Re: [Intel-gfx] [PATCH 2/6] drm/i915: Initialise basic fence before acquiring seqno

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

On 03/02/2020 09:41, Chris Wilson wrote:
> Inside the intel_timeline_get_seqno(), we currently track the retirement
> of the old cachelines by listening to the new request. This requires
> that the new request is ready to be used and so requires a minimum bit
> of initialisation prior to getting the new seqno.
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> Cc: Matthew Auld <matthew.auld@intel.com>
> ---
>   drivers/gpu/drm/i915/i915_request.c | 21 ++++++++++++++-------
>   1 file changed, 14 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c
> index 78a5f5d3c070..f56b046a32de 100644
> --- a/drivers/gpu/drm/i915/i915_request.c
> +++ b/drivers/gpu/drm/i915/i915_request.c
> @@ -595,6 +595,8 @@ static void __i915_request_ctor(void *arg)
>   	i915_sw_fence_init(&rq->submit, submit_notify);
>   	i915_sw_fence_init(&rq->semaphore, semaphore_notify);
>   
> +	dma_fence_init(&rq->fence, &i915_fence_ops, &rq->lock, 0, 0);
> +
>   	rq->file_priv = NULL;
>   	rq->capture_list = NULL;
>   
> @@ -653,25 +655,30 @@ __i915_request_create(struct intel_context *ce, gfp_t gfp)
>   		}
>   	}
>   
> -	ret = intel_timeline_get_seqno(tl, rq, &seqno);
> -	if (ret)
> -		goto err_free;
> -
>   	rq->i915 = ce->engine->i915;
>   	rq->context = ce;
>   	rq->engine = ce->engine;
>   	rq->ring = ce->ring;
>   	rq->execution_mask = ce->engine->mask;
>   
> +	kref_init(&rq->fence.refcount);
> +	rq->fence.flags = 0;
> +	rq->fence.error = 0;
> +	INIT_LIST_HEAD(&rq->fence.cb_list);

One of these fields the previous user leaves in a non-empty state?

Regards,

Tvrtko

> +
> +	ret = intel_timeline_get_seqno(tl, rq, &seqno);
> +	if (ret)
> +		goto err_free;
> +
> +	rq->fence.context = tl->fence_context;
> +	rq->fence.seqno = seqno;
> +
>   	RCU_INIT_POINTER(rq->timeline, tl);
>   	RCU_INIT_POINTER(rq->hwsp_cacheline, tl->hwsp_cacheline);
>   	rq->hwsp_seqno = tl->hwsp_seqno;
>   
>   	rq->rcustate = get_state_synchronize_rcu(); /* acts as smp_mb() */
>   
> -	dma_fence_init(&rq->fence, &i915_fence_ops, &rq->lock,
> -		       tl->fence_context, seqno);
> -
>   	/* We bump the ref for the fence chain */
>   	i915_sw_fence_reinit(&i915_request_get(rq)->submit);
>   	i915_sw_fence_reinit(&i915_request_get(rq)->semaphore);
> 
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