Commit 7bf60c52 authored by Christian König's avatar Christian König Committed by Christian König
Browse files

dma-buf: add new dma_fence_chain container v7 



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.
v3: use head and iterator for dma_fence_chain_for_each
v4: fix reference count in dma_fence_chain_enable_signaling
v5: fix iteration when walking each chain node
v6: add __rcu for member 'prev' of struct chain node
v7: fix rcu warnings from kernel robot

Signed-off-by: default avatarChristian König <christian.koenig@amd.com>
Reviewed-by: default avatarLionel Landwerlin <lionel.g.landwerlin@intel.com>
Link: https://patchwork.freedesktop.org/patch/295778/?series=58813&rev=1
parent 64e1f830

drivers/dma-buf/Makefile

+2 −1
Original line number Diff line number Diff line 
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

drivers/dma-buf/dma-fence-chain.c

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Original line number Diff line number Diff line 
/*

 * fence-chain: chain fences together in a timeline

 *

 * Copyright (C) 2018 Advanced Micro Devices, Inc.

 * Authors:

 *	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/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((void **)&chain->prev, (void *)prev, (void *)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, &chain->base) {

		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);

	dma_fence_put(&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_get(&head->base);

	dma_fence_chain_for_each(fence, &head->base) {

		struct dma_fence_chain *chain = to_dma_fence_chain(fence);

		struct dma_fence *f = chain ? chain->fence : fence;



		dma_fence_get(f);

		if (!dma_fence_add_callback(f, &head->cb, dma_fence_chain_cb)) {

			dma_fence_put(fence);

			return true;

		}

		dma_fence_put(f);

	}

	dma_fence_put(&head->base);

	return false;

}



static bool dma_fence_chain_signaled(struct dma_fence *fence)

{

	dma_fence_chain_for_each(fence, 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(rcu_dereference_protected(chain->prev, true));

	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);

	rcu_assign_pointer(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 && __dma_fence_is_later(seqno, prev->seqno)) {

		context = prev->context;

		chain->prev_seqno = prev->seqno;

	} else {

		context = dma_fence_context_alloc(1);

		/* Make sure that we always have a valid sequence number. */

		if (prev_chain)

			seqno = max(prev->seqno, seqno);

	}



	dma_fence_init(&chain->base, &dma_fence_chain_ops,

		       &chain->lock, context, seqno);

}

EXPORT_SYMBOL(dma_fence_chain_init);

include/linux/dma-fence-chain.h

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Original line number Diff line number Diff line 
/*

 * fence-chain: chain fences together in a timeline

 *

 * Copyright (C) 2018 Advanced Micro Devices, Inc.

 * Authors:

 *	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_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

 * @prev_seqno: original previous seqno before garbage collection

 * @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 __rcu *prev;

	u64 prev_seqno;

	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 || fence->ops != &dma_fence_chain_ops)

		return NULL;



	return container_of(fence, struct dma_fence_chain, base);

}



/**

 * dma_fence_chain_for_each - iterate over all fences in chain

 * @iter: current fence

 * @head: starting point

 *

 * Iterate over all fences in the chain. We keep a reference to the current

 * fence while inside the loop which must be dropped when breaking out.

 */

#define dma_fence_chain_for_each(iter, head)	\

	for (iter = dma_fence_get(head); iter; \

	     iter = dma_fence_chain_walk(iter))



struct dma_fence *dma_fence_chain_walk(struct dma_fence *fence);

int dma_fence_chain_find_seqno(struct dma_fence **pfence, uint64_t seqno);

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 */

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