[3/3] dma-buf: generalize fence merging

diff --git a/drivers/dma-buf/dma-fence-unwrap.c b/drivers/dma-buf/dma-fence-unwrap.c
index 711be125428c..c9becc74896d 100644
--- a/drivers/dma-buf/dma-fence-unwrap.c
+++ b/drivers/dma-buf/dma-fence-unwrap.c
@@ -11,6 +11,7 @@ 
 #include <linux/dma-fence-array.h>
 #include <linux/dma-fence-chain.h>
 #include <linux/dma-fence-unwrap.h>
+#include <linux/slab.h>
 
 /* Internal helper to start new array iteration, don't use directly */
 static struct dma_fence *
@@ -57,3 +58,97 @@  struct dma_fence *dma_fence_unwrap_next(struct dma_fence_unwrap *cursor)
 	return __dma_fence_unwrap_array(cursor);
 }
 EXPORT_SYMBOL_GPL(dma_fence_unwrap_next);
+
+/* Implementation for the dma_fence_merge() marco, don't use directly */
+struct dma_fence *__dma_fence_merge(unsigned int num_fences,
+				    struct dma_fence **fences,
+				    struct dma_fence_unwrap *iter)
+{
+	struct dma_fence_array *result;
+	struct dma_fence *tmp, **array;
+	unsigned int i, count;
+
+	count = 0;
+	for (i = 0; i < num_fences; ++i) {
+		dma_fence_unwrap_for_each(tmp, &iter[i], fences[i])
+			if (!dma_fence_is_signaled(tmp))
+				++count;
+	}
+
+	if (count == 0)
+		return dma_fence_get_stub();
+
+	if (count > INT_MAX)
+		return NULL;
+
+	array = kmalloc_array(count, sizeof(*array), GFP_KERNEL);
+	if (!array)
+		return NULL;
+
+	/*
+	 * We can't guarantee that inpute fences are ordered by context, but
+	 * it is still quite likely when this function is used multiple times.
+	 * So attempt to order the fences by context as we pass over them and
+	 * merge fences with the same context.
+	 */
+	for (i = 0; i < num_fences; ++i)
+		fences[i] = dma_fence_unwrap_first(fences[i], &iter[i]);
+
+	count = 0;
+	do {
+		unsigned int sel;
+
+restart:
+		tmp = NULL;
+		for (i = 0; i < num_fences; ++i) {
+			struct dma_fence *next = fences[i];
+
+			if (!next || dma_fence_is_signaled(next))
+				continue;
+
+			if (!tmp || tmp->context > next->context) {
+				tmp = next;
+				sel = i;
+
+			} else if (tmp->context < next->context) {
+				continue;
+
+			} else if (dma_fence_is_later(tmp, next)) {
+				fences[i] = dma_fence_unwrap_next(&iter[i]);
+				goto restart;
+			} else {
+				fences[sel] = dma_fence_unwrap_next(&iter[sel]);
+				goto restart;
+			}
+		}
+
+		if (tmp) {
+			array[count++] = dma_fence_get(tmp);
+			fences[sel] = dma_fence_unwrap_next(&iter[sel]);
+		}
+	} while (tmp);
+
+	if (count == 0) {
+		tmp = dma_fence_get_stub();
+		goto return_tmp;
+	}
+
+	if (count == 1) {
+		tmp = array[0];
+		goto return_tmp;
+	}
+
+	result = dma_fence_array_create(count, array,
+					dma_fence_context_alloc(1),
+					1, false);
+	if (!result) {
+		tmp = NULL;
+		goto return_tmp;
+	}
+	return &result->base;
+
+return_tmp:
+	kfree(array);
+	return tmp;
+}
+EXPORT_SYMBOL_GPL(__dma_fence_merge);
diff --git a/drivers/dma-buf/st-dma-fence-unwrap.c b/drivers/dma-buf/st-dma-fence-unwrap.c
index 59628add93f5..23ab134417ed 100644
--- a/drivers/dma-buf/st-dma-fence-unwrap.c
+++ b/drivers/dma-buf/st-dma-fence-unwrap.c
@@ -240,6 +240,52 @@  static int unwrap_chain_array(void *arg)
 	return err;
 }
 
+static int unwrap_merge(void *arg)
+{
+	struct dma_fence *fence, *f1, *f2, *f3;
+	struct dma_fence_unwrap iter;
+	int err = 0;
+
+	f1 = mock_fence();
+	if (!f1)
+		return -ENOMEM;
+
+	f2 = mock_fence();
+	if (!f2) {
+		err = -ENOMEM;
+		goto error_put_f1;
+	}
+
+	f3 = dma_fence_merge(f1, f2);
+	if (!f3) {
+		err = -ENOMEM;
+		goto error_put_f2;
+	}
+
+	dma_fence_unwrap_for_each(fence, &iter, f3) {
+		if (fence == f1) {
+			f1 = NULL;
+		} else if (fence == f2) {
+			f2 = NULL;
+		} else {
+			pr_err("Unexpected fence!\n");
+			err = -EINVAL;
+		}
+	}
+
+	if (f1 || f2) {
+		pr_err("Not all fences seen!\n");
+		err = -EINVAL;
+	}
+
+	dma_fence_put(f3);
+error_put_f2:
+	dma_fence_put(f2);
+error_put_f1:
+	dma_fence_put(f1);
+	return err;
+}
+
 int dma_fence_unwrap(void)
 {
 	static const struct subtest tests[] = {
@@ -247,6 +293,7 @@  int dma_fence_unwrap(void)
 		SUBTEST(unwrap_array),
 		SUBTEST(unwrap_chain),
 		SUBTEST(unwrap_chain_array),
+		SUBTEST(unwrap_merge),
 	};
 
 	return subtests(tests, NULL);
diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c
index 0fe564539166..fe149d7e3ce2 100644
--- a/drivers/dma-buf/sync_file.c
+++ b/drivers/dma-buf/sync_file.c
@@ -146,50 +146,6 @@  char *sync_file_get_name(struct sync_file *sync_file, char *buf, int len)
 	return buf;
 }
 
-static int sync_file_set_fence(struct sync_file *sync_file,
-			       struct dma_fence **fences, int num_fences)
-{
-	struct dma_fence_array *array;
-
-	/*
-	 * The reference for the fences in the new sync_file and held
-	 * in add_fence() during the merge procedure, so for num_fences == 1
-	 * we already own a new reference to the fence. For num_fence > 1
-	 * we own the reference of the dma_fence_array creation.
-	 */
-
-	if (num_fences == 0) {
-		sync_file->fence = dma_fence_get_stub();
-		kfree(fences);
-
-	} else if (num_fences == 1) {
-		sync_file->fence = fences[0];
-		kfree(fences);
-
-	} else {
-		array = dma_fence_array_create(num_fences, fences,
-					       dma_fence_context_alloc(1),
-					       1, false);
-		if (!array)
-			return -ENOMEM;
-
-		sync_file->fence = &array->base;
-	}
-
-	return 0;
-}
-
-static void add_fence(struct dma_fence **fences,
-		      int *i, struct dma_fence *fence)
-{
-	fences[*i] = fence;
-
-	if (!dma_fence_is_signaled(fence)) {
-		dma_fence_get(fence);
-		(*i)++;
-	}
-}
-
 /**
  * sync_file_merge() - merge two sync_files
  * @name:	name of new fence
@@ -203,84 +159,21 @@  static void add_fence(struct dma_fence **fences,
 static struct sync_file *sync_file_merge(const char *name, struct sync_file *a,
 					 struct sync_file *b)
 {
-	struct dma_fence *a_fence, *b_fence, **fences;
-	struct dma_fence_unwrap a_iter, b_iter;
-	unsigned int index, num_fences;
 	struct sync_file *sync_file;
+	struct dma_fence *fence;
 
 	sync_file = sync_file_alloc();
 	if (!sync_file)
 		return NULL;
 
-	num_fences = 0;
-	dma_fence_unwrap_for_each(a_fence, &a_iter, a->fence)
-		++num_fences;
-	dma_fence_unwrap_for_each(b_fence, &b_iter, b->fence)
-		++num_fences;
-
-	if (num_fences > INT_MAX)
-		goto err_free_sync_file;
-
-	fences = kcalloc(num_fences, sizeof(*fences), GFP_KERNEL);
-	if (!fences)
-		goto err_free_sync_file;
-
-	/*
-	 * We can't guarantee that fences in both a and b are ordered, but it is
-	 * still quite likely.
-	 *
-	 * So attempt to order the fences as we pass over them and merge fences
-	 * with the same context.
-	 */
-
-	index = 0;
-	for (a_fence = dma_fence_unwrap_first(a->fence, &a_iter),
-	     b_fence = dma_fence_unwrap_first(b->fence, &b_iter);
-	     a_fence || b_fence; ) {
-
-		if (!b_fence) {
-			add_fence(fences, &index, a_fence);
-			a_fence = dma_fence_unwrap_next(&a_iter);
-
-		} else if (!a_fence) {
-			add_fence(fences, &index, b_fence);
-			b_fence = dma_fence_unwrap_next(&b_iter);
-
-		} else if (a_fence->context < b_fence->context) {
-			add_fence(fences, &index, a_fence);
-			a_fence = dma_fence_unwrap_next(&a_iter);
-
-		} else if (b_fence->context < a_fence->context) {
-			add_fence(fences, &index, b_fence);
-			b_fence = dma_fence_unwrap_next(&b_iter);
-
-		} else if (__dma_fence_is_later(a_fence->seqno, b_fence->seqno,
-						a_fence->ops)) {
-			add_fence(fences, &index, a_fence);
-			a_fence = dma_fence_unwrap_next(&a_iter);
-			b_fence = dma_fence_unwrap_next(&b_iter);
-
-		} else {
-			add_fence(fences, &index, b_fence);
-			a_fence = dma_fence_unwrap_next(&a_iter);
-			b_fence = dma_fence_unwrap_next(&b_iter);
-		}
+	fence = dma_fence_merge(a->fence, b->fence);
+	if (!fence) {
+		fput(sync_file->file);
+		return NULL;
 	}
-
-	if (sync_file_set_fence(sync_file, fences, index) < 0)
-		goto err_put_fences;
-
+	sync_file->fence = fence;
 	strlcpy(sync_file->user_name, name, sizeof(sync_file->user_name));
 	return sync_file;
-
-err_put_fences:
-	while (index)
-		dma_fence_put(fences[--index]);
-	kfree(fences);
-
-err_free_sync_file:
-	fput(sync_file->file);
-	return NULL;
 }
 
 static int sync_file_release(struct inode *inode, struct file *file)
diff --git a/include/linux/dma-fence-unwrap.h b/include/linux/dma-fence-unwrap.h
index e7c219da4ed7..7c0fab318301 100644
--- a/include/linux/dma-fence-unwrap.h
+++ b/include/linux/dma-fence-unwrap.h
@@ -48,4 +48,28 @@  struct dma_fence *dma_fence_unwrap_next(struct dma_fence_unwrap *cursor);
 	for (fence = dma_fence_unwrap_first(head, cursor); fence;	\
 	     fence = dma_fence_unwrap_next(cursor))
 
+struct dma_fence *__dma_fence_merge(unsigned int num_fences,
+				    struct dma_fence **fences,
+				    struct dma_fence_unwrap *cursors);
+
+/**
+ * dma_fence_merge - unwrap and merge fences
+ *
+ * All fences given as parameters are unwrapped and merged back together as flat
+ * dma_fence_array. Useful if multiple containers need to be merged together.
+ *
+ * Implemented as a macro to allocate the necessary arrays on the stack and
+ * account the stack frame size to the caller.
+ *
+ * Returns NULL on memory allocation failure, a dma_fence object representing
+ * all the given fences otherwise.
+ */
+#define dma_fence_merge(...)					\
+	({							\
+		struct dma_fence *__f[] = { __VA_ARGS__ };	\
+		struct dma_fence_unwrap __c[ARRAY_SIZE(__f)];	\
+								\
+		__dma_fence_merge(ARRAY_SIZE(__f), __f, __c);	\
+	})
+
 #endif