Almost everyone uses dma_fence_default_wait.

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

Reviewed-by: Christian König <christian.koe...@amd.com> (v1)
Signed-off-by: Daniel Vetter <daniel.vet...@ffwll.ch>
Cc: Chris Wilson <ch...@chris-wilson.co.uk>
Cc: Sumit Semwal <sumit.sem...@linaro.org>
Cc: Gustavo Padovan <gust...@padovan.org>
Cc: linux-me...@vger.kernel.org
Cc: linaro-mm-...@lists.linaro.org
---
 drivers/dma-buf/dma-fence-array.c |  1 -
 drivers/dma-buf/dma-fence.c       |  8 +++++---
 drivers/dma-buf/sw_sync.c         |  1 -
 include/linux/dma-fence.h         | 13 ++++++++-----
 4 files changed, 13 insertions(+), 10 deletions(-)

diff --git a/drivers/dma-buf/dma-fence-array.c 
b/drivers/dma-buf/dma-fence-array.c
index dd1edfb27b61..a8c254497251 100644
--- a/drivers/dma-buf/dma-fence-array.c
+++ b/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);
diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c
index 59049375bd19..41ec19c9efc7 100644
--- a/drivers/dma-buf/dma-fence.c
+++ b/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);
-       ret = fence->ops->wait(fence, intr, timeout);
+       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;
 }
@@ -562,8 +565,7 @@ 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;
diff --git a/drivers/dma-buf/sw_sync.c b/drivers/dma-buf/sw_sync.c
index 3d78ca89a605..53c1d6d36a64 100644
--- a/drivers/dma-buf/sw_sync.c
+++ b/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,
diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h
index c053d19e1e24..02dba8cd033d 100644
--- a/include/linux/dma-fence.h
+++ b/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);
-- 
2.17.0

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