/*
* Fence mechanism for dma-buf to allow for asynchronous dma access
*
* Copyright (C) 2012 Canonical Ltd
* Copyright (C) 2012 Texas Instruments
*
* Authors:
* Rob Clark <robdclark@gmail.com>
* Maarten Lankhorst <maarten.lankhorst@canonical.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_H
#define __LINUX_DMA_FENCE_H
#include <linux/err.h>
#include <linux/wait.h>
#include <linux/list.h>
#include <linux/bitops.h>
#include <linux/kref.h>
#include <linux/sched.h>
#include <linux/printk.h>
#include <linux/rcupdate.h>
struct dma_fence;
struct dma_fence_ops;
struct dma_fence_cb;
/**
* struct dma_fence - software synchronization primitive
* @refcount: refcount for this fence
* @ops: dma_fence_ops associated with this fence
* @rcu: used for releasing fence with kfree_rcu
* @cb_list: list of all callbacks to call
* @lock: spin_lock_irqsave used for locking
* @context: execution context this fence belongs to, returned by
* dma_fence_context_alloc()
* @seqno: the sequence number of this fence inside the execution context,
* can be compared to decide which fence would be signaled later.
* @flags: A mask of DMA_FENCE_FLAG_* defined below
* @timestamp: Timestamp when the fence was signaled.
* @status: Optional, only valid if < 0, must be set before calling
* dma_fence_signal, indicates that the fence has completed with an error.
*
* the flags member must be manipulated and read using the appropriate
* atomic ops (bit_*), so taking the spinlock will not be needed most
* of the time.
*
* DMA_FENCE_FLAG_SIGNALED_BIT - fence is already signaled
* DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT - enable_signaling might have been called
* DMA_FENCE_FLAG_USER_BITS - start of the unused bits, can be used by the
* implementer of the fence for its own purposes. Can be used in different
* ways by different fence implementers, so do not rely on this.
*
* Since atomic bitops are used, this is not guaranteed to be the case.
* Particularly, if the bit was set, but dma_fence_signal was called right
* before this bit was set, it would have been able to set the
* DMA_FENCE_FLAG_SIGNALED_BIT, before enable_signaling was called.
* Adding a check for DMA_FENCE_FLAG_SIGNALED_BIT after setting
* DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT closes this race, and makes sure that
* after dma_fence_signal was called, any enable_signaling call will have either
* been completed, or never called at all.
*/
struct dma_fence {
struct kref refcount;
const struct dma_fence_ops *ops;
struct rcu_head rcu;
struct list_head cb_list;
spinlock_t *lock;
u64 context;
unsigned seqno;
unsigned long flags;
ktime_t timestamp;
int status;
};
enum dma_fence_flag_bits {
DMA_FENCE_FLAG_SIGNALED_BIT,
DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT,
DMA_FENCE_FLAG_USER_BITS, /* must always be last member */
};
typedef void (*dma_fence_func_t)(struct dma_fence *fence,
struct dma_fence_cb *cb);
/**
* struct dma_fence_cb - callback for dma_fence_add_callback
* @node: used by dma_fence_add_callback to append this struct to fence::cb_list
* @func: dma_fence_func_t to call
*
* This struct will be initialized by dma_fence_add_callback, additional
* data can be passed along by embedding dma_fence_cb in another struct.
*/
struct dma_fence_cb {
struct list_head node;
dma_fence_func_t func;
};
/**
* struct dma_fence_ops - operations implemented for fence
* @get_driver_name: returns the driver name.
* @get_timeline_name: return the name of the context this fence belongs to.
* @enable_signaling: enable software signaling of fence.
* @signaled: [optional] peek whether the fence is signaled, can be null.
* @wait: custom wait implementation, or dma_fence_default_wait.
* @release: [optional] called on destruction of fence, can be null
* @fill_driver_data: [optional] callback to fill in free-form debug info
* Returns amount of bytes filled, or -errno.
* @fence_value_str: [optional] fills in the value of the fence as a string
* @timeline_value_str: [optional] fills in the current value of the timeline
* as a string
*
* Notes on enable_signaling:
* For fence implementations that have the capability for hw->hw
* signaling, they can implement this op to enable the necessary
* irqs, or insert commands into cmdstream, etc. This is called
* in the first wait() or add_callback() path to let the fence
* implementation know that there is another driver waiting on
* the signal (ie. hw->sw case).
*
* This function can be called called from atomic context, but not
* from irq context, so normal spinlocks can be used.
*
* A return value of false indicates the fence already passed,
* or some failure occurred that made it impossible to enable
* signaling. True indicates successful enabling.
*
* fence->status may be set in enable_signaling, but only when false is
* returned.
*
* Calling dma_fence_signal before enable_signaling is called allows
* for a tiny race window in which enable_signaling is called during,
* before, or after dma_fence_signal. To fight this, it is recommended
* that before enable_signaling returns true an extra reference is
* taken on the fence, to be released when the fence is signaled.
* This will mean dma_fence_signal will still be called twice, but
* the second time will be a noop since it was already signaled.
*
* Notes on signaled:
* May set fence->status if returning true.
*
* Notes on wait:
* Must not be NULL, set to dma_fence_default_wait for default implementation.
* the dma_fence_default_wait implementation should work for any fence, as long
* as enable_signaling works correctly.
*
* Must return -ERESTARTSYS if the wait is intr = true and the wait was
* interrupted, and remaining jiffies if fence has signaled, or 0 if wait
* timed out. Can also return other error values on custom implementations,
* which should be treated as if the fence is signaled. For example a hardware
* lockup could be reported like that.
*
* Notes on release:
* Can be NULL, this function allows additional commands to run on
* destruction of the fence. Can be called from irq context.
* If pointer is set to NULL, kfree will get called instead.
*/
struct dma_fence_ops {
const char * (*get_driver_name)(struct dma_fence *fence);
const char * (*get_timeline_name)(struct dma_fence *fence);
bool (*enable_signaling)(struct dma_fence *fence);
bool (*signaled)(struct dma_fence *fence);
signed long (*wait)(struct dma_fence *fence,
bool intr, signed long timeout);
void (*release)(struct dma_fence *fence);
int (*fill_driver_data)(struct dma_fence *fence, void *data, int size);
void (*fence_value_str)(struct dma_fence *fence, char *str, int size);
void (*timeline_value_str)(struct dma_fence *fence,
char *str, int size);
};
void dma_fence_init(struct dma_fence *fence, const struct dma_fence_ops *ops,
spinlock_t *lock, u64 context, unsigned seqno);
void dma_fence_release(struct kref *kref);
void dma_fence_free(struct dma_fence *fence);
/**
* dma_fence_put - decreases refcount of the fence
* @fence: [in] fence to reduce refcount of
*/
static inline void dma_fence_put(struct dma_fence *fence)
{
if (fence)
kref_put(&fence->refcount, dma_fence_release);
}
/**
* dma_fence_get - increases refcount of the fence
* @fence: [in] fence to increase refcount of
*
* Returns the same fence, with refcount increased by 1.
*/
static inline struct dma_fence *dma_fence_get(struct dma_fence *fence)
{
if (fence)
kref_get(&fence->refcount);
return fence;
}
/**
* dma_fence_get_rcu - get a fence from a reservation_object_list with
* rcu read lock
* @fence: [in] fence to increase refcount of
*
* Function returns NULL if no refcount could be obtained, or the fence.
*/
static inline struct dma_fence *dma_fence_get_rcu(struct dma_fence *fence)
{
if (kref_get_unless_zero(&fence->refcount))
return fence;
else
return NULL;
}
/**
* dma_fence_get_rcu_safe - acquire a reference to an RCU tracked fence
* @fence: [in] pointer to fence to increase refcount of
*
* Function returns NULL if no refcount could be obtained, or the fence.
* This function handles acquiring a reference to a fence that may be
* reallocated within the RCU grace period (such as with SLAB_DESTROY_BY_RCU),
* so long as the caller is using RCU on the pointer to the fence.
*
* An alternative mechanism is to employ a seqlock to protect a bunch of
* fences, such as used by struct reservation_object. When using a seqlock,
* the seqlock must be taken before and checked after a reference to the
* fence is acquired (as shown here).
*
* The caller is required to hold the RCU read lock.
*/
static inline struct dma_fence *
dma_fence_get_rcu_safe(struct dma_fence * __rcu *fencep)
{
do {
struct dma_fence *fence;
fence = rcu_dereference(*fencep);
if (!fence || !dma_fence_get_rcu(fence))
return NULL;
/* The atomic_inc_not_zero() inside dma_fence_get_rcu()
* provides a full memory barrier upon success (such as now).
* This is paired with the write barrier from assigning
* to the __rcu protected fence pointer so that if that
* pointer still matches the current fence, we know we
* have successfully acquire a reference to it. If it no
* longer matches, we are holding a reference to some other
* reallocated pointer. This is possible if the allocator
* is using a freelist like SLAB_DESTROY_BY_RCU where the
* fence remains valid for the RCU grace period, but it
* may be reallocated. When using such allocators, we are
* responsible for ensuring the reference we get is to
* the right fence, as below.
*/
if (fence == rcu_access_pointer(*fencep))
return rcu_pointer_handoff(fence);
dma_fence_put(fence);
} while (1);
}
int dma_fence_signal(struct dma_fence *fence);
int dma_fence_signal_locked(struct dma_fence *fence);
signed long dma_fence_default_wait(struct dma_fence *fence,
bool intr, signed long timeout);
int dma_fence_add_callback(struct dma_fence *fence,
struct dma_fence_cb *cb,
dma_fence_func_t func);
bool dma_fence_remove_callback(struct dma_fence *fence,
struct dma_fence_cb *cb);
void dma_fence_enable_sw_signaling(struct dma_fence *fence);
/**
* dma_fence_is_signaled_locked - Return an indication if the fence
* is signaled yet.
* @fence: [in] the fence to check
*
* Returns true if the fence was already signaled, false if not. Since this
* function doesn't enable signaling, it is not guaranteed to ever return
* true if dma_fence_add_callback, dma_fence_wait or
* dma_fence_enable_sw_signaling haven't been called before.
*
* This function requires fence->lock to be held.
*/
static inline bool
dma_fence_is_signaled_locked(struct dma_fence *fence)
{
if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags))
return true;
if (fence->ops->signaled && fence->ops->signaled(fence)) {
dma_fence_signal_locked(fence);
return true;
}
return false;
}
/**
* dma_fence_is_signaled - Return an indication if the fence is signaled yet.
* @fence: [in] the fence to check
*
* Returns true if the fence was already signaled, false if not. Since this
* function doesn't enable signaling, it is not guaranteed to ever return
* true if dma_fence_add_callback, dma_fence_wait or
* dma_fence_enable_sw_signaling haven't been called before.
*
* It's recommended for seqno fences to call dma_fence_signal when the
* operation is complete, it makes it possible to prevent issues from
* wraparound between time of issue and time of use by checking the return
* value of this function before calling hardware-specific wait instructions.
*/
static inline bool
dma_fence_is_signaled(struct dma_fence *fence)
{
if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags))
return true;
if (fence->ops->signaled && fence->ops->signaled(fence)) {
dma_fence_signal(fence);
return true;
}
return false;
}
/**
* dma_fence_is_later - return if f1 is chronologically later than f2
* @f1: [in] the first fence from the same context
* @f2: [in] the second fence from the same context
*
* Returns true if f1 is chronologically later than f2. Both fences must be
* from the same context, since a seqno is not re-used across contexts.
*/
static inline bool dma_fence_is_later(struct dma_fence *f1,
struct dma_fence *f2)
{
if (WARN_ON(f1->context != f2->context))
return false;
return (int)(f1->seqno - f2->seqno) > 0;
}
/**
* dma_fence_later - return the chronologically later fence
* @f1: [in] the first fence from the same context
* @f2: [in] the second fence from the same context
*
* Returns NULL if both fences are signaled, otherwise the fence that would be
* signaled last. Both fences must be from the same context, since a seqno is
* not re-used across contexts.
*/
static inline struct dma_fence *dma_fence_later(struct dma_fence *f1,
struct dma_fence *f2)
{
if (WARN_ON(f1->context != f2->context))
return NULL;
/*
* Can't check just DMA_FENCE_FLAG_SIGNALED_BIT here, it may never
* have been set if enable_signaling wasn't called, and enabling that
* here is overkill.
*/
if (dma_fence_is_later(f1, f2))
return dma_fence_is_signaled(f1) ? NULL : f1;
else
return dma_fence_is_signaled(f2) ? NULL : f2;
}
signed long dma_fence_wait_timeout(struct dma_fence *,
bool intr, signed long timeout);
signed long dma_fence_wait_any_timeout(struct dma_fence **fences,
uint32_t count,
bool intr, signed long timeout,
uint32_t *idx);
/**
* dma_fence_wait - sleep until the fence gets signaled
* @fence: [in] the fence to wait on
* @intr: [in] if true, do an interruptible wait
*
* This function will return -ERESTARTSYS if interrupted by a signal,
* or 0 if the fence was signaled. Other error values may be
* returned on custom implementations.
*
* Performs a synchronous wait on this fence. It is assumed the caller
* directly or indirectly holds a reference to the fence, otherwise the
* fence might be freed before return, resulting in undefined behavior.
*/
static inline signed long dma_fence_wait(struct dma_fence *fence, bool intr)
{
signed long ret;
/* Since dma_fence_wait_timeout cannot timeout with
* MAX_SCHEDULE_TIMEOUT, only valid return values are
* -ERESTARTSYS and MAX_SCHEDULE_TIMEOUT.
*/
ret = dma_fence_wait_timeout(fence, intr, MAX_SCHEDULE_TIMEOUT);
return ret < 0 ? ret : 0;
}
u64 dma_fence_context_alloc(unsigned num);
#define DMA_FENCE_TRACE(f, fmt, args...) \
do { \
struct dma_fence *__ff = (f); \
if (IS_ENABLED(CONFIG_DMA_FENCE_TRACE)) \
pr_info("f %llu#%u: " fmt, \
__ff->context, __ff->seqno, ##args); \
} while (0)
#define DMA_FENCE_WARN(f, fmt, args...) \
do { \
struct dma_fence *__ff = (f); \
pr_warn("f %llu#%u: " fmt, __ff->context, __ff->seqno, \
##args); \
} while (0)
#define DMA_FENCE_ERR(f, fmt, args...) \
do { \
struct dma_fence *__ff = (f); \
pr_err("f %llu#%u: " fmt, __ff->context, __ff->seqno, \
##args); \
} while (0)
#endif /* __LINUX_DMA_FENCE_H */
