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

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 ea343f992112..7a92f85a4cec 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;
 }
@@ -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;
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);