[Intel-gfx] [RFC 03/39] drm/i915: Explicit power enable during deferred context initialisation

[Daniel Vetter]

On Fri, Jul 17, 2015 at 03:33:12PM +0100, John.C.Harrison at Intel.com wrote:
> From: John Harrison <John.C.Harrison at Intel.com>
> 
> A later patch in this series re-organises the batch buffer submission
> code. Part of that is to reduce the scope of a pm_get/put pair.
> Specifically, they previously wrapped the entire submission path from
> the very start to the very end, now they only wrap the actual hardware
> submission part in the back half.
> 
> While that is a good thing in general, it causes a problem with the
> deferred context initialisation. That is done quite early on in the
> execbuf code path - it happens at context validation time rather than
> context switch time. Some of the deferred work requires the power to
> be enabled. Hence this patch adds an explicit power reference count to
> the deferred initialisation code itself.

The main reason for grabbing rpm for the entire execbuf is writing ptes
for global gtt. This happens on gen6 due to some hilarious tlb aliasing hw
bug where we have to bind objects into both ggtt and ppgtt.
-Daniel

> 
> Change-Id: Id7b1535dfd8809a2bd5546272de2bbec39da2868
> Issue: GMINL-5159
> Signed-off-by: John Harrison <John.C.Harrison at Intel.com>
> ---
>  drivers/gpu/drm/i915/intel_lrc.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
> index 18dbd5c..8aa9a18 100644
> --- a/drivers/gpu/drm/i915/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/intel_lrc.c
> @@ -2317,12 +2317,15 @@ int intel_lr_context_deferred_create(struct intel_context *ctx,
>  	WARN_ON(ctx->legacy_hw_ctx.rcs_state != NULL);
>  	WARN_ON(ctx->engine[ring->id].state);
>  
> +	intel_runtime_pm_get(dev->dev_private);
> +
>  	context_size = round_up(get_lr_context_size(ring), 4096);
>  
>  	ctx_obj = i915_gem_alloc_object(dev, context_size);
>  	if (!ctx_obj) {
>  		DRM_DEBUG_DRIVER("Alloc LRC backing obj failed.\n");
> -		return -ENOMEM;
> +		ret = -ENOMEM;
> +		goto error_pm;
>  	}
>  
>  	if (is_global_default_ctx) {
> @@ -2331,7 +2334,7 @@ int intel_lr_context_deferred_create(struct intel_context *ctx,
>  			DRM_DEBUG_DRIVER("Pin LRC backing obj failed: %d\n",
>  					ret);
>  			drm_gem_object_unreference(&ctx_obj->base);
> -			return ret;
> +			goto error_pm;
>  		}
>  	}
>  
> @@ -2415,6 +2418,7 @@ int intel_lr_context_deferred_create(struct intel_context *ctx,
>  		ctx->rcs_initialized = true;
>  	}
>  
> +	intel_runtime_pm_put(dev->dev_private);
>  	return 0;
>  
>  error:
> @@ -2428,6 +2432,8 @@ error_unpin_ctx:
>  	if (is_global_default_ctx)
>  		i915_gem_object_ggtt_unpin(ctx_obj);
>  	drm_gem_object_unreference(&ctx_obj->base);
> +error_pm:
> +	intel_runtime_pm_put(dev->dev_private);
>  	return ret;
>  }
>  
> -- 
> 1.9.1
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch