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/* SPDX-License-Identifier: GPL-2.0-only */
* seqno-fence, using a dma-buf to synchronize fencing
* Copyright (C) 2012 Texas Instruments
* Copyright (C) 2012 Canonical Ltd
* Authors:
* Rob Clark <>
* Maarten Lankhorst <>
#include <linux/dma-fence.h>
#include <linux/dma-buf.h>
enum seqno_fence_condition {
struct seqno_fence {
struct dma_fence base;
const struct dma_fence_ops *ops;
struct dma_buf *sync_buf;
uint32_t seqno_ofs;
enum seqno_fence_condition condition;
extern const struct dma_fence_ops seqno_fence_ops;
* to_seqno_fence - cast a fence to a seqno_fence
* @fence: fence to cast to a seqno_fence
* Returns NULL if the fence is not a seqno_fence,
* or the seqno_fence otherwise.
static inline struct seqno_fence *
to_seqno_fence(struct dma_fence *fence)
if (fence->ops != &seqno_fence_ops)
return NULL;
return container_of(fence, struct seqno_fence, base);
* seqno_fence_init - initialize a seqno fence
* @fence: seqno_fence to initialize
* @lock: pointer to spinlock to use for fence
* @sync_buf: buffer containing the memory location to signal on
* @context: the execution context this fence is a part of
* @seqno_ofs: the offset within @sync_buf
* @seqno: the sequence # to signal on
* @cond: fence wait condition
* @ops: the fence_ops for operations on this seqno fence
* This function initializes a struct seqno_fence with passed parameters,
* and takes a reference on sync_buf which is released on fence destruction.
* A seqno_fence is a dma_fence which can complete in software when
* enable_signaling is called, but it also completes when
* (s32)((sync_buf)[seqno_ofs] - seqno) >= 0 is true
* The seqno_fence will take a refcount on the sync_buf until it's
* destroyed, but actual lifetime of sync_buf may be longer if one of the
* callers take a reference to it.
* Certain hardware have instructions to insert this type of wait condition
* in the command stream, so no intervention from software would be needed.
* This type of fence can be destroyed before completed, however a reference
* on the sync_buf dma-buf can be taken. It is encouraged to re-use the same
* dma-buf for sync_buf, since mapping or unmapping the sync_buf to the
* device's vm can be expensive.
* It is recommended for creators of seqno_fence to call dma_fence_signal()
* before destruction. This will prevent possible issues from wraparound at
* time of issue vs time of check, since users can check dma_fence_is_signaled()
* before submitting instructions for the hardware to wait on the fence.
* However, when ops.enable_signaling is not called, it doesn't have to be
* done as soon as possible, just before there's any real danger of seqno
* wraparound.
static inline void
seqno_fence_init(struct seqno_fence *fence, spinlock_t *lock,
struct dma_buf *sync_buf, uint32_t context,
uint32_t seqno_ofs, uint32_t seqno,
enum seqno_fence_condition cond,
const struct dma_fence_ops *ops)
BUG_ON(!fence || !sync_buf || !ops);
BUG_ON(!ops->wait || !ops->enable_signaling ||
!ops->get_driver_name || !ops->get_timeline_name);
* ops is used in dma_fence_init for get_driver_name, so needs to be
* initialized first
fence->ops = ops;
dma_fence_init(&fence->base, &seqno_fence_ops, lock, context, seqno);
fence->sync_buf = sync_buf;
fence->seqno_ofs = seqno_ofs;
fence->condition = cond;
#endif /* __LINUX_SEQNO_FENCE_H */