[Intel-gfx] [PATCH] drm/i915: Allow minimum brightness upon backlight enable

[Jani Nikula]

On Fri, 02 Oct 2015, Chris Wilson <chris at chris-wilson.co.uk> wrote:
> On Fri, Oct 02, 2015 at 10:50:50AM +0300, Jani Nikula wrote:
>> On Fri, 02 Oct 2015, clinton.a.taylor at intel.com wrote:
>> > From: Clint Taylor <clinton.a.taylor at intel.com>
>> >
>> > backlight minimum is a valid value so you don't need to set maximum.
>> >
>> > Signed-off-by: Clint Taylor <clinton.a.taylor at intel.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 4d28c7b..d509904 100644
>> > --- a/drivers/gpu/drm/i915/intel_panel.c
>> > +++ b/drivers/gpu/drm/i915/intel_panel.c
>> > @@ -1069,7 +1069,7 @@ void intel_panel_enable_backlight(struct intel_connector *connector)
>> >  
>> >  	WARN_ON(panel->backlight.max == 0);
>> >  
>> > -	if (panel->backlight.level <= panel->backlight.min) {
>> > +	if (panel->backlight.level < panel->backlight.min) {
>> >  		panel->backlight.level = panel->backlight.max;
>> >  		if (panel->backlight.device)
>> >  			panel->backlight.device->props.brightness =
>> 
>> This is policy in action in the kernel. We have this whole if block here
>> because some, uh, misguided userspace sets brightness to minimum before
>> switching the backlight off, and assumes enabling backlight cranks up
>> the brightness as well. (*)
>
> If you mean X, no. It has to set the backlight because on some intel
> models the backlight is not routed through i915 and so it needs to
> explicitly control it. On resume, it sets the previous value. This is
> just a broken kernel.

Okay, I guess I'm willing to give this a shot. This may result in
regression reports, but let's see.

However, the meaning of the whole check changes. What Clint now checks
(level below minimum) shouldn't happen, something failed already. Maybe
we should set the level to minimum instead, with debug logging?

BR,
Jani.

-- 
Jani Nikula, Intel Open Source Technology Center