[Intel-gfx] [PATCH] drm/i915: A better maximum brightness for users.

[Paulo Zanoni]

2015-11-09 8:17 GMT-02:00 Jani Nikula <jani.nikula at linux.intel.com>:
> On Mon, 09 Nov 2015, "Shih-Yuan Lee (FourDollars)" <sylee at canonical.com> wrote:
>> The PWM brightness level of Dell XPS 13 (2015) is from 10 to 937 however
>> the sysfs brightness level always starts from 0 so it is better to use
>> 927 as the sysfs maximum brightness level and it becomes easier to map
>> from the PWM brightness level to the sysfs brightness level.
>
> We've been thinking we should provide a fixed range to userspace
> instead. Say, 0-100.

While not clearly stated, this reply and the further ones sound like a
rejection to his patch.

I'm not really an expert on backlight, but his idea sounds simple and
an overall improvement to the codebase. I don't think it's fair to
block a simple one-line improvement based on the fact that we have an
idea (that may or may not be implemented) for a possibly better
implementation. Why not apply his patch (in case we conclude it
doesn't have any bugs), and then go for the 0-100 idea once someone
actually decides to implement it?

Besides, isn't there the possibility of having a panel that has a
0-9999 range where the change from 0 to 9990 is negligible, and only
9991-9999 matters, so when we scale to 0-100 it will become basically
a on/off switch? We all learned to never underestimate panel hardware.

>
> BR,
> Jani.
>
>
>
>
>>
>> Signed-off-by: Shih-Yuan Lee (FourDollars) <sylee at canonical.com>
>> ---
>>  drivers/gpu/drm/i915/intel_panel.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/i915/intel_panel.c b/drivers/gpu/drm/i915/intel_panel.c
>> index a24df35..697fd4d 100644
>> --- a/drivers/gpu/drm/i915/intel_panel.c
>> +++ b/drivers/gpu/drm/i915/intel_panel.c
>> @@ -1211,7 +1211,7 @@ static int intel_backlight_device_register(struct intel_connector *connector)
>>        * Note: Everything should work even if the backlight device max
>>        * presented to the userspace is arbitrarily chosen.
>>        */
>> -     props.max_brightness = panel->backlight.max;
>> +     props.max_brightness = panel->backlight.max - panel->backlight.min;
>>       props.brightness = scale_hw_to_user(connector,
>>                                           panel->backlight.level,
>>                                           props.max_brightness);
>
> --
> Jani Nikula, Intel Open Source Technology Center
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-- 
Paulo Zanoni