dma-buf/dma-fence: Extract __dma_fence_is_later()

Often we have the task of comparing two seqno known to be on the same
context, so provide a common __dma_fence_is_later().
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: Sean Paul <seanpaul@chromium.org>
Cc: Gustavo Padovan <gustavo@padovan.org>
Reviewed-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170629125930.821-1-chris@chris-wilson.co.uk

include/linux/dma-fence.h

@@ -335,6 +335,19 @@ dma_fence_is_signaled(struct dma_fence *fence)
 	return false;
 }
 
+/**
+ * __dma_fence_is_later - return if f1 is chronologically later than f2
+ * @f1:	[in]	the first fence's seqno
+ * @f2:	[in]	the second fence's seqno from the same context
+ *
+ * Returns true if f1 is chronologically later than f2. Both fences must be
+ * from the same context, since a seqno is not common across contexts.
+ */
+static inline bool __dma_fence_is_later(u32 f1, u32 f2)
+{
+	return (int)(f1 - f2) > 0;
+}
+
 /**
  * dma_fence_is_later - return if f1 is chronologically later than f2
  * @f1:	[in]	the first fence from the same context
@@ -349,7 +362,7 @@ static inline bool dma_fence_is_later(struct dma_fence *f1,
 	if (WARN_ON(f1->context != f2->context))
 		return false;
 
-	return (int)(f1->seqno - f2->seqno) > 0;
+	return __dma_fence_is_later(f1->seqno, f2->seqno);
 }
 
 /**