[RFC 1/8] dma-buf/fence: add fence_collection fences

[Gustavo Padovan <gustavo@padovan.org>]

From: Gustavo Padovan <gustavo.padovan@collabora.co.uk>

struct fence_collection inherits from struct fence and carries a
collection of fences that needs to be waited together.

It is useful to translate a sync_file to a fence to remove the complexity
of dealing with sync_files from DRM drivers. So even if there are many
fences in the sync_file that needs to waited for a commit to happen
drivers would only worry about a standard struct fence.That means that no
changes needed to any driver besides supporting fences.

fence_collection's fence doesn't belong to any timeline context.

Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
---
 drivers/dma-buf/Makefile           |   2 +-
 drivers/dma-buf/fence-collection.c | 138 +++++++++++++++++++++++++++++++++++++
 drivers/dma-buf/fence.c            |   2 +-
 include/linux/fence-collection.h   |  56 +++++++++++++++
 include/linux/fence.h              |   2 +
 5 files changed, 198 insertions(+), 2 deletions(-)
 create mode 100644 drivers/dma-buf/fence-collection.c
 create mode 100644 include/linux/fence-collection.h

diff --git a/drivers/dma-buf/Makefile b/drivers/dma-buf/Makefile
index 43325a1..30b8464 100644
--- a/drivers/dma-buf/Makefile
+++ b/drivers/dma-buf/Makefile
@@ -1,3 +1,3 @@
-obj-y := dma-buf.o fence.o reservation.o seqno-fence.o
+obj-y := dma-buf.o fence.o reservation.o seqno-fence.o fence-collection.o
 obj-$(CONFIG_SYNC_FILE)		+= sync_file.o sync_timeline.o sync_debug.o
 obj-$(CONFIG_SW_SYNC)		+= sw_sync.o
diff --git a/drivers/dma-buf/fence-collection.c b/drivers/dma-buf/fence-collection.c
new file mode 100644
index 0000000..8a4ecb0
--- /dev/null
+++ b/drivers/dma-buf/fence-collection.c
@@ -0,0 +1,138 @@
+/*
+ * fence-collection: aggregate fences to be waited together
+ *
+ * Copyright (C) 2016 Collabora Ltd
+ * Authors:
+ *	Gustavo Padovan <gustavo@padovan.org>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 as published by
+ * the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ */
+
+#include <linux/export.h>
+#include <linux/slab.h>
+#include <linux/fence-collection.h>
+
+static const char *fence_collection_get_driver_name(struct fence *fence)
+{
+	struct fence_collection *collection = to_fence_collection(fence);
+	struct fence *f = collection->fences[0].fence;
+
+	return f->ops->get_driver_name(fence);
+}
+
+static const char *fence_collection_get_timeline_name(struct fence *fence)
+{
+	return "no context";
+}
+
+static bool fence_collection_enable_signaling(struct fence *fence)
+{
+	struct fence_collection *collection = to_fence_collection(fence);
+
+	return atomic_read(&collection->num_pending_fences);
+}
+
+static bool fence_collection_signaled(struct fence *fence)
+{
+	struct fence_collection *collection = to_fence_collection(fence);
+
+	return (atomic_read(&collection->num_pending_fences) == 0);
+}
+
+static void fence_collection_release(struct fence *fence)
+{
+	struct fence_collection *collection = to_fence_collection(fence);
+	int i;
+
+	for (i = 0 ; i < collection->num_fences ; i++) {
+		fence_remove_callback(collection->fences[i].fence,
+				      &collection->fences[i].cb);
+		fence_put(collection->fences[i].fence);
+	}
+
+	fence_free(fence);
+}
+
+static signed long fence_collection_wait(struct fence *fence, bool intr,
+					 signed long timeout)
+{
+	struct fence_collection *collection = to_fence_collection(fence);
+	int i;
+
+	for (i = 0 ; i < collection->num_fences ; i++) {
+		timeout = fence_wait(collection->fences[i].fence, intr);
+		if (timeout < 0)
+			return timeout;
+	}
+
+	return timeout;
+}
+
+static const struct fence_ops fence_collection_ops = {
+	.get_driver_name = fence_collection_get_driver_name,
+	.get_timeline_name = fence_collection_get_timeline_name,
+	.enable_signaling = fence_collection_enable_signaling,
+	.signaled = fence_collection_signaled,
+	.wait = fence_collection_wait,
+	.release = fence_collection_release,
+};
+
+static void collection_check_cb_func(struct fence *fence, struct fence_cb *cb)
+{
+	struct fence_collection_cb *f_cb;
+	struct fence_collection *collection;
+
+	f_cb = container_of(cb, struct fence_collection_cb, cb);
+	collection = f_cb->collection;
+
+	if (atomic_dec_and_test(&collection->num_pending_fences))
+		fence_signal(&collection->base);
+}
+
+void fence_collection_add(struct fence_collection *collection,
+			  struct fence *fence)
+{
+	int n = collection->num_fences;
+
+	collection->fences[n].collection = collection;
+	collection->fences[n].fence = fence;
+
+	if (fence_add_callback(fence, &collection->fences[n].cb,
+				 collection_check_cb_func))
+		return;
+
+	fence_get(fence);
+
+	collection->num_fences++;
+	atomic_inc(&collection->num_pending_fences);
+}
+
+struct fence_collection *fence_collection_init(int num_fences)
+{
+	struct fence_collection *collection;
+
+	collection = kzalloc(offsetof(struct fence_collection,
+				      fences[num_fences]), GFP_KERNEL);
+	if (!collection)
+		return NULL;
+
+	spin_lock_init(&collection->lock);
+	fence_init(&collection->base, &fence_collection_ops, &collection->lock,
+		   FENCE_NO_CONTEXT, 0);
+
+	return collection;
+}
+EXPORT_SYMBOL(fence_collection_init);
+
+void fence_collection_put(struct fence_collection *collection)
+{
+	fence_put(&collection->base);
+}
+EXPORT_SYMBOL(fence_collection_put);
diff --git a/drivers/dma-buf/fence.c b/drivers/dma-buf/fence.c
index 7b05dbe..486e95c 100644
--- a/drivers/dma-buf/fence.c
+++ b/drivers/dma-buf/fence.c
@@ -35,7 +35,7 @@ EXPORT_TRACEPOINT_SYMBOL(fence_emit);
  * context or not. One device can have multiple separate contexts,
  * and they're used if some engine can run independently of another.
  */
-static atomic_t fence_context_counter = ATOMIC_INIT(0);
+static atomic_t fence_context_counter = ATOMIC_INIT(1);
 
 /**
  * fence_context_alloc - allocate an array of fence contexts
diff --git a/include/linux/fence-collection.h b/include/linux/fence-collection.h
new file mode 100644
index 0000000..a798925
--- /dev/null
+++ b/include/linux/fence-collection.h
@@ -0,0 +1,56 @@
+/*
+ * fence-collection: aggregates fence to be waited together
+ *
+ * Copyright (C) 2016 Collabora Ltd
+ * Authors:
+ *	Gustavo Padovan <gustavo@padovan.org>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 as published by
+ * the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ */
+
+#ifndef __LINUX_FENCE_COLLECTION_H
+#define __LINUX_FENCE_COLLECTION_H
+
+#include <linux/fence.h>
+
+struct fence_collection_cb {
+	struct fence_cb cb;
+	struct fence *fence;
+	struct fence_collection *collection;
+};
+
+struct fence_collection {
+	struct fence base;
+
+	spinlock_t lock;
+	struct fence_cb fence_cb;
+	atomic_t num_pending_fences;
+	int num_fences;
+	struct fence_collection_cb fences[];
+};
+
+/**
+ * to_fence_collection - cast a fence to a fence_collection
+ * @fence: fence to cast to a fence_collection
+ *
+ * Returns NULL if the fence is not a fence_collection,
+ * or the fence_collection otherwise.
+ */
+static inline struct fence_collection * to_fence_collection(struct fence *fence)
+{
+	return container_of(fence, struct fence_collection, base);
+}
+
+struct fence_collection *fence_collection_init(int num_fences);
+void fence_collection_add(struct fence_collection *collection,
+			  struct fence *fence);
+void fence_collection_put(struct fence_collection *collection);
+
+#endif /* __LINUX_FENCE_COLLECTION_H */
diff --git a/include/linux/fence.h b/include/linux/fence.h
index 2b17698..02170dd 100644
--- a/include/linux/fence.h
+++ b/include/linux/fence.h
@@ -30,6 +30,8 @@
 #include <linux/printk.h>
 #include <linux/rcupdate.h>
 
+#define FENCE_NO_CONTEXT 0
+
 struct fence;
 struct fence_ops;
 struct fence_cb;
-- 
2.5.5