Re: [PATCH] [v2] drm/i915: Limit VF cache invalidate workaround usage to gen9

[Ben Widawsky <benjamin.widawsky@intel.com>]

On Thu, Dec 17, 2015 at 10:49:24PM +0200, Imre Deak wrote:
> On Thu, 2015-12-17 at 09:49 -0800, Ben Widawsky wrote:
> > It is unclear if this is even required on BXT.
> 
> I'm not sure either, I only added it on the premise that it was marked
> as SKL+ originally in BSpec. The revision log entry in BSpec has this
> much to say:
> """
> The workaround that requires an empty PIPE_CONTROL before a
> PIPE_CONTROL with a VF Cache Invalidation Enable is only for SKL and
> not SKL+. The bug was fixed in CNL with the following HSD:...
> """
> Which doesn't make this clear either imo.
> 
> > v2: Make sure to set the default value to false. Uncertain how my compiler
> > doesn't complain with v1.
> > 
> > Cc: Imre Deak <imre.deak@intel.com>
> > Signed-off-by: Ben Widawsky <benjamin.widawsky@intel.com>
> > ---
> >  drivers/gpu/drm/i915/intel_lrc.c | 16 ++++++++--------
> >  1 file changed, 8 insertions(+), 8 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
> > index 519cea32..af1e001 100644
> > --- a/drivers/gpu/drm/i915/intel_lrc.c
> > +++ b/drivers/gpu/drm/i915/intel_lrc.c
> > @@ -1695,7 +1695,7 @@ static int gen8_emit_flush_render(struct drm_i915_gem_request *request,
> >  	struct intel_ringbuffer *ringbuf = request->ringbuf;
> >  	struct intel_engine_cs *ring = ringbuf->ring;
> >  	u32 scratch_addr = ring->scratch.gtt_offset + 2 * CACHELINE_BYTES;
> > -	bool vf_flush_wa;
> > +	bool vf_flush_wa = false;
> >  	u32 flags = 0;
> >  	int ret;
> >  
> > @@ -1716,14 +1716,14 @@ static int gen8_emit_flush_render(struct drm_i915_gem_request *request,
> >  		flags |= PIPE_CONTROL_STATE_CACHE_INVALIDATE;
> >  		flags |= PIPE_CONTROL_QW_WRITE;
> >  		flags |= PIPE_CONTROL_GLOBAL_GTT_IVB;
> > -	}
> >  
> > -	/*
> > -	 * On GEN9+ Before VF_CACHE_INVALIDATE we need to emit a NULL pipe
> > -	 * control.
> > -	 */
> > -	vf_flush_wa = INTEL_INFO(ring->dev)->gen >= 9 &&
> > -		      flags & PIPE_CONTROL_VF_CACHE_INVALIDATE;
> > +		/*
> > +		 * On GEN9: before VF_CACHE_INVALIDATE we need to emit a NULL
> > +		 * pipe control.
> > +		 */
> > +> 		if (IS_GEN9(ring->dev))
> 
> Nitpick: INTEL_INFO()->gen == 9 is the preferred way. Either way:
> Reviewed-by: Imre Deak <imre.deak@intel.com>
> 

Sounds good to me. Does someone mind fixing this up when they push? This patch
is a pre-requisite to another internal patch I have at the moment.

> > +			vf_flush_wa = true;
> > +	}
> >  
> >  	ret = intel_logical_ring_begin(request, vf_flush_wa ? 12 : 6);
> >  	if (ret)

-- 
Ben Widawsky, Intel Open Source Technology Center
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