Re: [PATCH 11/13] drm/i915: Turn off pipe gamma when it's not needed.

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Thu, Jan 17, 2019 at 10:40:23AM -0800, Matt Roper wrote:
> On Fri, Jan 11, 2019 at 07:08:21PM +0200, Ville Syrjala wrote:
> > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > 
> > The pipe internal precision is higher than what we currently program to
> > the degamma/gamma LUTs. We can get a higher quality image by bypassing
> > the LUTs when they're not needed. Let's do that.
> > 
> > Each plane has its own control bit for this, so we have to update
> > all active planes. The way we've done this we don't actually have
> > to run through the whole .check_plane() thing. And we actually
> > do the .color_check() after .check_plane() so we couldn't even do
> > that without shuffling the code around.
> > 
> > Additionally on pre-skl we have to update the primary plane regardless
> > of whether it's active or not on account of the primayr plane gamma
> 
> s/primayr/primary/
> 
> > enable bit also affecting the pipe bottom color.
> > 
> > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > ---
> >  drivers/gpu/drm/i915/intel_color.c | 55 ++++++++++++++++++++++++++++--
> >  1 file changed, 53 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/intel_color.c b/drivers/gpu/drm/i915/intel_color.c
> > index 8d7ea902a34b..a8b7428a64bf 100644
> > --- a/drivers/gpu/drm/i915/intel_color.c
> > +++ b/drivers/gpu/drm/i915/intel_color.c
> > @@ -633,27 +633,78 @@ void intel_color_commit(const struct intel_crtc_state *crtc_state)
> >  	dev_priv->display.color_commit(crtc_state);
> >  }
> >  
> > +static bool need_plane_update(struct intel_plane *plane,
> > +			      const struct intel_crtc_state *crtc_state)
> > +{
> > +	struct drm_i915_private *dev_priv = to_i915(plane->base.dev);
> > +
> > +	/*
> > +	 * On pre-SKL the pipe gamma enable and pipe csc enable for
> > +	 * the pipe bottom color are configured via the primary plane.
> > +	 * We have to reconfigure that even if the plane is inactive.
> > +	 */
> > +	return crtc_state->active_planes & BIT(plane->id) ||
> > +		(INTEL_GEN(dev_priv) < 9 &&
> > +		 plane->id == PLANE_PRIMARY);
> > +}
> > +
> > +static int
> > +intel_color_add_affected_planes(struct intel_crtc_state *new_crtc_state)
> > +{
> > +	struct intel_crtc *crtc = to_intel_crtc(new_crtc_state->base.crtc);
> > +	struct drm_i915_private *dev_priv = to_i915(crtc->base.dev);
> > +	struct intel_atomic_state *state =
> > +		to_intel_atomic_state(new_crtc_state->base.state);
> > +	const struct intel_crtc_state *old_crtc_state =
> > +		intel_atomic_get_old_crtc_state(state, crtc);
> > +	struct intel_plane *plane;
> > +
> > +	if (new_crtc_state->gamma_enable == old_crtc_state->gamma_enable)
> > +		return 0;
> > +
> > +	for_each_intel_plane_on_crtc(&dev_priv->drm, crtc, plane) {
> > +		struct intel_plane_state *plane_state;
> > +
> > +		if (!need_plane_update(plane, new_crtc_state))
> > +			continue;
> > +
> > +		plane_state = intel_atomic_get_plane_state(state, plane);
> > +		if (IS_ERR(plane_state))
> > +			return PTR_ERR(plane_state);
> > +
> > +		new_crtc_state->update_planes |= BIT(plane->id);
> > +	}
> > +
> > +	return 0;
> > +}
> > +
> >  int intel_color_check(struct intel_crtc_state *crtc_state)
> >  {
> >  	struct drm_i915_private *dev_priv = to_i915(crtc_state->base.crtc->dev);
> >  	const struct drm_property_blob *gamma_lut = crtc_state->base.gamma_lut;
> >  	const struct drm_property_blob *degamma_lut = crtc_state->base.degamma_lut;
> >  	size_t gamma_length, degamma_length;
> > +	int ret;
> >  
> >  	degamma_length = INTEL_INFO(dev_priv)->color.degamma_lut_size;
> >  	gamma_length = INTEL_INFO(dev_priv)->color.gamma_lut_size;
> >  
> > -	crtc_state->gamma_enable = true;
> > +	crtc_state->gamma_enable = gamma_lut || degamma_lut;
> >  
> >  	if (INTEL_GEN(dev_priv) >= 9 ||
> >  	    IS_BROADWELL(dev_priv) || IS_HASWELL(dev_priv))
> >  		crtc_state->csc_enable = true;
> >  
> > +	ret = intel_color_add_affected_planes(crtc_state);
> > +	if (ret)
> > +		return ret;
> > +
> >  	/*
> >  	 * We also allow no degamma lut/ctm and a gamma lut at the legacy
> >  	 * size (256 entries).
> >  	 */
> > -	if (crtc_state_is_legacy_gamma(crtc_state)) {
> > +	if (!crtc_state->gamma_enable ||
> > +	    crtc_state_is_legacy_gamma(crtc_state)) {
> >  		crtc_state->gamma_mode = GAMMA_MODE_MODE_8BIT;
> 
> If none of our planes are actually using the gamma, what does switching
> back to 8bit mode do for us?

Hopefilly nothing. Just a matter of selecting something for
consistency.

> 
> Regardless,
> 
> Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
> 
> 
> >  		return 0;
> >  	}
> > -- 
> > 2.19.2
> > 
> 
> -- 
> Matt Roper
> Graphics Software Engineer
> IoTG Platform Enabling & Development
> Intel Corporation
> (916) 356-2795

-- 
Ville Syrjälä
Intel
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