> -----Original Message-----
> From: Christian König <ckoenig.leichtzumer...@gmail.com>
> Sent: Thursday, November 15, 2018 7:13 PM
> To: dri-devel@lists.freedesktop.org
> Cc: ch...@chris-wilson.co.uk; daniel.vet...@ffwll.ch; e...@anholt.net; Zhou,
> David(ChunMing) <david1.z...@amd.com>
> Subject: [PATCH 2/7] dma-buf: add new dma_fence_chain container
>
> Lockless container implementation similar to a dma_fence_array, but with
> only two elements per node and automatic garbage collection.
>
> Signed-off-by: Christian König <christian.koe...@amd.com>
> ---
> drivers/dma-buf/Makefile | 3 +-
> drivers/dma-buf/dma-fence-chain.c | 186
> ++++++++++++++++++++++++++++++++++++++
> include/linux/dma-fence-chain.h | 69 ++++++++++++++
> 3 files changed, 257 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..ac830b886589
> --- /dev/null
> +++ b/drivers/dma-buf/dma-fence-chain.c
> @@ -0,0 +1,186 @@
> +/*
> + * fence-chain: chain fences together in a timeline
> + *
> + * Copyright (C) 2018 Advanced Micro Devices, Inc.
> + * Authors:
> + * Christian König <christian.koe...@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/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, *prev_prev, *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 || !dma_fence_is_signaled(prev_chain-
> >fence))
> + break;
> +
> + prev_prev = dma_fence_chain_get_prev(prev_chain);
> + tmp = cmpxchg(&chain->prev, prev, prev_prev);
> + if (tmp == prev)
> + dma_fence_put(tmp);
> + else
> + dma_fence_put(prev_prev);
> + dma_fence_put(prev);
> + }
> +
> + dma_fence_put(fence);
> + return prev;
> +}
> +EXPORT_SYMBOL(dma_fence_chain_walk);
> +
> +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;
Here chain seems never be NULL, so this line can be removed, except that,
dma_fence_chain is fine with me.
-David
> +
> + dma_fence_get(f);
> + if (!dma_fence_add_callback(f, &head->cb,
> dma_fence_chain_cb))
> + return true;
> + dma_fence_put(f);
> + }
> + 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))
> + 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)
> +{
> + uint64_t context;
> +
> + /* Try to reuse the context of the previous chain node. */
> + if (to_dma_fence_chain(prev) &&
> + __dma_fence_is_later(seqno, prev->seqno))
> + context = prev->context;
> + else
> + context = dma_fence_context_alloc(1);
> +
> + spin_lock_init(&chain->lock);
> + dma_fence_init(&chain->base, &dma_fence_chain_ops,
> + &chain->lock, context, seqno);
> + chain->prev = prev;
> + chain->fence = fence;
> + init_irq_work(&chain->work, dma_fence_chain_irq_work); }
> +EXPORT_SYMBOL(dma_fence_chain_init);
> diff --git a/include/linux/dma-fence-chain.h b/include/linux/dma-fence-
> chain.h new file mode 100644 index 000000000000..0e295698fcf8
> --- /dev/null
> +++ b/include/linux/dma-fence-chain.h
> @@ -0,0 +1,69 @@
> +/*
> + * fence-chain: chain fences together in a timeline
> + *
> + * Copyright (C) 2018 Advanced Micro Devices, Inc.
> + * Authors:
> + * Christian König <christian.koe...@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_DMA_FENCE_CHAIN_H
> +#define __LINUX_DMA_FENCE_CHAIN_H
> +
> +#include <linux/dma-fence.h>
> +#include <linux/irq_work.h>
> +
> +/**
> + * struct dma_fence_chain - fence to represent an node of a fence chain
> + * @base: fence base class
> + * @lock: spinlock for fence handling
> + * @prev: previous fence of the chain
> + * @fence: encapsulated fence
> + * @cb: callback structure for signaling
> + * @work: irq work item for signaling
> + */
> +struct dma_fence_chain {
> + struct dma_fence base;
> + spinlock_t lock;
> + struct dma_fence *prev;
> + struct dma_fence *fence;
> + struct dma_fence_cb cb;
> + struct irq_work work;
> +};
> +
> +extern const struct dma_fence_ops dma_fence_chain_ops;
> +
> +/**
> + * to_dma_fence_chain - cast a fence to a dma_fence_chain
> + * @fence: fence to cast to a dma_fence_array
> + *
> + * Returns NULL if the fence is not a dma_fence_chain,
> + * or the dma_fence_chain otherwise.
> + */
> +static inline struct dma_fence_chain *
> +to_dma_fence_chain(struct dma_fence *fence) {
> + if (fence->ops != &dma_fence_chain_ops)
> + return NULL;
> +
> + return container_of(fence, struct dma_fence_chain, base); }
> +
> +#define dma_fence_chain_for_each(fence) \
> + for
> (dma_fence_get(fence);fence;fence=dma_fence_chain_walk(fence))
> +
> +struct dma_fence *dma_fence_chain_walk(struct dma_fence *fence); void
> +dma_fence_chain_init(struct dma_fence_chain *chain,
> + struct dma_fence *prev,
> + struct dma_fence *fence,
> + uint64_t seqno);
> +
> +#endif /* __LINUX_DMA_FENCE_CHAIN_H */
> --
> 2.14.1
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