Lockless container implementation similar to a dma_fence_array, but with
only two elements per node and automatic garbage collection.
v2: properly document dma_fence_chain_for_each, add
dma_fence_chain_find_seqno,
drop prev reference during garbage collection if it's not a
chain fence.
Signed-off-by: Christian König <christian.koenig@xxxxxxx>
---
drivers/dma-buf/Makefile | 3 +-
drivers/dma-buf/dma-fence-chain.c | 235
++++++++++++++++++++++++++++++++++++++
include/linux/dma-fence-chain.h | 79 +++++++++++++
3 files changed, 316 insertions(+), 1 deletion(-)
create mode 100644 drivers/dma-buf/dma-fence-chain.c
create mode 100644 include/linux/dma-fence-chain.h
diff --git a/drivers/dma-buf/Makefile b/drivers/dma-buf/Makefile
index 0913a6ccab5a..1f006e083eb9 100644
--- a/drivers/dma-buf/Makefile
+++ b/drivers/dma-buf/Makefile
@@ -1,4 +1,5 @@
-obj-y := dma-buf.o dma-fence.o dma-fence-array.o reservation.o
seqno-fence.o
+obj-y := dma-buf.o dma-fence.o dma-fence-array.o dma-fence-chain.o \
+ reservation.o seqno-fence.o
obj-$(CONFIG_SYNC_FILE) += sync_file.o
obj-$(CONFIG_SW_SYNC) += sw_sync.o sync_debug.o
obj-$(CONFIG_UDMABUF) += udmabuf.o
diff --git a/drivers/dma-buf/dma-fence-chain.c
b/drivers/dma-buf/dma-fence-chain.c
new file mode 100644
index 000000000000..de05101fc48d
--- /dev/null
+++ b/drivers/dma-buf/dma-fence-chain.c
@@ -0,0 +1,235 @@
+/*
+ * fence-chain: chain fences together in a timeline
+ *
+ * Copyright (C) 2018 Advanced Micro Devices, Inc.
+ * Authors:
+ * Christian König <christian.koenig@xxxxxxx>
+ *
+ * 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/dma-fence-chain.h>
+
+static bool dma_fence_chain_enable_signaling(struct dma_fence *fence);
+
+/**
+ * dma_fence_chain_get_prev - use RCU to get a reference to the
previous fence
+ * @chain: chain node to get the previous node from
+ *
+ * Use dma_fence_get_rcu_safe to get a reference to the previous
fence of the
+ * chain node.
+ */
+static struct dma_fence *dma_fence_chain_get_prev(struct
dma_fence_chain *chain)
+{
+ struct dma_fence *prev;
+
+ rcu_read_lock();
+ prev = dma_fence_get_rcu_safe(&chain->prev);
+ rcu_read_unlock();
+ return prev;
+}
+
+/**
+ * dma_fence_chain_walk - chain walking function
+ * @fence: current chain node
+ *
+ * Walk the chain to the next node. Returns the next fence or NULL
if we are at
+ * the end of the chain. Garbage collects chain nodes which are already
+ * signaled.
+ */
+struct dma_fence *dma_fence_chain_walk(struct dma_fence *fence)
+{
+ struct dma_fence_chain *chain, *prev_chain;
+ struct dma_fence *prev, *replacement, *tmp;
+
+ chain = to_dma_fence_chain(fence);
+ if (!chain) {
+ dma_fence_put(fence);
+ return NULL;
+ }
+
+ while ((prev = dma_fence_chain_get_prev(chain))) {
+
+ prev_chain = to_dma_fence_chain(prev);
+ if (prev_chain) {
+ if (!dma_fence_is_signaled(prev_chain->fence))
+ break;
+
+ replacement = dma_fence_chain_get_prev(prev_chain);
+ } else {
+ if (!dma_fence_is_signaled(prev))
+ break;
+
+ replacement = NULL;
+ }
+
+ tmp = cmpxchg(&chain->prev, prev, replacement);
+ if (tmp == prev)
+ dma_fence_put(tmp);
+ else
+ dma_fence_put(replacement);
+ dma_fence_put(prev);
+ }
+
+ dma_fence_put(fence);
+ return prev;
+}
+EXPORT_SYMBOL(dma_fence_chain_walk);
+
+/**
+ * dma_fence_chain_find_seqno - find fence chain node by seqno
+ * @pfence: pointer to the chain node where to start
+ * @seqno: the sequence number to search for
+ *
+ * Advance the fence pointer to the chain node which will signal
this sequence
+ * number. If no sequence number is provided then this is a no-op.
+ *
+ * Returns EINVAL if the fence is not a chain node or the sequence
number has
+ * not yet advanced far enough.
+ */
+int dma_fence_chain_find_seqno(struct dma_fence **pfence, uint64_t
seqno)
+{
+ struct dma_fence_chain *chain;
+
+ if (!seqno)
+ return 0;
+
+ chain = to_dma_fence_chain(*pfence);
+ if (!chain || chain->base.seqno < seqno)
+ return -EINVAL;
+
+ dma_fence_chain_for_each(*pfence) {
+ if ((*pfence)->context != chain->base.context ||
+ to_dma_fence_chain(*pfence)->prev_seqno < seqno)
+ break;
+ }
+ dma_fence_put(&chain->base);
+
+ return 0;
+}
+EXPORT_SYMBOL(dma_fence_chain_find_seqno);
+
+static const char *dma_fence_chain_get_driver_name(struct dma_fence
*fence)
+{
+ return "dma_fence_chain";
+}
+
+static const char *dma_fence_chain_get_timeline_name(struct
dma_fence *fence)
+{
+ return "unbound";
+}
+
+static void dma_fence_chain_irq_work(struct irq_work *work)
+{
+ struct dma_fence_chain *chain;
+
+ chain = container_of(work, typeof(*chain), work);
+
+ /* Try to rearm the callback */
+ if (!dma_fence_chain_enable_signaling(&chain->base))
+ /* Ok, we are done. No more unsignaled fences left */
+ dma_fence_signal(&chain->base);
+}
+
+static void dma_fence_chain_cb(struct dma_fence *f, struct
dma_fence_cb *cb)
+{
+ struct dma_fence_chain *chain;
+
+ chain = container_of(cb, typeof(*chain), cb);
+ irq_work_queue(&chain->work);
+ dma_fence_put(f);
+}
+
+static bool dma_fence_chain_enable_signaling(struct dma_fence *fence)
+{
+ struct dma_fence_chain *head = to_dma_fence_chain(fence);
+
+ dma_fence_chain_for_each(fence) {
+ struct dma_fence_chain *chain = to_dma_fence_chain(fence);
+ struct dma_fence *f = chain ? chain->fence : fence;
+
+ if (!dma_fence_add_callback(f, &head->cb, dma_fence_chain_cb))
+ return true;
+ }
+ return false;
+}
+
+static bool dma_fence_chain_signaled(struct dma_fence *fence)
+{
+ dma_fence_chain_for_each(fence) {
+ struct dma_fence_chain *chain = to_dma_fence_chain(fence);
+ struct dma_fence *f = chain ? chain->fence : fence;
+
+ if (!dma_fence_is_signaled(f)) {
+ dma_fence_put(fence);
+ return false;
+ }
+ }
+
+ return true;
+}
+
+static void dma_fence_chain_release(struct dma_fence *fence)
+{
+ struct dma_fence_chain *chain = to_dma_fence_chain(fence);
+
+ dma_fence_put(chain->prev);
+ dma_fence_put(chain->fence);
+ dma_fence_free(fence);
+}
+
+const struct dma_fence_ops dma_fence_chain_ops = {
+ .get_driver_name = dma_fence_chain_get_driver_name,
+ .get_timeline_name = dma_fence_chain_get_timeline_name,
+ .enable_signaling = dma_fence_chain_enable_signaling,
+ .signaled = dma_fence_chain_signaled,
+ .release = dma_fence_chain_release,
+};
+EXPORT_SYMBOL(dma_fence_chain_ops);
+
+/**
+ * dma_fence_chain_init - initialize a fence chain
+ * @chain: the chain node to initialize
+ * @prev: the previous fence
+ * @fence: the current fence
+ *
+ * Initialize a new chain node and either start a new chain or add
the node to
+ * the existing chain of the previous fence.
+ */
+void dma_fence_chain_init(struct dma_fence_chain *chain,
+ struct dma_fence *prev,
+ struct dma_fence *fence,
+ uint64_t seqno)
+{
+ struct dma_fence_chain *prev_chain = to_dma_fence_chain(prev);
+ uint64_t context;
+
+ spin_lock_init(&chain->lock);
+ chain->prev = prev;
+ chain->fence = fence;
+ chain->prev_seqno = 0;
+ init_irq_work(&chain->work, dma_fence_chain_irq_work);
+
+ /* Try to reuse the context of the previous chain node. */
+ if (prev_chain && seqno > prev->seqno &&
+ __dma_fence_is_later(seqno, prev->seqno)) {
