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 /* SPDX-License-Identifier: GPL-2.0-only */
 /*
  * 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>
  */
 
 #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 {
     spinlock_t *lock;
     const struct dma_fence_ops *ops;
     /*
      * We clear the callback list on kref_put so that by the time we
      * release the fence it is unused. No one should be adding to the
      * cb_list that they don't themselves hold a reference for.
      *
      * The lifetime of the timestamp is similarly tied to both the
      * rcu freelist and the cb_list. The timestamp is only set upon
      * signaling while simultaneously notifying the cb_list. Ergo, we
      * only use either the cb_list of timestamp. Upon destruction,
      * neither are accessible, and so we can use the rcu. This means
      * that the cb_list is *only* valid until the signal bit is set,
      * and to read either you *must* hold a reference to the fence,
      * and not just the rcu_read_lock.
      *
      * Listed in chronological order.
      */
     union {
         struct list_head cb_list;
         /* @cb_list replaced by @timestamp on dma_fence_signal() */
         ktime_t timestamp;
         /* @timestamp replaced by @rcu on dma_fence_release() */
         struct rcu_head rcu;
     };
     u64 context;
     u64 seqno;
     unsigned long flags;
     struct kref refcount;
     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
  *
  */
 struct dma_fence_ops {
     /**
      * @use_64bit_seqno:
      *
      * True if this dma_fence implementation uses 64bit seqno, false
      * otherwise.
      */
     bool use_64bit_seqno;
 
     /**
      * @get_driver_name:
      *
      * Returns the driver name. This is a callback to allow drivers to
      * compute the name at runtime, without having it to store permanently
      * for each fence, or build a cache of some sort.
      *
      * This callback is mandatory.
      */
     const char * (*get_driver_name)(struct dma_fence *fence);
 
     /**
      * @get_timeline_name:
      *
      * Return the name of the context this fence belongs to. This is a
      * callback to allow drivers to compute the name at runtime, without
      * having it to store permanently for each fence, or build a cache of
      * some sort.
      *
      * This callback is mandatory.
      */
     const char * (*get_timeline_name)(struct dma_fence *fence);
 
     /**
      * @enable_signaling:
      *
      * Enable software signaling of fence.
      *
      * For fence implementations that have the capability for hw->hw
      * signaling, they can implement this op to enable the necessary
      * interrupts, or insert commands into cmdstream, etc, to avoid these
      * costly operations for the common case where only hw->hw
      * synchronization is required.  This is called in the first
      * dma_fence_wait() or dma_fence_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 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.
      *
      * &dma_fence.error may be set in enable_signaling, but only when false
      * is returned.
      *
      * Since many implementations can call dma_fence_signal() even when before
      * @enable_signaling has been called there's a race window, where the
      * dma_fence_signal() might result in the final fence reference being
      * released and its memory freed. To avoid this, implementations of this
      * callback should grab their own reference using dma_fence_get(), to be
      * released when the fence is signalled (through e.g. the interrupt
      * handler).
      *
      * This callback is optional. If this callback is not present, then the
      * driver must always have signaling enabled.
      */
     bool (*enable_signaling)(struct dma_fence *fence);
 
     /**
      * @signaled:
      *
      * Peek whether the fence is signaled, as a fastpath optimization for
      * e.g. dma_fence_wait() or dma_fence_add_callback(). Note that this
      * callback does not need to make any guarantees beyond that a fence
      * once indicates as signalled must always return true from this
      * callback. This callback may return false even if the fence has
      * completed already, in this case information hasn't propogated throug
      * the system yet. See also dma_fence_is_signaled().
      *
      * May set &dma_fence.error if returning true.
      *
      * This callback is optional.
      */
     bool (*signaled)(struct dma_fence *fence);
 
     /**
      * @wait:
      *
      * Custom wait implementation, defaults to dma_fence_default_wait() if
      * not set.
      *
      * Deprecated and should not be used by new implementations. Only used
      * by existing implementations which need special handling for their
      * hardware reset procedure.
      *
      * 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.
      */
     signed long (*wait)(struct dma_fence *fence,
                 bool intr, signed long timeout);
 
     /**
      * @release:
      *
      * Called on destruction of fence to release additional resources.
      * Can be called from irq context.  This callback is optional. If it is
      * NULL, then dma_fence_free() is instead called as the default
      * implementation.
      */
     void (*release)(struct dma_fence *fence);
 
     /**
      * @fence_value_str:
      *
      * Callback to fill in free-form debug info specific to this fence, like
      * the sequence number.
      *
      * This callback is optional.
      */
     void (*fence_value_str)(struct dma_fence *fence, char *str, int size);
 
     /**
      * @timeline_value_str:
      *
      * Fills in the current value of the timeline as a string, like the
      * sequence number. Note that the specific fence passed to this function
      * should not matter, drivers should only use it to look up the
      * corresponding timeline structures.
      */
     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, u64 seqno);
 
 void dma_fence_release(struct kref *kref);
 void dma_fence_free(struct dma_fence *fence);
 void dma_fence_describe(struct dma_fence *fence, struct seq_file *seq);
 
 /**
  * dma_fence_put - decreases refcount of the fence
  * @fence: 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: 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 dma_resv_list with
  *                     rcu read lock
  * @fence: 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: 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 dma_resv. 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)
             return NULL;
 
         if (!dma_fence_get_rcu(fence))
             continue;
 
         /* 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);
 }
 
 #ifdef CONFIG_LOCKDEP
 bool dma_fence_begin_signalling(void);
 void dma_fence_end_signalling(bool cookie);
 void __dma_fence_might_wait(void);
 #else
 static inline bool dma_fence_begin_signalling(void)
 {
     return true;
 }
 static inline void dma_fence_end_signalling(bool cookie) {}
 static inline void __dma_fence_might_wait(void) {}
 #endif
 
 int dma_fence_signal(struct dma_fence *fence);
 int dma_fence_signal_locked(struct dma_fence *fence);
 int dma_fence_signal_timestamp(struct dma_fence *fence, ktime_t timestamp);
 int dma_fence_signal_timestamp_locked(struct dma_fence *fence,
                       ktime_t timestamp);
 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: 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 &dma_fence.lock to be held.
  *
  * See also dma_fence_is_signaled().
  */
 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: 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.
  *
  * See also dma_fence_is_signaled_locked().
  */
 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: the first fence's seqno
  * @f2: the second fence's seqno from the same context
  * @ops: dma_fence_ops associated with the seqno
  *
  * 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(u64 f1, u64 f2,
                     const struct dma_fence_ops *ops)
 {
     /* This is for backward compatibility with drivers which can only handle
      * 32bit sequence numbers. Use a 64bit compare when the driver says to
      * do so.
      */
     if (ops->use_64bit_seqno)
         return f1 > f2;
 
     return (int)(lower_32_bits(f1) - lower_32_bits(f2)) > 0;
 }
 
 /**
  * dma_fence_is_later - return if f1 is chronologically later than f2
  * @f1: the first fence from the same context
  * @f2: 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, f1->ops);
 }
 
 /**
  * dma_fence_later - return the chronologically later fence
  * @f1: the first fence from the same context
  * @f2: 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: 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: the dma_fence
  * @error: 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: the fence to wait on
  * @intr: 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.
  *
  * See also dma_fence_wait_timeout() and dma_fence_wait_any_timeout().
  */
 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;
 }
 
 struct dma_fence *dma_fence_get_stub(void);
 struct dma_fence *dma_fence_allocate_private_stub(void);
 u64 dma_fence_context_alloc(unsigned num);
 
 extern const struct dma_fence_ops dma_fence_array_ops;
 extern const struct dma_fence_ops dma_fence_chain_ops;
 
 /**
  * dma_fence_is_array - check if a fence is from the array subclass
  * @fence: the fence to test
  *
  * Return true if it is a dma_fence_array and false otherwise.
  */
 static inline bool dma_fence_is_array(struct dma_fence *fence)
 {
     return fence->ops == &dma_fence_array_ops;
 }
 
 /**
  * dma_fence_is_chain - check if a fence is from the chain subclass
  * @fence: the fence to test
  *
  * Return true if it is a dma_fence_chain and false otherwise.
  */
 static inline bool dma_fence_is_chain(struct dma_fence *fence)
 {
     return fence->ops == &dma_fence_chain_ops;
 }
 
 /**
  * dma_fence_is_container - check if a fence is a container for other fences
  * @fence: the fence to test
  *
  * Return true if this fence is a container for other fences, false otherwise.
  * This is important since we can't build up large fence structure or otherwise
  * we run into recursion during operation on those fences.
  */
 static inline bool dma_fence_is_container(struct dma_fence *fence)
 {
     return dma_fence_is_array(fence) || dma_fence_is_chain(fence);
 }
 
 #endif /* __LINUX_DMA_FENCE_H */

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