drm/vmwgfx: Add support for imported Fence File Descriptor

This allows vmwgfx to wait on a fence created by another
device.

v2:
* Remove special handling for vmwgfx fence and just use dma_fence_wait()
* Use interruptible waits
* Added function documentation

Signed-off-by: Sinclair Yeh <syeh@vmware.com>
Reviewed-by: Deepak Singh Rawat <drawat@vmware.com>
Reviewed-by: Thomas Hellstrom <thellstrom@vmware.com>

drivers/gpu/drm/vmwgfx/vmwgfx_fence.c

@@ -644,6 +644,51 @@ out_no_object:
 }
 
 
+/**
+ * vmw_wait_dma_fence - Wait for a dma fence
+ *
+ * @fman: pointer to a fence manager
+ * @fence: DMA fence to wait on
+ *
+ * This function handles the case when the fence is actually a fence
+ * array.  If that's the case, it'll wait on each of the child fence
+ */
+int vmw_wait_dma_fence(struct vmw_fence_manager *fman,
+		       struct dma_fence *fence)
+{
+	struct dma_fence_array *fence_array;
+	int ret = 0;
+	int i;
+
+
+	if (dma_fence_is_signaled(fence))
+		return 0;
+
+	if (!dma_fence_is_array(fence))
+		return dma_fence_wait(fence, true);
+
+	/* From i915: Note that if the fence-array was created in
+	 * signal-on-any mode, we should *not* decompose it into its individual
+	 * fences. However, we don't currently store which mode the fence-array
+	 * is operating in. Fortunately, the only user of signal-on-any is
+	 * private to amdgpu and we should not see any incoming fence-array
+	 * from sync-file being in signal-on-any mode.
+	 */
+
+	fence_array = to_dma_fence_array(fence);
+	for (i = 0; i < fence_array->num_fences; i++) {
+		struct dma_fence *child = fence_array->fences[i];
+
+		ret = dma_fence_wait(child, true);
+
+		if (ret < 0)
+			return ret;
+	}
+
+	return 0;
+}
+
+
 /**
  * vmw_fence_fifo_down - signal all unsignaled fence objects.
  */