dma-fence: Make ->wait callback optional

Almost everyone uses dma_fence_default_wait.

v2: Also remove the BUG_ON(!ops->wait) (Chris).

Reviewed-by: Christian König <christian.koenig@amd.com> (v1)
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: Gustavo Padovan <gustavo@padovan.org>
Cc: linux-media@vger.kernel.org
Cc: linaro-mm-sig@lists.linaro.org
Link: https://patchwork.freedesktop.org/patch/msgid/20180503142603.28513-5-daniel.vetter@ffwll.ch

drivers/dma-buf/dma-fence-array.c

@@ -104,7 +104,6 @@ const struct dma_fence_ops dma_fence_array_ops = {
 	.get_timeline_name = dma_fence_array_get_timeline_name,
 	.enable_signaling = dma_fence_array_enable_signaling,
 	.signaled = dma_fence_array_signaled,
-	.wait = dma_fence_default_wait,
 	.release = dma_fence_array_release,
 };
 EXPORT_SYMBOL(dma_fence_array_ops);

drivers/dma-buf/dma-fence.c

@@ -158,7 +158,10 @@ dma_fence_wait_timeout(struct dma_fence *fence, bool intr, signed long timeout)
 		return -EINVAL;
 
 	trace_dma_fence_wait_start(fence);
+	if (fence->ops->wait)
 		ret = fence->ops->wait(fence, intr, timeout);
+	else
+		ret = dma_fence_default_wait(fence, intr, timeout);
 	trace_dma_fence_wait_end(fence);
 	return ret;
 }
@@ -556,8 +559,7 @@ dma_fence_init(struct dma_fence *fence, const struct dma_fence_ops *ops,
 	       spinlock_t *lock, u64 context, unsigned seqno)
 {
 	BUG_ON(!lock);
-	BUG_ON(!ops || !ops->wait ||
-	       !ops->get_driver_name || !ops->get_timeline_name);
+	BUG_ON(!ops || !ops->get_driver_name || !ops->get_timeline_name);
 
 	kref_init(&fence->refcount);
 	fence->ops = ops;

drivers/dma-buf/sw_sync.c

@@ -188,7 +188,6 @@ static const struct dma_fence_ops timeline_fence_ops = {
 	.get_timeline_name = timeline_fence_get_timeline_name,
 	.enable_signaling = timeline_fence_enable_signaling,
 	.signaled = timeline_fence_signaled,
-	.wait = dma_fence_default_wait,
 	.release = timeline_fence_release,
 	.fence_value_str = timeline_fence_value_str,
 	.timeline_value_str = timeline_fence_timeline_value_str,

include/linux/dma-fence.h

@@ -191,11 +191,14 @@ struct dma_fence_ops {
 	/**
 	 * @wait:
 	 *
-	 * Custom wait implementation, or dma_fence_default_wait.
+	 * Custom wait implementation, defaults to dma_fence_default_wait() if
+	 * not set.
 	 *
-	 * Must not be NULL, set to dma_fence_default_wait for default implementation.
-	 * the dma_fence_default_wait implementation should work for any fence, as long
-	 * as enable_signaling works correctly.
+	 * The dma_fence_default_wait implementation should work for any fence, as long
+	 * as @enable_signaling works correctly. This hook allows drivers to
+	 * have an optimized version for the case where a process context is
+	 * already available, e.g. if @enable_signaling for the general case
+	 * needs to set up a worker thread.
 	 *
 	 * Must return -ERESTARTSYS if the wait is intr = true and the wait was
 	 * interrupted, and remaining jiffies if fence has signaled, or 0 if wait
@@ -203,7 +206,7 @@ struct dma_fence_ops {
 	 * which should be treated as if the fence is signaled. For example a hardware
 	 * lockup could be reported like that.
 	 *
-	 * This callback is mandatory.
+	 * This callback is optional.
 	 */
 	signed long (*wait)(struct dma_fence *fence,
 			    bool intr, signed long timeout);