acpi_video_device_lcd_set_level(device, max_level);
> >> 896         if (result)
> >> 897                 goto out_free_levels;
> >> 898
> >> 899         result = acpi_video_device_lcd_get_level_current(device, &level);
> >> 900         if (result)
> >> 901                 goto out_free_levels;
> >> 902
> >> 903         br->flags._BQC_use_index = (level == max_level ? 0 : 1);
> >> 904
> >> 905         if (!br->flags._BQC_use_index) {
> >> 912                 for (i = 2; i < br->count; i++)
> >> 913                         if (level_old == br->levels[i])
> >> 914                                 level = level_old;
> >> 915                 goto set_level;
> >> 916         }
> >> why after level == max_level, it will still need set_level again?
> >> is this a bug, or it is necessary.
> >>
> > Because setting the backlight to max_level is just to check if _BQC uses
> > indexed value. We need to set the backlight back after this is done.
> >
> > thanks,
> > rui
> 
> Hi~
> 
> I'm wondering why check (level == max_level) can make sure if _BQC
> uses indexed value?
> Is it possible that both level and max_level is indexed value?
> 
If both _BQC and _BCL uses indexed value, then we don't need to treat
them as indexed value. :p

for example,
_BCL returns {0, 1, 2, 3, 4, 5, ... },  the index of level n is n.
If _BQC uses indexed value, it should returns n for level n.
so this equals a BIOS that both _BCL and _BQC use percentage values.

thanks,
rui

> Thank you very much.
>