Re: [Linaro-mm-sig] [PATCH 6/7] reservation: cross-device reservation support

+/**

• • 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);