Re: [PATCH 4/9] drm/i915: add post-flush store dw workaround

[Daniel Vetter <daniel@ffwll.ch>]

On Wed, Sep 19, 2012 at 01:28:58PM -0700, Jesse Barnes wrote:
> Several platforms need this to flush the CS write buffers.

Chris spent quite some effort to dump less crap into the rings on gen6,
and your description here sounds like we only need this when flushing
write caches. Or it might only apply to CS writes (in which case this is
at the wrong spot). In any case, can you please double check where exactly
we need this and only add it there, with a neat comment explaining things
added?

I'm bitching because afair the CS stuff the windows driver emits (of which
I've seen some traces) only emits one such 8x MI_WRITE block per batch,
whereas your code here would emit 2 such 2x MI_WRITE blocks.

Thanks, Daniel
> 
> References: https://bugs.freedesktop.org/show_bug.cgi?id=50241
> Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
> ---
>  drivers/gpu/drm/i915/intel_ringbuffer.c |   15 ++++++++++++++-
>  1 file changed, 14 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
> index 55cdb4d..ef5101f 100644
> --- a/drivers/gpu/drm/i915/intel_ringbuffer.c
> +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
> @@ -216,7 +216,7 @@ gen6_render_ring_flush(struct intel_ring_buffer *ring,
>  	u32 flags = 0;
>  	struct pipe_control *pc = ring->private;
>  	u32 scratch_addr = pc->gtt_offset + 128;
> -	int ret;
> +	int ret, i;
>  
>  	/* Force SNB workarounds for PIPE_CONTROL flushes */
>  	ret = intel_emit_post_sync_nonzero_flush(ring);
> @@ -259,6 +259,19 @@ gen6_render_ring_flush(struct intel_ring_buffer *ring,
>  	intel_ring_emit(ring, 0);
>  	intel_ring_advance(ring);
>  
> +	ret = intel_ring_begin(ring, 4 * 8);
> +	if (ret)
> +		return ret;
> +
> +	for (i = 0; i < 8; i++) {
> +		intel_ring_emit(ring, MI_STORE_DWORD_INDEX);
> +		intel_ring_emit(ring, I915_GEM_SCRATCH_INDEX << MI_STORE_DWORD_INDEX_SHIFT);
> +		intel_ring_emit(ring, 0);
> +		intel_ring_emit(ring, MI_NOOP);
> +	}
> +	intel_ring_advance(ring);
> +
> +
>  	return 0;
>  }
>  
> -- 
> 1.7.9.5
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch