[Mesa-dev] [PATCH] i965/miptree: Initialize mcs buffer only until clear color

[Pohjolainen, Topi]

On Fri, Apr 06, 2018 at 08:53:39AM -0700, Jason Ekstrand wrote:
> On Fri, Apr 6, 2018 at 8:22 AM, Rafael Antognolli <
> rafael.antognolli at intel.com> wrote:
> 
> > On Fri, Apr 06, 2018 at 06:07:52PM +0300, Topi Pohjolainen wrote:
> > > Otherwise even the clear color gets initialised to 0xFF. This
> > > allows enabling of color fast clears on ICL without regressing
> > > multisampling tests.
> > >
> > > CC: Rafael Antognolli <rafael.antognolli at intel.com>
> > > CC: Jason Ekstrand <jason at jlekstrand.net>
> > > CC: Nanley Chery <nanley.g.chery at intel.com>
> > > Signed-off-by: Topi Pohjolainen <topi.pohjolainen at intel.com>
> > > ---
> > >  src/mesa/drivers/dri/i965/intel_mipmap_tree.c | 7 ++++++-
> > >  1 file changed, 6 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/src/mesa/drivers/dri/i965/intel_mipmap_tree.c
> > b/src/mesa/drivers/dri/i965/intel_mipmap_tree.c
> > > index 89074a6..25f901d 100644
> > > --- a/src/mesa/drivers/dri/i965/intel_mipmap_tree.c
> > > +++ b/src/mesa/drivers/dri/i965/intel_mipmap_tree.c
> > > @@ -1680,7 +1680,12 @@ intel_miptree_init_mcs(struct brw_context *brw,
> > >        return;
> > >     }
> > >     void *data = map;
> > > -   memset(data, init_value, mt->mcs_buf->size);
> > > +
> > > +   /* Only initialize until clear color (if present). */
> > > +   const unsigned aux_size = mt->mcs_buf->clear_color_offset ?
> > > +                                mt->mcs_buf->clear_color_offset :
> > > +                                mt->mcs_buf->size;
> > > +   memset(data, init_value, aux_size);
> >
> 
> Why not just use mt->mcs_buf->aux_surf.size?
> 
> Also, I think we probably want to memset the clear color to 0 in case we
> get a recycled BO with unknown garbage in the clear value.

Good thinking, both points.

> 
> 
> > Hmm... that's a good catch, and I think we definitely should not
> > overwrite the clear color here.
> >
> > However, the initial value of the clear color shouldn't matter, right? I
> > think there might still be a bug hidden somewhere...

I agree. I started to look into MCS in more detail - I don't think I fully
understand how the clear color works there.

> >
> > Regardless of that, this patch is
> >
> > Reviewed-by: Rafael Antognolli <rafael.antognolli at intel.com>
> >
> > >     brw_bo_unmap(mt->mcs_buf->bo);
> > >  }
> > >
> > > --
> > > 2.7.4
> > >
> >