[Intel-gfx] [PATCH 2/6] drm/i915/vlv: Added a rendering specific Hw WA 'WaReadAfterWriteHazard'

[Ville Syrjälä]

On Wed, Jan 22, 2014 at 09:15:06AM +0530, akash.goel at intel.com wrote:
> From: Akash Goel <akash.goel at intel.com>
> 
> Added a new rendering specific Workaround 'WaReadAfterWriteHazard'.
> In this WA, need to add 12 MI Store Dword commands to ensure proper
> flush of h/w pipeline.
> 
> Signed-off-by: Akash Goel <akash.goel at intel.com>
> ---
>  drivers/gpu/drm/i915/intel_ringbuffer.c | 25 +++++++++++++++++++++++++
>  1 file changed, 25 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
> index 133d273..e8ec536 100644
> --- a/drivers/gpu/drm/i915/intel_ringbuffer.c
> +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
> @@ -2167,6 +2167,31 @@ intel_ring_flush_all_caches(struct intel_ring_buffer *ring)
>  
>  	trace_i915_gem_ring_flush(ring, 0, I915_GEM_GPU_DOMAINS);
>  
> +	if (IS_VALLEYVIEW(ring->dev)) {
> +		/*
> +		 * WaReadAfterWriteHazard
> +		 * Send a number of Store Data commands here to finish
> +		 * flushing hardware pipeline.This is needed in the case
> +		 * where the next workload tries reading from the same
> +		 * surface that this batch writes to. Without these StoreDWs,
> +		 * not all of the data will actually be flushd to the surface
> +		 * by the time the next batch starts reading it, possibly
> +		 * causing a small amount of corruption.
> +		 */
> +		int i;
> +		ret = intel_ring_begin(ring, 4 * 12);

BSpec says 8 is enough. Is Bspec incorrect.

Also this workaround is also listed for everything SNB+.

> +		if (ret)
> +			return ret;
> +		for (i = 0; i < 12; i++) {
> +			intel_ring_emit(ring, MI_STORE_DWORD_INDEX);
> +			intel_ring_emit(ring, I915_GEM_HWS_SCRATCH_INDEX <<
> +							MI_STORE_DWORD_INDEX_SHIFT);
> +			intel_ring_emit(ring, 0);
> +			intel_ring_emit(ring, MI_NOOP);
> +		}
> +		intel_ring_advance(ring);
> +	}
> +
>  	ring->gpu_caches_dirty = false;
>  	return 0;
>  }
> -- 
> 1.8.5.2
> 
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-- 
Ville Syrjälä
Intel OTC