Re: [PATCH 1/2] dma-buf/fence: add fence_collection fences

Chris Wilson
2016-05-18T22:57:53Z

On Wed, May 18, 2016 at 05:59:52PM -0300, Gustavo Padovan wrote:
> +static void collection_check_cb_func(struct fence *fence, struct fence_cb *cb)
> +{
> + struct fence_collection_cb *f_cb;
> + struct fence_collection *collection;
> +
> + f_cb = container_of(cb, struct fence_collection_cb, cb);
> + collection = f_cb->collection;
> +
> + if (atomic_dec_and_test(&collection->num_pending_fences))
> + fence_signal(&collection->base);
> +}
> +
> +static bool fence_collection_enable_signaling(struct fence *fence)
> +{
> + struct fence_collection *collection = to_fence_collection(fence);
> + int i;
> +
> + for (i = 0 ; i < collection->num_fences ; i++) {
> + if (fence_add_callback(collection->fences[i].fence,
> + &collection->fences[i].cb,
> + collection_check_cb_func)) {
> + atomic_dec(&collection->num_pending_fences);
> + }
> + }

We don't always have a convenient means to preallocate an array of
fences to use. Keeping a list of fences in addition to the array would
be easier to user in many circumstances.

Just means we need a

struct fence_collection_entry {
struct fence *fence;
struct list_head link;
};

int fence_collection_add(struct fence *_collection,
struct fence *fence)
{
struct fence_collection *collection =
to_fence_collection(_collection);
struct fence_collection_entry *entry;

entry = kmalloc(sizeof(*entry), GFP_KERNEL);
if (!entry)
return -ENOMEM;

entry->fence = fence_get(fence);
list_add_tail(&entry->link, &collection->fence_list);
atomic_inc(&collection->num_pending_fences);

return 0;
}

and a couple of list iterations as well as walking the arrays.

(This fence_collection_add() needs to be documented to only be valid
from the constructing thread before the fence is sealed for export/use.)
-Chris

--
Chris Wilson, Intel Open Source Technology Centre