/*
   * 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 */