text: /*
   * 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_FENCE_H
  #define __LINUX_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 fence;
  struct fence_ops;
  struct fence_cb;
  
  /**
   * struct fence - software synchronization primitive
   * @refcount: refcount for this fence
   * @ops: 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
   *           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 FENCE_FLAG_* defined below
   * @timestamp: Timestamp when the fence was signaled.
   * @status: Optional, only valid if < 0, must be set before calling
   * 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.
   *
   * FENCE_FLAG_SIGNALED_BIT - fence is already signaled
   * FENCE_FLAG_ENABLE_SIGNAL_BIT - enable_signaling might have been called*
   * 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 fence_signal was called right
   * before this bit was set, it would have been able to set the
   * FENCE_FLAG_SIGNALED_BIT, before enable_signaling was called.
   * Adding a check for FENCE_FLAG_SIGNALED_BIT after setting
   * FENCE_FLAG_ENABLE_SIGNAL_BIT closes this race, and makes sure that
   * after fence_signal was called, any enable_signaling call will have either
   * been completed, or never called at all.
   */
  struct fence {
  	struct kref refcount;
  	const struct fence_ops *ops;
  	struct rcu_head rcu;
  	struct list_head cb_list;
  	spinlock_t *lock;
  	unsigned context, seqno;
  	unsigned long flags;
  	ktime_t timestamp;
  	int status;
  };
  
  enum fence_flag_bits {
  	FENCE_FLAG_SIGNALED_BIT,
  	FENCE_FLAG_ENABLE_SIGNAL_BIT,
  	FENCE_FLAG_USER_BITS, /* must always be last member */
  };
  
  typedef void (*fence_func_t)(struct fence *fence, struct fence_cb *cb);
  
  /**
   * struct fence_cb - callback for fence_add_callback
   * @node: used by fence_add_callback to append this struct to fence::cb_list
   * @func: fence_func_t to call
   *
   * This struct will be initialized by fence_add_callback, additional
   * data can be passed along by embedding fence_cb in another struct.
   */
  struct fence_cb {
  	struct list_head node;
  	fence_func_t func;
  };
  
  /**
   * struct 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 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 occured that made it impossible to enable
   * signaling. True indicates succesful enabling.
   *
   * fence->status may be set in enable_signaling, but only when false is
   * returned.
   *
   * Calling fence_signal before enable_signaling is called allows
   * for a tiny race window in which enable_signaling is called during,
   * before, or after 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 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 fence_default_wait for default implementation.
   * the 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 fence_ops {
  	const char * (*get_driver_name)(struct fence *fence);
  	const char * (*get_timeline_name)(struct fence *fence);
  	bool (*enable_signaling)(struct fence *fence);
  	bool (*signaled)(struct fence *fence);
  	signed long (*wait)(struct fence *fence, bool intr, signed long timeout);
  	void (*release)(struct fence *fence);
  
  	int (*fill_driver_data)(struct fence *fence, void *data, int size);
  	void (*fence_value_str)(struct fence *fence, char *str, int size);
  	void (*timeline_value_str)(struct fence *fence, char *str, int size);
  };
  
  void fence_init(struct fence *fence, const struct fence_ops *ops,
  		spinlock_t *lock, unsigned context, unsigned seqno);
  
  void fence_release(struct kref *kref);
  void fence_free(struct fence *fence);
  
  /**
   * 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 fence *fence_get(struct fence *fence)
  {
  	if (fence)
  		kref_get(&fence->refcount);
  	return fence;
  }
  
  /**
   * 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 fence *fence_get_rcu(struct fence *fence)
  {
  	if (kref_get_unless_zero(&fence->refcount))
  		return fence;
  	else
  		return NULL;
  }
  
  /**
   * fence_put - decreases refcount of the fence
   * @fence:	[in]	fence to reduce refcount of
   */
  static inline void fence_put(struct fence *fence)
  {
  	if (fence)
  		kref_put(&fence->refcount, fence_release);
  }
  
  int fence_signal(struct fence *fence);
  int fence_signal_locked(struct fence *fence);
  signed long fence_default_wait(struct fence *fence, bool intr, signed long timeout);
  int fence_add_callback(struct fence *fence, struct fence_cb *cb,
  		       fence_func_t func);
  bool fence_remove_callback(struct fence *fence, struct fence_cb *cb);
  void fence_enable_sw_signaling(struct fence *fence);
  
  /**
   * 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 fence_add_callback, fence_wait or fence_enable_sw_signaling
   * haven't been called before.
   *
   * This function requires fence->lock to be held.
   */
  static inline bool
  fence_is_signaled_locked(struct fence *fence)
  {
  	if (test_bit(FENCE_FLAG_SIGNALED_BIT, &fence->flags))
  		return true;
  
  	if (fence->ops->signaled && fence->ops->signaled(fence)) {
  		fence_signal_locked(fence);
  		return true;
  	}
  
  	return false;
  }
  
  /**
   * 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 fence_add_callback, fence_wait or fence_enable_sw_signaling
   * haven't been called before.
   *
   * It's recommended for seqno fences to call 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
  fence_is_signaled(struct fence *fence)
  {
  	if (test_bit(FENCE_FLAG_SIGNALED_BIT, &fence->flags))
  		return true;
  
  	if (fence->ops->signaled && fence->ops->signaled(fence)) {
  		fence_signal(fence);
  		return true;
  	}
  
  	return false;
  }
  
  /**
   * 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 fence *fence_later(struct fence *f1, struct fence *f2)
  {
  	if (WARN_ON(f1->context != f2->context))
  		return NULL;
  
  	/*
  	 * can't check just FENCE_FLAG_SIGNALED_BIT here, it may never have been
  	 * set if enable_signaling wasn't called, and enabling that here is
  	 * overkill.
  	 */
  	if (f2->seqno - f1->seqno <= INT_MAX)
  		return fence_is_signaled(f2) ? NULL : f2;
  	else
  		return fence_is_signaled(f1) ? NULL : f1;
  }
  
  signed long fence_wait_timeout(struct fence *, bool intr, signed long timeout);
  
  
  /**
   * 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 fence_wait(struct fence *fence, bool intr)
  {
  	signed long ret;
  
  	/* Since fence_wait_timeout cannot timeout with
  	 * MAX_SCHEDULE_TIMEOUT, only valid return values are
  	 * -ERESTARTSYS and MAX_SCHEDULE_TIMEOUT.
  	 */
  	ret = fence_wait_timeout(fence, intr, MAX_SCHEDULE_TIMEOUT);
  
  	return ret < 0 ? ret : 0;
  }
  
  unsigned fence_context_alloc(unsigned num);
  
  #define FENCE_TRACE(f, fmt, args...) \
  	do {								\
  		struct fence *__ff = (f);				\
  		if (config_enabled(CONFIG_FENCE_TRACE))			\
  			pr_info("f %u#%u: " fmt,			\
  				__ff->context, __ff->seqno, ##args);	\
  	} while (0)
  
  #define FENCE_WARN(f, fmt, args...) \
  	do {								\
  		struct fence *__ff = (f);				\
  		pr_warn("f %u#%u: " fmt, __ff->context, __ff->seqno,	\
  			 ##args);					\
  	} while (0)
  
  #define FENCE_ERR(f, fmt, args...) \
  	do {								\
  		struct fence *__ff = (f);				\
  		pr_err("f %u#%u: " fmt, __ff->context, __ff->seqno,	\
  			##args);					\
  	} while (0)
  
  #endif /* __LINUX_FENCE_H */
  