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SubjectRe: [Linaro-mm-sig] [PATCH 6/7] reservation: cross-device reservation support
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> +/**
> + * ticket_commit - commit a reservation with a new fence
> + * @ticket: [in] the reservation_ticket returned by
> + * ticket_reserve
> + * @entries: [in] a linked list of struct reservation_entry
> + * @fence: [in] the fence that indicates completion
> + *
> + * This function will call reservation_ticket_fini, no need
> + * to do it manually.
> + *
> + * This function should be called after a hardware command submission is
> + * completed succesfully. The fence is used to indicate completion of
> + * those commands.
> + */
> +void
> +ticket_commit(struct reservation_ticket *ticket,
> + struct list_head *entries, struct fence *fence)
> +{
> + struct list_head *cur;
> +
> + if (list_empty(entries))
> + return;
> +
> + if (WARN_ON(!fence)) {
> + ticket_backoff(ticket, entries);
> + return;
> + }
> +
> + list_for_each(cur, entries) {
> + struct reservation_object *bo;
> + bool shared;
> +
> + reservation_entry_get(cur, &bo, &shared);
> +
> + if (!shared) {
> + int i;
> + for (i = 0; i < bo->fence_shared_count; ++i) {
> + fence_put(bo->fence_shared[i]);
> + bo->fence_shared[i] = NULL;
> + }
> + bo->fence_shared_count = 0;
> + if (bo->fence_excl)
> + fence_put(bo->fence_excl);
> +
> + bo->fence_excl = fence;
> + } else {
> + if (WARN_ON(bo->fence_shared_count >=
> + ARRAY_SIZE(bo->fence_shared))) {
> + mutex_unreserve_unlock(&bo->lock);
> + continue;
> + }
> +
> + bo->fence_shared[bo->fence_shared_count++] = fence;
> + }

Hi,

I got some questions to fence_excl and fence_shared. At the above
code, if bo->fence_excl is not NULL then it puts bo->fence_excl and
sets a new fence to it. This seems like that someone that committed a
new fence, wants to access the given dmabuf exclusively even if
someone is accessing the given dmabuf.

On the other hand, in case of fence_shared, someone wants to access
that dmabuf non-exclusively. So this case seems like that the given
dmabuf could be accessed by two more devices. So I guess that the
fence_excl could be used for write access(may need buffer sync like
blocking) and read access for the fence_shared(may not need buffer
sync). I'm not sure that I understand these two things correctly so
could you please give me more comments for them?

Thanks,
Inki Dae

> + fence_get(fence);
> +
> + mutex_unreserve_unlock(&bo->lock);
> + }
> + reservation_ticket_fini(ticket);
> +}
> +EXPORT_SYMBOL(ticket_commit);


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