[Intel-gfx] [PATCH] drm/i915: expose a fixed brightness range to userspace

[Eoff, Ullysses A]

> -----Original Message-----
> From: Intel-gfx [mailto:intel-gfx-bounces at lists.freedesktop.org] On Behalf Of Eoff, Ullysses A
> Sent: Tuesday, November 18, 2014 3:19 PM
> To: Jani Nikula; Jesse Barnes
> Cc: stephane.marchesin at gmail.com; intel-gfx at lists.freedesktop.org
> Subject: Re: [Intel-gfx] [PATCH] drm/i915: expose a fixed brightness range to userspace
> 
> Thanks Jesse for the ack.
> 
> Unfortunately I just learned from Stéphane that there
> are certain devices which only support 256 levels, so this
> patch would do us no good at solving the real issue for
> such devices.
> 
> Why can't we just use a dynamic 1:1 mapping as was
> suggested before?  I would vote for that instead.
> 
> ----
> U. Artie

In all fairness, I guess Jesse did elude to the fact that there
would be such devices in the previous thread:

<http://lists.freedesktop.org/archives/intel-gfx/2014-November/055221.html>

I don't see why we shouldn't just expose the full 1:1 range to
userspace.   And let userspace decide what level stepping
makes sense for providing smooth backlight level transitions
to the end-user if necessary.

--U. Artie

> 
> > -----Original Message-----
> > From: Jesse Barnes [mailto:jbarnes at virtuousgeek.org]
> > Sent: Tuesday, November 18, 2014 9:23 AM
> > To: Eoff, Ullysses A
> > Cc: intel-gfx at lists.freedesktop.org; Jani Nikula
> > Subject: Re: [Intel-gfx] [PATCH] drm/i915: expose a fixed brightness range to userspace
> >
> > On Tue, 11 Nov 2014 12:30:38 -0800
> > "U. Artie Eoff" <ullysses.a.eoff at intel.com> wrote:
> >
> > > A userspace brightness range that is larger than the hardware
> > > brightness range does not have a 1:1 mapping and can result
> > > in brightness != actual_brightness for some values.
> > >
> > > Expose a fixed brightness range of [0..1000] to userspace so
> > > that all values can map 1:1 into the hardware brightness
> > > range.  This would assume that the hardware range is always
> > > greater than 1000, otherwise we're right back to the original
> > > issue.
> > >
> > > This patch is based on Jani Nikula's proposed change in the
> > > referenced ML thread, except use the range [0..1000] instead;
> > > which was recommended by Jesse Barnes for smoother backlight
> > > transitions.
> > >
> > > Reference: http://lists.freedesktop.org/archives/intel-gfx/2014-November/055221.html
> > > Signed-off-by: U. Artie Eoff <ullysses.a.eoff 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 4d63839..f74f5f2 100644
> > > --- a/drivers/gpu/drm/i915/intel_panel.c
> > > +++ b/drivers/gpu/drm/i915/intel_panel.c
> > > @@ -1057,7 +1057,7 @@ 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 = 1000;
> > >  	props.brightness = scale_hw_to_user(connector,
> > >  					    panel->backlight.level,
> > >  					    props.max_brightness);
> >
> > Yeah looks ok to me.  I guess Jani has to ack it too.
> >
> > Reviewed-by: Jesse Barnes <jbarnes at virtuousgeek.org>
> >
> > --
> > Jesse Barnes, Intel Open Source Technology Center
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