From: Gustavo Padovan <gustavo.pado...@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 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.

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 at collabora.co.uk>
Signed-off-by: Christian König <christian.koenig at amd.com>
---
 drivers/dma-buf/Makefile      |   2 +-
 drivers/dma-buf/fence-array.c | 127 ++++++++++++++++++++++++++++++++++++++++++
 include/linux/fence-array.h   |  72 ++++++++++++++++++++++++
 3 files changed, 200 insertions(+), 1 deletion(-)
 create mode 100644 drivers/dma-buf/fence-array.c
 create mode 100644 include/linux/fence-array.h

diff --git a/drivers/dma-buf/Makefile b/drivers/dma-buf/Makefile
index 57a675f..85f6928 100644
--- a/drivers/dma-buf/Makefile
+++ b/drivers/dma-buf/Makefile
@@ -1 +1 @@
-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
diff --git a/drivers/dma-buf/fence-array.c b/drivers/dma-buf/fence-array.c
new file mode 100644
index 0000000..8141217
--- /dev/null
+++ b/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 at padovan.org>
+ *     Christian König <christian.koenig at 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);
diff --git a/include/linux/fence-array.h b/include/linux/fence-array.h
new file mode 100644
index 0000000..593ab98
--- /dev/null
+++ b/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 at padovan.org>
+ *     Christian König <christian.koenig at 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 */
-- 
2.5.0

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