Question about ACPI Video

Question about ACPI Video

[luke lin]

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.

thx
luke
--
To unsubscribe from this list: send the line "unsubscribe linux-acpi" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: Question about ACPI Video

[Zhang Rui]

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


> thx
> luke
> --
> To unsubscribe from this list: send the line "unsubscribe linux-acpi" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: Question about ACPI Video

[Len Brown]

> > 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.

perhaps a good place for a comment?

thanks,
Len Brown, Intel Open Source Technology Center

Re: Question about ACPI Video

[Edward Shao]

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?

Thank you very much.

-- 
Best Regards,
Edward
--
To unsubscribe from this list: send the line "unsubscribe linux-acpi" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: Question about ACPI Video

[Zhang Rui]

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.
>