[7/7] drm/i915/dp: Limit brightness level to vbt min brightness

[Kandpal, Suraj]

> -----Original Message-----
> From: Sebastian Wick <sebastian.wick at redhat.com>
> Sent: Friday, April 5, 2024 11:26 PM
> To: Kandpal, Suraj <suraj.kandpal at intel.com>
> Cc: intel-gfx at lists.freedesktop.org; Borah, Chaitanya Kumar
> <chaitanya.kumar.borah at intel.com>; Shankar, Uma
> <uma.shankar at intel.com>; Nautiyal, Ankit K <ankit.k.nautiyal at intel.com>;
> Murthy, Arun R <arun.r.murthy at intel.com>; Nikula, Jani
> <jani.nikula at intel.com>; Kumar, Naveen1 <naveen1.kumar at intel.com>
> Subject: Re: [7/7] drm/i915/dp: Limit brightness level to vbt min brightness
> 
> On Fri, Apr 05, 2024 at 02:07:05PM +0530, Suraj Kandpal wrote:
> > Limit minimum brightness to vbt min brightness when using aux based
> > brightness control to avoid letting the screen from going completely
> > blank.
> > Sometimes vbt can have some bogus values hence clamping the value for
> > sanity in case of corner case.
> 
> So, you're completely ignoring the value from the EDID now instead?
> 
> >

Also after having  deeper look using the vbt value directly still will not get the job done
Since that too can end up being 0.
Usually when using the pwm path when we set brightness to 0 it usually results in a
25 percent brightness which is what ill be doing  in the next revision.
Set the min_luminance as max(25% of max_luminance, min_luminance) that way
We don't ignore values.

Regards,
Suraj Kandpal
> > --v2
> > -Use something same mechanism to limit minimum brightness that PWM
> > method uses [Jani]
> >
> > Signed-off-by: Suraj Kandpal <suraj.kandpal at intel.com>
> > ---
> >  drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c | 10 +++++-----
> >  1 file changed, 5 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> > b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> > index 20dd5a6a0f3f..eb2a7225dfaa 100644
> > --- a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> > +++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> > @@ -411,6 +411,8 @@ intel_dp_aux_hdr_setup_backlight(struct
> intel_connector *connector, enum pipe pi
> >  	struct intel_panel *panel = &connector->panel;
> >  	struct drm_luminance_range_info *luminance_range =
> >  		&connector->base.display_info.luminance_range;
> > +	u32 min_level = clamp_t(u32,
> > +				connector-
> >panel.vbt.backlight.min_brightness, 0, 64);
> >  	int ret;
> >
> >  	drm_dbg_kms(&i915->drm, "[CONNECTOR:%d:%s] SDR backlight is
> > controlled through %s\n", @@ -427,14 +429,12 @@
> intel_dp_aux_hdr_setup_backlight(struct intel_connector *connector, enum
> pipe pi
> >  		}
> >  	}
> >
> > -	if (luminance_range->max_luminance) {
> > +	if (luminance_range->max_luminance)
> >  		panel->backlight.max = luminance_range->max_luminance;
> > -		panel->backlight.min = luminance_range->min_luminance;
> > -	} else {
> > +	else
> >  		panel->backlight.max = 512;
> > -		panel->backlight.min = 0;
> > -	}
> >
> > +	panel->backlight.min = min_level;
> >  	intel_dp_aux_write_panel_luminance_override(connector);
> >
> >  	drm_dbg_kms(&i915->drm, "[CONNECTOR:%d:%s] Using AUX HDR
> interface
> > for backlight control (range %d..%d)\n",