Re: [Intel-gfx] [PATCH 2/4] drm/i915: Don't check for wm changes until we've compute the wms fully

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

On Wed, Mar 04, 2020 at 12:21:01AM +0000, Souza, Jose wrote:
> On Fri, 2020-02-28 at 22:35 +0200, Ville Syrjala wrote:
> > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > 
> > Currently we're comparing the watermarks between the old and new
> > states
> > before we've fully computed the new watermarks. In particular
> > skl_build_pipe_wm() will not account for the amount of ddb space
> > we'll
> > have. That information is only available during skl_compute_ddb()
> > which will proceed to zero out any watermark level exceeding the
> > ddb allocation. If we're short on ddb space this will end up
> > adding the plane to the state due erronously determining that the
> > watermarks have changed. Fix the problem by deferring
> > skl_wm_add_affected_planes() until we have the final watermarks
> > computed.
> > 
> > Noticed this when trying enable transition watermarks on glk.
> > We now computed the trans_wm as 28, but we only had 14 blocks
> > of ddb, and thus skl_compute_ddb() ended up disabling the cursor
> > trans_wm every time. Thus we ended up adding the cursor to every
> > commit that didn't actually affect the cursor at all.
> > 
> > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > ---
> >  drivers/gpu/drm/i915/intel_pm.c | 16 ++++++++++++----
> >  1 file changed, 12 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/intel_pm.c
> > b/drivers/gpu/drm/i915/intel_pm.c
> > index 39299811b650..a3d76e69caae 100644
> > --- a/drivers/gpu/drm/i915/intel_pm.c
> > +++ b/drivers/gpu/drm/i915/intel_pm.c
> > @@ -5762,16 +5762,24 @@ skl_compute_wm(struct intel_atomic_state
> > *state)
> >  		ret = skl_build_pipe_wm(new_crtc_state);
> >  		if (ret)
> >  			return ret;
> > -
> > -		ret = skl_wm_add_affected_planes(state, crtc);
> > -		if (ret)
> > -			return ret;
> >  	}
> >  
> >  	ret = skl_compute_ddb(state);
> >  	if (ret)
> >  		return ret;
> >  
> > +	/*
> > +	 * skl_compute_ddb() will have adjusted the final watermarks
> > +	 * based on how much ddb is available. Now we can actually
> > +	 * check if the final watermarks changed.
> > +	 */
> > +	for_each_oldnew_intel_crtc_in_state(state, crtc,
> > old_crtc_state,
> > +					    new_crtc_state, i) {
> > +		ret = skl_wm_add_affected_planes(state, crtc);
> > +		if (ret)
> > +			return ret;
> > +	}
> 
> skl_compute_ddb() is already calling skl_wm_add_affected_planes() after
> do the ddb allocation for each pipe, so we could remove this chunk,

skl_compute_ddb() calls skl_*ddb*_add_affected_planes(), which is a
different thing.

> with that:
> 
> Reviewed-by: José Roberto de Souza <jose.souza@intel.com>
> 
> > +
> >  	skl_print_wm_changes(state);
> >  
> >  	return 0;

-- 
Ville Syrjälä
Intel
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