Re: [Intel-gfx] [PATCH 2/2] drm/i915: Stop adding planes to the commit needlessly

["Lisovskiy, Stanislav" <stanislav.lisovskiy@intel.com>]

On Thu, Mar 25, 2021 at 01:37:31PM +0200, Ville Syrjälä wrote:
> On Thu, Mar 25, 2021 at 11:35:53AM +0200, Lisovskiy, Stanislav wrote:
> > On Thu, Mar 25, 2021 at 02:44:15AM +0200, Ville Syrjala wrote:
> > > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > > 
> > > The dbuf bandwidth calculations don't need the planes to be
> > > added to the state. Each plane's data rate has already been
> > > precalculated and stored in the crtc state, and that with
> > > the dbuf slice usage for each plane is all the dbuf bandwidth
> > > code needs to figure out what the minimum cdclk is.
> > > 
> > > What we're trying to do here is make sure each plane recalculates
> > > its minimum cdclk (ie. plane->min_cdclk()) on those platforms where
> > > the number of active planes affects the result of said calculation.
> > > Nothing to do with any dbuf cdclk requirements.
> > 
> > So does it mean that if we lets say had active plane mask as
> > 011(planes 0, 1 were active) and new active planes are 101(planes 0, 2
> > are active) - we should not add plane 2 to the state?
> > Because hamming weight will be obviously same, however I think it would
> > be wrong not have plane 2 in the state at all then..
> > 
> > Or will it be added somewhere else?
> 
> If someone is asking to disable plane 2 then it will be added to
> the state already during the atomic/setplance ioctl handling.

Ok, I thought intel_atomic_check_planes function is intended for checking
which planes had changed and need to be added to the state.
It is a bit non-obvious as we are adding them only when their amount changes,
but not themself.

Reviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>

> 
> > 
> > 
> > Stan
> > 
> > > 
> > > Not sure if we had stuff in slightly different order or what,
> > > but at least in the current scheme this is not necessary.
> > > 
> > > Cc: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
> > > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > > ---
> > >  drivers/gpu/drm/i915/display/intel_display.c | 10 ++--------
> > >  1 file changed, 2 insertions(+), 8 deletions(-)
> > > 
> > > diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
> > > index 17490d29dc13..2300d58ba47f 100644
> > > --- a/drivers/gpu/drm/i915/display/intel_display.c
> > > +++ b/drivers/gpu/drm/i915/display/intel_display.c
> > > @@ -9811,7 +9811,7 @@ static bool active_planes_affects_min_cdclk(struct drm_i915_private *dev_priv)
> > >  	/* See {hsw,vlv,ivb}_plane_ratio() */
> > >  	return IS_BROADWELL(dev_priv) || IS_HASWELL(dev_priv) ||
> > >  		IS_CHERRYVIEW(dev_priv) || IS_VALLEYVIEW(dev_priv) ||
> > > -		IS_IVYBRIDGE(dev_priv) || (DISPLAY_VER(dev_priv) >= 11);
> > > +		IS_IVYBRIDGE(dev_priv);
> > >  }
> > >  
> > >  static int intel_crtc_add_bigjoiner_planes(struct intel_atomic_state *state,
> > > @@ -9898,13 +9898,7 @@ static int intel_atomic_check_planes(struct intel_atomic_state *state)
> > >  		old_active_planes = old_crtc_state->active_planes & ~BIT(PLANE_CURSOR);
> > >  		new_active_planes = new_crtc_state->active_planes & ~BIT(PLANE_CURSOR);
> > >  
> > > -		/*
> > > -		 * Not only the number of planes, but if the plane configuration had
> > > -		 * changed might already mean we need to recompute min CDCLK,
> > > -		 * because different planes might consume different amount of Dbuf bandwidth
> > > -		 * according to formula: Bw per plane = Pixel rate * bpp * pipe/plane scale factor
> > > -		 */
> > > -		if (old_active_planes == new_active_planes)
> > > +		if (hweight8(old_active_planes) == hweight8(new_active_planes))
> > >  			continue;
> > >  
> > >  		ret = intel_crtc_add_planes_to_state(state, crtc, new_active_planes);
> > > -- 
> > > 2.26.2
> > > 
> 
> -- 
> Ville Syrjälä
> Intel
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