/*
 * 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_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_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 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;
}

/**
 * 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)
{
        BUG_ON(test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags));
        BUG_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 */