[PATCH 5/8] sync_file: add support for a semaphore object

[Dave Airlie]

On 11 April 2017 at 17:50, Chris Wilson <chris at chris-wilson.co.uk> wrote:
> On Tue, Apr 11, 2017 at 01:22:17PM +1000, Dave Airlie wrote:
>> From: Dave Airlie <airlied at redhat.com>
>>
>> This object can be used to implement the Vulkan semaphores.
>>
>> The object behaviour differs from fence, in that you can
>> replace the underlying fence, and you cannot merge semaphores.
>>
>> Signed-off-by: Dave Airlie <airlied at redhat.com>
>> ---
>> +/**
>> + * sync_file_replace_fence - replace the fence related to the sync_file
>> + * @sync_file:        sync file to replace fence in
>> + * @fence: fence to replace with (or NULL for no fence).
>> + * Returns previous fence.
>> + */
>> +struct dma_fence *sync_file_replace_fence(struct sync_file *sync_file,
>> +                                       struct dma_fence *fence)
>> +{
>> +     struct dma_fence *ret_fence = NULL;
>> +
>> +     if (sync_file->type != SYNC_FILE_TYPE_SEMAPHORE)
>> +             return NULL;
>> +
>> +     if (fence)
>> +             dma_fence_get(fence);
>> +
>> +     mutex_lock(&sync_file->lock);
>> +
>> +     ret_fence = sync_file_get_fence_locked(sync_file);
>> +     if (ret_fence) {
>> +             if (test_bit(POLL_ENABLED, &ret_fence->flags))
>> +                     dma_fence_remove_callback(ret_fence, &sync_file->cb);
>> +     }
>
> Fails when sync_file_replace_fence is passed sync_file->fence.

Not sure what the best semantics are there, any opinions on barring
wakeups/polling on semaphore sync_files, and just punting this
until we need it.

It would definitely simplify things.

Dave.