Re: [PATCH v2] drm/i915/execlists: Delay updating ring register state after resume

[Mika Kuoppala <mika.kuoppala@linux.intel.com>]

Chris Wilson <chris@chris-wilson.co.uk> writes:

> Now that we reload both RING_HEAD and RING_TAIL when rebinding the
> context, we do not need to scrub those registers immediately on resume.
>
> v2: Handle the perma-pinned contexts.
>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/intel_lrc.c | 31 ++++++++++++-------------------
>  1 file changed, 12 insertions(+), 19 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
> index 654634254b64..2bf5128efb26 100644
> --- a/drivers/gpu/drm/i915/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/intel_lrc.c
> @@ -2536,13 +2536,14 @@ static int execlists_context_deferred_alloc(struct i915_gem_context *ctx,
>  	return ret;
>  }
>  
> -void intel_lr_context_resume(struct drm_i915_private *dev_priv)
> +void intel_lr_context_resume(struct drm_i915_private *i915)
>  {
>  	struct intel_engine_cs *engine;
>  	struct i915_gem_context *ctx;
>  	enum intel_engine_id id;
>  
> -	/* Because we emit WA_TAIL_DWORDS there may be a disparity
> +	/*
> +	 * Because we emit WA_TAIL_DWORDS there may be a disparity
>  	 * between our bookkeeping in ce->ring->head and ce->ring->tail and
>  	 * that stored in context. As we only write new commands from
>  	 * ce->ring->tail onwards, everything before that is junk. If the GPU
> @@ -2552,27 +2553,19 @@ void intel_lr_context_resume(struct drm_i915_private *dev_priv)
>  	 * So to avoid that we reset the context images upon resume. For
>  	 * simplicity, we just zero everything out.
>  	 */
> -	list_for_each_entry(ctx, &dev_priv->contexts.list, link) {
> -		for_each_engine(engine, dev_priv, id) {
> -			struct intel_context *ce = &ctx->engine[engine->id];
> -			u32 *reg;
> -
> -			if (!ce->state)
> -				continue;
> +	list_for_each_entry(ctx, &i915->contexts.list, link) {
> +		for_each_engine(engine, i915, id) {
> +			struct intel_context *ce = &ctx->engine[id];
>  
> -			reg = i915_gem_object_pin_map(ce->state->obj,
> -						      I915_MAP_WB);
> -			if (WARN_ON(IS_ERR(reg)))
> +			if (!ce->ring)
>  				continue;
>  
> -			reg += LRC_STATE_PN * PAGE_SIZE / sizeof(*reg);
> -			reg[CTX_RING_HEAD+1] = 0;
> -			reg[CTX_RING_TAIL+1] = 0;
> -
> -			ce->state->obj->mm.dirty = true;
> -			i915_gem_object_unpin_map(ce->state->obj);
> -
>  			intel_ring_reset(ce->ring, 0);
> +
> +			if (ce->pin_count) { /* otherwise done in context_pin */

From my understanding this is for kernel context only. So the comment
should mention the kernel context.

Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>

> +				ce->lrc_reg_state[CTX_RING_HEAD+1] = 0;
> +				ce->lrc_reg_state[CTX_RING_TAIL+1] = 0;
> +			}
>  		}
>  	}
>  }
> -- 
> 2.16.3
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