Re: [PATCH 06/42] drm/i915: Support asynchronous waits on struct fence from i915_gem_request

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 07/10/2016 10:45, Chris Wilson wrote:
> We will need to wait on DMA completion (as signaled via struct fence)
> before executing our i915_gem_request. Therefore we want to expose a
> method for adding the await on the fence itself to the request.
>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>   drivers/gpu/drm/i915/i915_gem_request.c | 40 +++++++++++++++++++++++++++++++++
>   drivers/gpu/drm/i915/i915_gem_request.h |  2 ++
>   2 files changed, 42 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/i915_gem_request.c b/drivers/gpu/drm/i915/i915_gem_request.c
> index 8832f8ec1583..e1f7a32d4080 100644
> --- a/drivers/gpu/drm/i915/i915_gem_request.c
> +++ b/drivers/gpu/drm/i915/i915_gem_request.c
> @@ -23,6 +23,7 @@
>    */
>   
>   #include <linux/prefetch.h>
> +#include <linux/fence-array.h>
>   
>   #include "i915_drv.h"
>   
> @@ -495,6 +496,45 @@ i915_gem_request_await_request(struct drm_i915_gem_request *to,
>   	return 0;
>   }
>   
> +int
> +i915_gem_request_await_fence(struct drm_i915_gem_request *req,
> +			     struct fence *fence)
> +{
> +	struct fence_array *array;
> +	int ret;
> +	int i;
> +
> +	if (test_bit(FENCE_FLAG_SIGNALED_BIT, &fence->flags))
> +		return 0;
> +
> +	if (fence_is_i915(fence))
> +		return i915_gem_request_await_request(req, to_request(fence));
> +
> +	if (!fence_is_array(fence)) {
> +		ret = i915_sw_fence_await_dma_fence(&req->submit,
> +						    fence, 10*HZ,
> +						    GFP_KERNEL);
> +		return ret < 0 ? ret : 0;
> +	}
> +
> +	array = to_fence_array(fence);
> +	for (i = 0; i < array->num_fences; i++) {
> +		struct fence *child = array->fences[i];

1. What is the advantage in manually waiting on array elements rather 
than just the array? Is the existance of signal_on_any a problem?

2. Can child be another array?

Regards,

Tvrtko

> +
> +		if (fence_is_i915(child))
> +			ret = i915_gem_request_await_request(req,
> +							     to_request(child));
> +		else
> +			ret = i915_sw_fence_await_dma_fence(&req->submit,
> +							    child, 10*HZ,
> +							    GFP_KERNEL);
> +		if (ret < 0)
> +			return ret;
> +	}
> +
> +	return 0;
> +}
> +
>   /**
>    * i915_gem_request_await_object - set this request to (async) wait upon a bo
>    *
> diff --git a/drivers/gpu/drm/i915/i915_gem_request.h b/drivers/gpu/drm/i915/i915_gem_request.h
> index 974bd7bcc801..c85a3d82febf 100644
> --- a/drivers/gpu/drm/i915/i915_gem_request.h
> +++ b/drivers/gpu/drm/i915/i915_gem_request.h
> @@ -214,6 +214,8 @@ int
>   i915_gem_request_await_object(struct drm_i915_gem_request *to,
>   			      struct drm_i915_gem_object *obj,
>   			      bool write);
> +int i915_gem_request_await_fence(struct drm_i915_gem_request *req,
> +				 struct fence *fence);
>   
>   void __i915_add_request(struct drm_i915_gem_request *req, bool flush_caches);
>   #define i915_add_request(req) \

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