Re: [PATCH] acpi: fix brightness level is initialized to zero when BIOS does not restore the brightness value to _BQC.

[joeyli <jlee@suse.com>]

於 一，2012-10-01 於 15:03 +0800，Alex Hung 提到：
> On 10/01/2012 02:47 PM, joeyli wrote:
> > Hi Alex,
> >
> > 於 一，2012-10-01 於 13:39 +0800，Alex Hung 提到：
> >> Signed-off-by: Alex Hung <alex.hung@canonical.com>
> >> ---
> >>   drivers/acpi/video.c |    4 ++++
> >>   1 files changed, 4 insertions(+), 0 deletions(-)
> >>
> >> diff --git a/drivers/acpi/video.c b/drivers/acpi/video.c
> >> index 42b226e..eaa9573 100644
> >> --- a/drivers/acpi/video.c
> >> +++ b/drivers/acpi/video.c
> >> @@ -724,6 +724,10 @@ acpi_video_init_brightness(struct acpi_video_device *device)
> >>   				if (level_old == br->levels[i])
> >>   					level = level_old;
> >>   		}
> >> +
> >> +		if (level == 0)
> >> +			level = br->levels[(br->count) / 2 + 1];
> >
> > Looks here used the 50% brightness level.
> >
> > Per comment in video.c, we want set the backlight to max_level when
> > level_old is invalid:
> >
> >          if (!br->flags._BQC_use_index) {
> >                  /*
> >                   * Set the backlight to the initial state.
> >                   * On some buggy laptops, _BQC returns an uninitialized value
> >                   * when invoked for the first time, i.e. level_old is invalid.
> >                   * set the backlight to max_level in this case
> >                   */
> >
> > I think here used max_level to fulfill it, e.g.
> > 	
> > +		if (level == 0)
> > +			level = max_level;
> >
> > How do you think?
> Hi Joey,
> 
> I was debating with myself which level to be set, ex. 50%, ~75% or 100%, 
> and I think 50% *might* be closer to normal use-case (just a personal 
> guess).
> 
> However, "max_level" seems to fit best if we treat the initial zero 
> brightness in invalid. I can modify it according it that's preferred.
> 
> Thanks for the feedback.
> 
> Cheers,
> Alex Hung
> 

hm.... I have a question for what's the BIOS's problem that causes
'level == 0'?
That implied the issue machine's max_level is 0?

		/*
		 * Set the level to maximum and check if _BQC uses indexed value
		 */
		result = acpi_video_device_lcd_set_level(device, max_level);		/* write max_level purposely, then read level back, compare them */
		...
		result = acpi_video_device_lcd_get_level_current(device, &level, 0);
		...
		br->flags._BQC_use_index = (level == max_level ? 0 : 1);
		if (!br->flags._BQC_use_index) {				/* _BQC_use_index is 0 will run into if, means level == max_level */

So, looks the 'level == max_level == 0' when level_old is invalid.

Just wonder what's defect of BIOS (in _BCL?) causes problem.


Thanks a lot!
Joey Lee


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