Re: [PATCH] drm/i915: Tidy workaround batch buffer emission

[Chris Wilson <chris@chris-wilson.co.uk>]

On Wed, Feb 08, 2017 at 01:13:48PM +0000, Tvrtko Ursulin wrote:
> From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> -static int gen9_init_perctx_bb(struct intel_engine_cs *engine,
> -			       struct i915_wa_ctx_bb *wa_ctx,
> -			       uint32_t *batch,
> -			       uint32_t *offset)
> +static u32 *gen9_init_perctx_bb(struct intel_engine_cs *engine, u32 *batch)
>  {
> -	uint32_t index = wa_ctx_start(wa_ctx, *offset, CACHELINE_DWORDS);
> -
> -	wa_ctx_emit(batch, index, MI_BATCH_BUFFER_END);
> +	*batch++ = MI_BATCH_BUFFER_END;
>  
> -	return wa_ctx_end(wa_ctx, *offset = index, 1);
> +	return batch;
>  }

Transformation looks reasonable, but I'd like to omit this per-ctx bb
when empty.

> +	/*
> +	 * Emit the two workaround batch buffers, recording the offset from the
> +	 * start of the workaround batch buffer object for each and their
> +	 * respective sizes.
> +	 */
> +	for (i = 0; i < ARRAY_SIZE(wa_bb_f); i++) {
> +		wa_bb[i]->offset = ALIGN(batch_ptr - batch, CACHELINE_DWORDS);
> +		batch_ptr = wa_bb_f[i](engine, batch_ptr);
> +		wa_bb[i]->size = batch_ptr - &batch[wa_bb[i]->offset];

Which will break this pattern. At the least we could do

if (!ww_bb_fn[i])
	continue;

And then skip loading into the context image if size==0.

I'll double check the mechanical aspects in a bit.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre
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