dma-buf/fence: add fence_array fences v6

struct fence_array 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.

To avoid fence_array's fence allocates a new timeline if needed (when
combining fences from different timelines).

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.

v3: - Initialize fence_cb.node at fence init.

    Comments by Chris Wilson:
	- return "unbound" on fence_collection_get_timeline_name()
	- don't stop adding callbacks if one fails
	- remove redundant !! on fence_collection_enable_signaling()
	- remove redundant () on fence_collection_signaled
	- use fence_default_wait() instead

v4 (chk): Rework, simplification and cleanup:
	- Drop FENCE_NO_CONTEXT handling, always allocate a context.
	- Rename to fence_array.
	- Return fixed driver name.
	- Register only one callback at a time.
	- Document that create function takes ownership of array.

v5 (chk): More work and fixes:
	- Avoid deadlocks by adding all callbacks at once again.
	- Stop trying to remove the callbacks.
	- Provide context and sequence number for the array fence.

v6 (chk): Fixes found during testing
	- Fix stupid typo in _enable_signaling().

Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
Acked-by: Sumit Semwal <sumit.semwal@linaro.org>
[danvet: Improve commit message as suggested by Gustavo.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1464786612-5010-3-git-send-email-deathsimple@vodafone.de

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-array.o
 obj-$(CONFIG_SYNC_FILE)		+= sync_file.o

drivers/dma-buf/fence-array.c

@@ -0,0 +1,127 @@
+/*
+ * fence-array: aggregate fences to be waited together
+ *
+ * Copyright (C) 2016 Collabora Ltd
+ * Copyright (C) 2016 Advanced Micro Devices, Inc.
+ * Authors:
+ *	Gustavo Padovan <gustavo@padovan.org>
+ *	Christian König <christian.koenig@amd.com>
+ *
+ * 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-array.h>
+
+static void fence_array_cb_func(struct fence *f, struct fence_cb *cb);
+
+static const char *fence_array_get_driver_name(struct fence *fence)
+{
+	return "fence_array";
+}
+
+static const char *fence_array_get_timeline_name(struct fence *fence)
+{
+	return "unbound";
+}
+
+static void fence_array_cb_func(struct fence *f, struct fence_cb *cb)
+{
+	struct fence_array_cb *array_cb =
+		container_of(cb, struct fence_array_cb, cb);
+	struct fence_array *array = array_cb->array;
+
+	if (atomic_dec_and_test(&array->num_pending))
+		fence_signal(&array->base);
+}
+
+static bool fence_array_enable_signaling(struct fence *fence)
+{
+	struct fence_array *array = to_fence_array(fence);
+	struct fence_array_cb *cb = (void *)(&array[1]);
+	unsigned i;
+
+	for (i = 0; i < array->num_fences; ++i) {
+		cb[i].array = array;
+		if (fence_add_callback(array->fences[i], &cb[i].cb,
+				       fence_array_cb_func))
+			if (atomic_dec_and_test(&array->num_pending))
+				return false;
+	}
+
+	return true;
+}
+
+static bool fence_array_signaled(struct fence *fence)
+{
+	struct fence_array *array = to_fence_array(fence);
+
+	return atomic_read(&array->num_pending) == 0;
+}
+
+static void fence_array_release(struct fence *fence)
+{
+	struct fence_array *array = to_fence_array(fence);
+	unsigned i;
+
+	for (i = 0; i < array->num_fences; ++i)
+		fence_put(array->fences[i]);
+
+	kfree(array->fences);
+	fence_free(fence);
+}
+
+const struct fence_ops fence_array_ops = {
+	.get_driver_name = fence_array_get_driver_name,
+	.get_timeline_name = fence_array_get_timeline_name,
+	.enable_signaling = fence_array_enable_signaling,
+	.signaled = fence_array_signaled,
+	.wait = fence_default_wait,
+	.release = fence_array_release,
+};
+
+/**
+ * fence_array_create - Create a custom fence array
+ * @num_fences:	[in]	number of fences to add in the array
+ * @fences:	[in]	array containing the fences
+ * @context:	[in]	fence context to use
+ * @seqno:	[in]	sequence number to use
+ *
+ * Allocate a fence_array object and initialize the base fence with fence_init().
+ * In case of error it returns NULL.
+ *
+ * The caller should allocte the fences array with num_fences size
+ * and fill it with the fences it wants to add to the object. Ownership of this
+ * array is take and fence_put() is used on each fence on release.
+ */
+struct fence_array *fence_array_create(int num_fences, struct fence **fences,
+				       u64 context, unsigned seqno)
+{
+	struct fence_array *array;
+	size_t size = sizeof(*array);
+
+	/* Allocate the callback structures behind the array. */
+	size += num_fences * sizeof(struct fence_array_cb);
+	array = kzalloc(size, GFP_KERNEL);
+	if (!array)
+		return NULL;
+
+	spin_lock_init(&array->lock);
+	fence_init(&array->base, &fence_array_ops, &array->lock,
+		   context, seqno);
+
+	array->num_fences = num_fences;
+	atomic_set(&array->num_pending, num_fences);
+	array->fences = fences;
+
+	return array;
+}
+EXPORT_SYMBOL(fence_array_create);

include/linux/fence-array.h

@@ -0,0 +1,72 @@
+/*
+ * fence-array: aggregates fence to be waited together
+ *
+ * Copyright (C) 2016 Collabora Ltd
+ * Copyright (C) 2016 Advanced Micro Devices, Inc.
+ * Authors:
+ *	Gustavo Padovan <gustavo@padovan.org>
+ *	Christian König <christian.koenig@amd.com>
+ *
+ * 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_ARRAY_H
+#define __LINUX_FENCE_ARRAY_H
+
+#include <linux/fence.h>
+
+/**
+ * struct fence_array_cb - callback helper for fence array
+ * @cb: fence callback structure for signaling
+ * @array: reference to the parent fence array object
+ */
+struct fence_array_cb {
+	struct fence_cb cb;
+	struct fence_array *array;
+};
+
+/**
+ * struct fence_array - fence to represent an array of fences
+ * @base: fence base class
+ * @lock: spinlock for fence handling
+ * @num_fences: number of fences in the array
+ * @num_pending: fences in the array still pending
+ * @fences: array of the fences
+ */
+struct fence_array {
+	struct fence base;
+
+	spinlock_t lock;
+	unsigned num_fences;
+	atomic_t num_pending;
+	struct fence **fences;
+};
+
+extern const struct fence_ops fence_array_ops;
+
+/**
+ * to_fence_array - cast a fence to a fence_array
+ * @fence: fence to cast to a fence_array
+ *
+ * Returns NULL if the fence is not a fence_array,
+ * or the fence_array otherwise.
+ */
+static inline struct fence_array *to_fence_array(struct fence *fence)
+{
+	if (fence->ops != &fence_array_ops)
+		return NULL;
+
+	return container_of(fence, struct fence_array, base);
+}
+
+struct fence_array *fence_array_create(int num_fences, struct fence **fences,
+				       u64 context, unsigned seqno);
+
+#endif /* __LINUX_FENCE_ARRAY_H */