include/linux/dma-fence.h - arm/linux - Git at Google

 /*
  * 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.
  * @error: 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_TIMESTAMP_BIT - timestamp recorded for fence signaling
  * 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 error;
 };

 enum dma_fence_flag_bits {
 	DMA_FENCE_FLAG_SIGNALED_BIT,
 	DMA_FENCE_FLAG_TIMESTAMP_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->error 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->error 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
  * @fencep:	[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_TYPESAFE_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_TYPESAFE_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's seqno
  * @f2:	[in]	the second fence's seqno 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 common across contexts.
  */
 static inline bool __dma_fence_is_later(u32 f1, u32 f2)
 {
 	return (int)(f1 - f2) > 0;
 }

 /**
  * 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 __dma_fence_is_later(f1->seqno, f2->seqno);
 }

 /**
  * 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;
 }

 /**
  * dma_fence_get_status_locked - returns the status upon completion
  * @fence: [in]	the dma_fence to query
  *
  * Drivers can supply an optional error status condition before they signal
  * the fence (to indicate whether the fence was completed due to an error
  * rather than success). The value of the status condition is only valid
  * if the fence has been signaled, dma_fence_get_status_locked() first checks
  * the signal state before reporting the error status.
  *
  * Returns 0 if the fence has not yet been signaled, 1 if the fence has
  * been signaled without an error condition, or a negative error code
  * if the fence has been completed in err.
  */
 static inline int dma_fence_get_status_locked(struct dma_fence *fence)
 {
 	if (dma_fence_is_signaled_locked(fence))
 		return fence->error ?: 1;
 	else
 		return 0;
 }

 int dma_fence_get_status(struct dma_fence *fence);

 /**
  * dma_fence_set_error - flag an error condition on the fence
  * @fence: [in]	the dma_fence
  * @error: [in]	the error to store
  *
  * Drivers can supply an optional error status condition before they signal
  * the fence, to indicate that the fence was completed due to an error
  * rather than success. This must be set before signaling (so that the value
  * is visible before any waiters on the signal callback are woken). This
  * helper exists to help catching erroneous setting of #dma_fence.error.
  */
 static inline void dma_fence_set_error(struct dma_fence *fence,
 				       int error)
 {
 	WARN_ON(test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags));
 	WARN_ON(error >= 0 || error < -MAX_ERRNO);

 	fence->error = error;
 }

 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 */
	/*
	* 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.
	* @error: 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_TIMESTAMP_BIT - timestamp recorded for fence signaling
	* 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 error;
	};

	enum dma_fence_flag_bits {
	DMA_FENCE_FLAG_SIGNALED_BIT,
	DMA_FENCE_FLAG_TIMESTAMP_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->error 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->error 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
	* @fencep: [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_TYPESAFE_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_TYPESAFE_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's seqno
	* @f2: [in] the second fence's seqno 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 common across contexts.
	*/
	static inline bool __dma_fence_is_later(u32 f1, u32 f2)
	{
	return (int)(f1 - f2) > 0;
	}

	/**
	* 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 __dma_fence_is_later(f1->seqno, f2->seqno);
	}

	/**
	* 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;
	}

	/**
	* dma_fence_get_status_locked - returns the status upon completion
	* @fence: [in] the dma_fence to query
	*
	* Drivers can supply an optional error status condition before they signal
	* the fence (to indicate whether the fence was completed due to an error
	* rather than success). The value of the status condition is only valid
	* if the fence has been signaled, dma_fence_get_status_locked() first checks
	* the signal state before reporting the error status.
	*
	* Returns 0 if the fence has not yet been signaled, 1 if the fence has
	* been signaled without an error condition, or a negative error code
	* if the fence has been completed in err.
	*/
	static inline int dma_fence_get_status_locked(struct dma_fence *fence)
	{
	if (dma_fence_is_signaled_locked(fence))
	return fence->error ?: 1;
	else
	return 0;
	}

	int dma_fence_get_status(struct dma_fence *fence);

	/**
	* dma_fence_set_error - flag an error condition on the fence
	* @fence: [in] the dma_fence
	* @error: [in] the error to store
	*
	* Drivers can supply an optional error status condition before they signal
	* the fence, to indicate that the fence was completed due to an error
	* rather than success. This must be set before signaling (so that the value
	* is visible before any waiters on the signal callback are woken). This
	* helper exists to help catching erroneous setting of #dma_fence.error.
	*/
	static inline void dma_fence_set_error(struct dma_fence *fence,
	int error)
	{
	WARN_ON(test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags));
	WARN_ON(error >= 0 \|\| error < -MAX_ERRNO);

	fence->error = error;
	}

	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 */