[Mesa-dev] [PATCH] i965/skl/gt4: Fix URB programming restriction.

[Kenneth Graunke]

On Saturday, November 07, 2015 08:40:51 AM Ben Widawsky wrote:
> On Fri, Nov 06, 2015 at 07:29:18PM -0800, Kenneth Graunke wrote:
> > On Friday, November 06, 2015 06:12:27 PM Ben Widawsky wrote:
> > > The comment in the code details the restriction. Thanks to Ken for having a very
> > > helpful conversation with me, and spotting the blurb in the link I sent him :P.
> > > 
> > > There are still stability problems for me on GT4, but this definitely helps with
> > > some of the failures.
> > > 
> > > Cc: Kenneth Graunke <kenneth at whitecape.org>
> > > Cc: Jordan Justen <jordan.l.justen at intel.com>
> > > Cc: mesa-stable at lists.freedesktop.org (if the original gt4 patch goes to stable)
> > > ---
> > > 
> > > Sarah, you should check this on KBL.
> > > Cc: Sarah Sharp <sarah.a.sharp at linux.intel.com>
> > > ---
> > >  src/mesa/drivers/dri/i965/brw_device_info.c | 8 ++++++++
> > >  1 file changed, 8 insertions(+)
> > > 
> > > diff --git a/src/mesa/drivers/dri/i965/brw_device_info.c b/src/mesa/drivers/dri/i965/brw_device_info.c
> > > index 2ebc084..6117fd3 100644
> > > --- a/src/mesa/drivers/dri/i965/brw_device_info.c
> > > +++ b/src/mesa/drivers/dri/i965/brw_device_info.c
> > > @@ -337,6 +337,14 @@ static const struct brw_device_info brw_device_info_skl_gt3 = {
> > >  
> > >  static const struct brw_device_info brw_device_info_skl_gt4 = {
> > >     GEN9_FEATURES, .gt = 4,
> > > +   /* From the docs:
> > > +    *   URB is limited to 1008KB due to programming restrictions. This is not a
> > > +    *   restriction of the L3 implementation, but of the FF and other clients.
> > > +    *   Therefore, in a GT4 implementation it is possible for the programmed
> > > +    *   allocation of the L3 data array to provide 3*384KB=1152MB [sic] for URB,
> > > +    *   but only 1008KB of this will be used.
> > > +    */
> > 
> > We should at least say which page/section this comes from (the section
> > name exists in the Broadwell PRM, so it's not particularly secret).
> > 
> > Please put the text in quotes too.  My suggested formatting:
> > 
> >    /* From the "L3 Allocation and Programming" documentation:
> >     *
> >     * "URB is limited to 1008KB due to programming restrictions.  This
> >     *  is not a restriction of the L3 implementation, but of the FF and
> >     *  other clients.  Therefore, in a GT4 implementation it is
> >     *  possible for the programmed allocation of the L3 data array to
> >     *  provide 3*384KB=1152MB [sic] for URB, but only 1008KB of this
> >     *  will be used."
> >     */
> > 
> > Regardless,
> > Reviewed-by: Kenneth Graunke <kenneth at whitecape.org>
> > 
> 
> Thanks! I had no idea it was in the BDW PRMs.

You can change "1152MB [sic]" to "1152KB" as they've fixed the docs :)

--Ken
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