[Mesa-dev] [PATCH 3/4] i965/gen9: Don't use encrypted MOCS

[Ben Widawsky]

On Thu, Jun 18, 2015 at 03:41:50PM -0700, Kenneth Graunke wrote:
> On Wednesday, June 17, 2015 03:50:13 PM Ben Widawsky wrote:
> > On gen9+ MOCS is an index into a table. It is 7 bits, and AFAICT, bit 0 is for
> > doing encrypted reads.
> > 
> > I don't recall how I decided to do this for BXT. I don't know this patch was
> > ever needed, since it seems nothing is broken today on SKL. Furthermore, this
> > patch may no longer be needed because of the ongoing changes with MOCS setup. It
> > is what is being used/tested, so it's included in the series.
> > 
> > The chosen values are the old values left shifted. That was also an arbitrary
> > choice.
> > 
> > Cc:  Francisco Jerez <currojerez at riseup.net>
> > Signed-off-by: Ben Widawsky <ben at bwidawsk.net>
> > ---
> >  src/mesa/drivers/dri/i965/brw_defines.h | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/src/mesa/drivers/dri/i965/brw_defines.h b/src/mesa/drivers/dri/i965/brw_defines.h
> > index bfcc442..5358edc 100644
> > --- a/src/mesa/drivers/dri/i965/brw_defines.h
> > +++ b/src/mesa/drivers/dri/i965/brw_defines.h
> > @@ -2495,8 +2495,8 @@ enum brw_wm_barycentric_interp_mode {
> >   * cache settings.  We still use only either write-back or write-through; and
> >   * rely on the documented default values.
> >   */
> > -#define SKL_MOCS_WB 9
> > -#define SKL_MOCS_WT 5
> > +#define SKL_MOCS_WB 0x12
> > +#define SKL_MOCS_WT 0xa
> 
> 
> Yeah, it looks like Kristian made these defines the indices into the
> table, but may have missed that the MOCS field puts that table index in
> [6:1] and bit 0 is something else.
> 
> So shifting left by 1 seems like a good plan.  Perhaps write it as
> 
> #define SKL_MOCS_WB (0b000101 << 1)
> #define SKL_MOCS_WT (0b001001 << 1)
> 

You meant this, right (you reversed it, I think)?
#define SKL_MOCS_WB (0b001001 << 1)
#define SKL_MOCS_WT (0b000101 << 1)


> so the index value is written like it is in the documentation, and the
> shift 1 indicates moving it into the right place for MOCS?
> 
> Either way,
> Reviewed-by: Kenneth Graunke <kenneth at whitecape.org>
> 
> Incidentally...the WT value (index 5) appears to skip eLLC - the target
> cache is 01b = "LLC only".  That doesn't seem desirable.  We probably
> want index 6 instead (0b000110 << 1) which uses both LLC and eLLC.
> 
> That said, we shouldn't ever be using WT in the driver - we want to use
> the PTE value.  (krh even added a FINISHME comment to that effect.)
> 
> I think a proper value for that would be:
> #define SKL_MOCS_PTE (0b000010 << 1)
> (Default: 0b000010,
>  LeCC = 0x00 - use cacheability controls from page table / ...
>  TC = LLC/eLLC allowed)
> 
> We could either fix the _WT define or just delete it.
> 
> >  
> >  #define MEDIA_VFE_STATE                         0x7000
> >  /* GEN7 DW2, GEN8+ DW3 */
> > 

I'll get on this too. Thanks.