Re: [CI 18/25] drm/i915: Replace the pinned context address with its unique ID

[Dave Gordon <david.s.gordon@intel.com>]

On 28/04/16 09:56, Chris Wilson wrote:
> Rather than reuse the current location of the context in the global GTT
> for its hardware identifier, use the context's unique ID assigned to it
> for its whole lifetime.
>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> ---
>   drivers/gpu/drm/i915/i915_debugfs.c | 12 +++++-------
>   drivers/gpu/drm/i915/intel_lrc.c    | 39 +++++++++----------------------------
>   drivers/gpu/drm/i915/intel_lrc.h    |  3 ---
>   3 files changed, 14 insertions(+), 40 deletions(-)

[snip]

> @@ -315,14 +316,14 @@ static void
>   intel_lr_context_descriptor_update(struct intel_context *ctx,
>   				   struct intel_engine_cs *engine)
>   {
> -	uint64_t lrca, desc;
> +	u64 desc;
>
> -	lrca = ctx->engine[engine->id].lrc_vma->node.start +
> -	       LRC_PPHWSP_PN * PAGE_SIZE;
> +	BUILD_BUG_ON(MAX_CONTEXT_HW_ID > (1<<GEN8_CTX_ID_WIDTH));
>
> -	desc = engine->ctx_desc_template;		   /* bits  0-11 */
> -	desc |= lrca;					   /* bits 12-31 */
> -	desc |= (lrca >> PAGE_SHIFT) << GEN8_CTX_ID_SHIFT; /* bits 32-52 */
> +	desc = engine->ctx_desc_template;			/* bits  0-11 */
> +	desc |= ctx->engine[engine->id].lrc_vma->node.start +	/* bits 12-31 */
> +	       LRC_PPHWSP_PN * PAGE_SIZE;
> +	desc |= (u64)ctx->hw_id << GEN8_CTX_ID_SHIFT;		/* bits 32-52 */

I'd prefer to see the LRCA mentioned and explicitly computed in a local 
variable first, rather than hide the calculation in the middle of 
assembling the descriptor! In other words, as it was before -- the only 
line of this function that needed changing was the last one above.

.Dave.
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