Re: [PATCH 1/5] drm/i915: Disable compression tricks on JSL

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

On Fri, Jun 28, 2024 at 12:33:12AM +0200, Andi Shyti wrote:
> Hi Ville,
> 
> On Mon, Jun 24, 2024 at 06:05:34PM +0300, Ville Syrjala wrote:
> > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > 
> > Bspec asks us to disable some compression trick on JSL. While the
> > bspec description is pretty vague it looks like this is some extra
> > trick for 10bpc+ CCS which presumably the ICL derived display engine
> > doesn't support.
> > 
> > Note that we aren't currently exposing 10bpc CCS scanout support,
> > but once that gets added this presumably becomes an issue.
> > 
> > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > ---
> >  drivers/gpu/drm/i915/gt/intel_gt_regs.h     | 1 +
> >  drivers/gpu/drm/i915/gt/intel_workarounds.c | 9 +++++++++
> >  2 files changed, 10 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/i915/gt/intel_gt_regs.h b/drivers/gpu/drm/i915/gt/intel_gt_regs.h
> > index e42b3a5d4e63..af53c40e6c21 100644
> > --- a/drivers/gpu/drm/i915/gt/intel_gt_regs.h
> > +++ b/drivers/gpu/drm/i915/gt/intel_gt_regs.h
> > @@ -432,6 +432,7 @@
> >  #define XEHPG_INSTDONE_GEOM_SVG			MCR_REG(0x666c)
> >  
> >  #define CACHE_MODE_0_GEN7			_MMIO(0x7000) /* IVB+ */
> > +#define   DISABLE_REPACKING_FOR_COMPRESSION	REG_BIT(15) /* jsl+ */
> 
> I know that REG_BIT() is the correct one, but for conformity I
> would still use (1 << 15), otherwise we would have a mess of
> styles.

The file is full of both. I guess I could throw in a patch to
finish the conversion...

> 
> Besides, you are breaking the order here.

The order here is wrong for whatever reason. I suppose I
can cook up a patch to fix that too.

> 
> >  #define   RC_OP_FLUSH_ENABLE			(1 << 0)
> >  #define   HIZ_RAW_STALL_OPT_DISABLE		(1 << 2)
> >  #define CACHE_MODE_1				_MMIO(0x7004) /* IVB+ */
> > diff --git a/drivers/gpu/drm/i915/gt/intel_workarounds.c b/drivers/gpu/drm/i915/gt/intel_workarounds.c
> > index 09a287c1aedd..a424b442493f 100644
> > --- a/drivers/gpu/drm/i915/gt/intel_workarounds.c
> > +++ b/drivers/gpu/drm/i915/gt/intel_workarounds.c
> > @@ -2286,6 +2286,15 @@ rcs_engine_wa_init(struct intel_engine_cs *engine, struct i915_wa_list *wal)
> >  			     GEN8_RC_SEMA_IDLE_MSG_DISABLE);
> >  	}
> >  
> > +	if (IS_JASPERLAKE(i915) || IS_ELKHARTLAKE(i915)) {
> > +		/*
> > +		 * "Disable Repacking for Compression (masked R/W access)
> > +		 *  before rendering compressed surfaces for display."
> > +		 */
> > +		wa_masked_en(wal, CACHE_MODE_0_GEN7,
> > +			     DISABLE_REPACKING_FOR_COMPRESSION);
> 
> It is vague, indeed, but the description says that repacking
> provides a boost in performance and "improvement in Lossless
> Compression Algo" (whatever that means, I'm sailing in unknown
> waters here :-) )
> 
> How did you get here?

Bspec:18437 and then I read through the linked HSDs.

-- 
Ville Syrjälä
Intel