Re: [PATCH] drm/i915: Serialise presentation with imported dmabufs

[Daniel Vetter <daniel@ffwll.ch>]

On Tue, Jun 14, 2016 at 04:03:57PM +0100, Chris Wilson wrote:
> obj->base.dma_buf represents a dma-buf exported from this object (for
> use by others). On the contrary, ob->base.import_attach represents the
> source dma-buf that was used to create this object (if any). When
> serialising with third parties, we want to wait on their rendering via
> the import attachment (and not our own via the dma_buf export).
> 
> Note that for an object exported from i915 and passed to another i915
> client, we do not create the import attachment and so serialisation will
> use our native paths.

But that would break it, if the foreign object attaches a some fence to
the reservation. We need things to work both ways, and that is done by
having a reservation pointer, where we either store our own per-bo lock +
list of reservations, or the imported one from the other driver.

A bit much, but interim we'd need at least both base.dma_buf and
base.import_attach.

Also, we should just extract the fence, and wait on that later on in the
atomic path.
-Daniel

> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Alex Goins <agoins@nvidia.com>
> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>


> ---
>  drivers/gpu/drm/i915/intel_display.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index 801e4c17dd8d..cbaa2e6f7679 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -11425,8 +11425,8 @@ static bool use_mmio_flip(struct intel_engine_cs *engine,
>  		return true;
>  	else if (i915.enable_execlists)
>  		return true;
> -	else if (obj->base.dma_buf &&
> -		 !reservation_object_test_signaled_rcu(obj->base.dma_buf->resv,
> +	else if (obj->base.import_attach &&
> +		 !reservation_object_test_signaled_rcu(obj->base.import_attach->dmabuf->resv,
>  						       false))
>  		return true;
>  	else
> @@ -11526,8 +11526,8 @@ static void intel_mmio_flip_work_func(struct work_struct *w)
>  					    &dev_priv->rps.mmioflips));
>  
>  	/* For framebuffer backed by dmabuf, wait for fence */
> -	if (obj->base.dma_buf)
> -		WARN_ON(reservation_object_wait_timeout_rcu(obj->base.dma_buf->resv,
> +	if (obj->base.import_attach)
> +		WARN_ON(reservation_object_wait_timeout_rcu(obj->base.import_attach->dmabuf->resv,
>  							    false, false,
>  							    MAX_SCHEDULE_TIMEOUT) < 0);
>  
> @@ -13952,10 +13952,10 @@ intel_prepare_plane_fb(struct drm_plane *plane,
>  	}
>  
>  	/* For framebuffer backed by dmabuf, wait for fence */
> -	if (obj && obj->base.dma_buf) {
> +	if (obj && obj->base.import_attach) {
>  		long lret;
>  
> -		lret = reservation_object_wait_timeout_rcu(obj->base.dma_buf->resv,
> +		lret = reservation_object_wait_timeout_rcu(obj->base.import_attach->dmabuf->resv,
>  							   false, true,
>  							   MAX_SCHEDULE_TIMEOUT);
>  		if (lret == -ERESTARTSYS)
> -- 
> 2.8.1
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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