[RFC v2 1/8] dma-buf/fence: add fence_collection fences

[Gustavo Padovan]

From: Gustavo Padovan <gustavo.padovan@xxxxxxxxxxxxxxx>

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 on DRM drivers. So even if there are many
fences in the sync_file that needs to waited for a commit to happen,
they all get added to the fence_collection and passed for DRM use as
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, so
fence_is_later() and fence_later() are not meant to be called with
fence_collections fences.

v2: Comments by Daniel Vetter:
	- merge fence_collection_init() and fence_collection_add()
	- only add callbacks at ->enable_signalling()
	- remove fence_collection_put()
	- check for type on to_fence_collection()
	- adjust fence_is_later() and fence_later() to WARN_ON() if they
	are used with collection fences.

Signed-off-by: Gustavo Padovan <gustavo.padovan@xxxxxxxxxxxxxxx>
---
 drivers/dma-buf/Makefile           |   2 +-
 drivers/dma-buf/fence-collection.c | 159 +++++++++++++++++++++++++++++++++++++
 drivers/dma-buf/fence.c            |   2 +-
 include/linux/fence-collection.h   |  73 +++++++++++++++++
 include/linux/fence.h              |   9 +++
 5 files changed, 243 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 4a424ec..52f818f 100644
--- a/drivers/dma-buf/Makefile
+++ b/drivers/dma-buf/Makefile
@@ -1,2 +1,2 @@
-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
diff --git a/drivers/dma-buf/fence-collection.c b/drivers/dma-buf/fence-collection.c
new file mode 100644
index 0000000..88872e5
--- /dev/null
+++ b/drivers/dma-buf/fence-collection.c
@@ -0,0 +1,159 @@
+/*
+ * fence-collection: aggregate fences to be waited together
+ *
+ * Copyright (C) 2016 Collabora Ltd
+ * Authors:
+ *	Gustavo Padovan <gustavo@xxxxxxxxxxx>
+ *
+ * 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 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);
+}
+
+static bool fence_collection_enable_signaling(struct fence *fence)
+{
+	struct fence_collection *collection = to_fence_collection(fence);
+	int i;
+
+	for (i = 0 ; i < collection->num_fences ; i++) {
+		if (fence_add_callback(collection->fences[i].fence,
+				       &collection->fences[i].cb,
+				       collection_check_cb_func)) {
+			atomic_dec(&collection->num_pending_fences);
+			return false;
+		}
+	}
+
+	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_put(collection->fences[i].fence);
+
+	kfree(collection->fences);
+	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;
+
+	if (test_bit(FENCE_FLAG_SIGNALED_BIT, &fence->flags))
+		return timeout;
+
+	fence_enable_sw_signaling(fence);
+
+	for (i = 0 ; i < collection->num_fences ; i++) {
+		if (test_bit(FENCE_FLAG_SIGNALED_BIT, &fence->flags))
+			return timeout;
+
+		timeout = fence_wait(collection->fences[i].fence, intr);
+		if (timeout < 0)
+			return timeout;
+	}
+
+	return timeout;
+}
+
+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,
+};
+
+/**
+ * fence_collection_create - Create a custom fence collection
+ * is signaled
+ * @num_fences:	[in]	number of fences to add in the collection
+ * @cb:		[in]	cb array containing the fences for the collection
+ *
+ * Allocate a fence_collection and initialize the base fence with fence_init()
+ * and FENCE_NO_CONTEXT. It also inits all fence_collections specific fields
+ * and return the created fence_collection. In case of error it returns NULL.
+ *
+ * The caller should allocte the fence_collection_cb array with num_fences size
+ * and fill the fence fields with all the fences it wants to add to the
+ * collection.
+ *
+ * Collections have no context, thus fence_later() and fence_is_later() shall
+ * not be used with fence_collection.
+ *
+ * fence_put() on the base fence should be used to release the collection.
+ */
+struct fence_collection *fence_collection_create(int num_fences,
+						 struct fence_collection_cb *cb)
+{
+	struct fence_collection *collection;
+	int i;
+
+	collection = kzalloc(sizeof(*collection), GFP_KERNEL);
+	if (!collection)
+		return NULL;
+
+	spin_lock_init(&collection->lock);
+	fence_init(&collection->base, &fence_collection_ops, &collection->lock,
+		   FENCE_NO_CONTEXT, 0);
+
+	collection->fences = cb;
+	collection->num_fences = num_fences;
+	atomic_set(&collection->num_pending_fences, num_fences);
+
+	for (i = 0 ; i < collection->num_fences ; i++) {
+		fence_get(collection->fences[i].fence);
+		collection->fences[i].collection = collection;
+	}
+
+	return collection;
+}
+EXPORT_SYMBOL(fence_collection_create);
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..4087622
--- /dev/null
+++ b/include/linux/fence-collection.h
@@ -0,0 +1,73 @@
+/*
+ * fence-collection: aggregates fence to be waited together
+ *
+ * Copyright (C) 2016 Collabora Ltd
+ * Authors:
+ *	Gustavo Padovan <gustavo@xxxxxxxxxxx>
+ *
+ * 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 - callback for fence_add_callback
+ * @cb: the base fence_cb object
+ * @fence: fence we are storing in the collection
+ * @collection: collection the fence belongs to
+ *
+ * This struct is at the same time the storage for the fences in the
+ * collection and the struct we pass to fence_add_callback()
+ */
+struct fence_collection_cb {
+	struct fence_cb cb;
+	struct fence *fence;
+	struct fence_collection *collection;
+};
+
+/**
+ * struct fence_collection - fence to represent a collection of fences
+ * @base: fence base class
+ * @lock: spinlock for fence handling
+ * @num_pending_fences: fences in the collection not signaled yet
+ * @num_fences: number of fences in the collection
+ * @fences: ponteir to fence_collection_cb with data about the fences
+ */
+struct fence_collection {
+	struct fence base;
+
+	spinlock_t lock;
+	atomic_t num_pending_fences;
+	int num_fences;
+	struct fence_collection_cb *fences;
+};
+
+extern const struct fence_ops fence_collection_ops;
+
+/**
+ * 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)
+{
+	if (fence->ops != &fence_collection_ops)
+		return NULL;
+	return container_of(fence, struct fence_collection, base);
+}
+
+struct fence_collection *fence_collection_create(int num_fences,
+						struct fence_collection_cb *cb);
+#endif /* __LINUX_FENCE_COLLECTION_H */
diff --git a/include/linux/fence.h b/include/linux/fence.h
index 5aa95eb..184ce79 100644
--- a/include/linux/fence.h
+++ b/include/linux/fence.h
@@ -30,6 +30,9 @@
 #include <linux/printk.h>
 #include <linux/rcupdate.h>
 
+/* context number for fences without context, e.g: fence_collection */
+#define FENCE_NO_CONTEXT 0
+
 struct fence;
 struct fence_ops;
 struct fence_cb;
@@ -292,6 +295,9 @@ static inline bool fence_is_later(struct fence *f1, struct fence *f2)
 	if (WARN_ON(f1->context != f2->context))
 		return false;
 
+	if (WARN_ON(f1->context == FENCE_NO_CONTEXT))
+		return false;
+
 	return (int)(f1->seqno - f2->seqno) > 0;
 }
 
@@ -309,6 +315,9 @@ static inline struct fence *fence_later(struct fence *f1, struct fence *f2)
 	if (WARN_ON(f1->context != f2->context))
 		return NULL;
 
+	if (WARN_ON(f1->context == FENCE_NO_CONTEXT))
+		return NULL;
+
 	/*
 	 * can't check just FENCE_FLAG_SIGNALED_BIT here, it may never have been
 	 * set if enable_signaling wasn't called, and enabling that here is
-- 
2.5.5