Re: [PATCH 1/2] drm/i915/gt: Disable HW load balancing for CCS

[Andi Shyti <andi.shyti@linux.intel.com>]

Hi Matt,

On Thu, Feb 15, 2024 at 08:55:41AM -0800, Matt Roper wrote:
> On Thu, Feb 15, 2024 at 02:59:23PM +0100, Andi Shyti wrote:
> > The hardware should not dynamically balance the load between CCS
> > engines. Wa_16016805146 recommends disabling it across all
> 
> Is this the right workaround number?  When I check the database, this
> workaround was rejected on both DG2-G10 and DG2-G11, and doesn't even
> have an entry for DG2-G12.
> 
> There are other workarounds that sound somewhat related to load
> balancing (e.g., part 3 of Wa_14019159160), but what's asked there is
> more involved than just setting one register bit and conflicts a bit
> with the second patch of this series.

thanks for checking it. Indeed the WA I mentioned is limited to
a specific platform. This recommendation comes in different WA,
e.g. this one: Wa_14019186972 (3rd point). Will start using that
as a reference.

Thank you.
Andi

> 
> 
> Matt
> 
> > platforms.
> > 
> > Fixes: d2eae8e98d59 ("drm/i915/dg2: Drop force_probe requirement")
> > Signed-off-by: Andi Shyti <andi.shyti@linux.intel.com>
> > Cc: Chris Wilson <chris.p.wilson@linux.intel.com>
> > Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> > Cc: Matt Roper <matthew.d.roper@intel.com>
> > Cc: <stable@vger.kernel.org> # v6.2+
> > ---
> >  drivers/gpu/drm/i915/gt/intel_gt_regs.h     | 1 +
> >  drivers/gpu/drm/i915/gt/intel_workarounds.c | 6 ++++++
> >  2 files changed, 7 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/i915/gt/intel_gt_regs.h b/drivers/gpu/drm/i915/gt/intel_gt_regs.h
> > index 50962cfd1353..cf709f6c05ae 100644
> > --- a/drivers/gpu/drm/i915/gt/intel_gt_regs.h
> > +++ b/drivers/gpu/drm/i915/gt/intel_gt_regs.h
> > @@ -1478,6 +1478,7 @@
> >  
> >  #define GEN12_RCU_MODE				_MMIO(0x14800)
> >  #define   GEN12_RCU_MODE_CCS_ENABLE		REG_BIT(0)
> > +#define   XEHP_RCU_MODE_FIXED_SLICE_CCS_MODE	REG_BIT(1)
> >  
> >  #define CHV_FUSE_GT				_MMIO(VLV_GUNIT_BASE + 0x2168)
> >  #define   CHV_FGT_DISABLE_SS0			(1 << 10)
> > diff --git a/drivers/gpu/drm/i915/gt/intel_workarounds.c b/drivers/gpu/drm/i915/gt/intel_workarounds.c
> > index d67d44611c28..7f42c8015f71 100644
> > --- a/drivers/gpu/drm/i915/gt/intel_workarounds.c
> > +++ b/drivers/gpu/drm/i915/gt/intel_workarounds.c
> > @@ -2988,6 +2988,12 @@ general_render_compute_wa_init(struct intel_engine_cs *engine, struct i915_wa_li
> >  		wa_mcr_masked_en(wal, GEN8_HALF_SLICE_CHICKEN1,
> >  				 GEN7_PSD_SINGLE_PORT_DISPATCH_ENABLE);
> >  	}
> > +
> > +	/*
> > +	 * Wa_16016805146: disable the CCS load balancing
> > +	 * indiscriminately for all the platforms
> > +	 */
> > +	wa_masked_en(wal, GEN12_RCU_MODE, XEHP_RCU_MODE_FIXED_SLICE_CCS_MODE);
> >  }
> >  
> >  static void
> > -- 
> > 2.43.0
> > 
> 
> -- 
> Matt Roper
> Graphics Software Engineer
> Linux GPU Platform Enablement
> Intel Corporation