dma-fence.h

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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>
#include <linux/timekeeping.h>
 
struct dma_fence;
struct dma_fence_ops;
struct dma_fence_cb;
struct seq_file;
 
struct dma_fence {
    union {
        spinlock_t *extern_lock;
        spinlock_t inline_lock;
    };
    const struct dma_fence_ops __rcu *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_INITIALIZED_BIT,
    DMA_FENCE_FLAG_INLINE_LOCK_BIT,
    DMA_FENCE_FLAG_SEQNO64_BIT,
    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 {
    struct list_head node;
    dma_fence_func_t func;
};
 
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);
 
    void (*set_deadline)(struct dma_fence *fence, ktime_t deadline);
};
 
void dma_fence_init(struct dma_fence *fence, const struct dma_fence_ops *ops,
            spinlock_t *lock, u64 context, u64 seqno);
 
void dma_fence_init64(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);
 
static inline bool dma_fence_was_initialized(struct dma_fence *fence)
{
    return fence && test_bit(DMA_FENCE_FLAG_INITIALIZED_BIT, &fence->flags);
}
 
static inline void dma_fence_put(struct dma_fence *fence)
{
    if (fence)
        kref_put(&fence->refcount, dma_fence_release);
}
 
static inline struct dma_fence *dma_fence_get(struct dma_fence *fence)
{
    if (fence)
        kref_get(&fence->refcount);
    return 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;
}
 
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);
}
 
static inline spinlock_t *dma_fence_spinlock(struct dma_fence *fence)
{
    return test_bit(DMA_FENCE_FLAG_INLINE_LOCK_BIT, &fence->flags) ?
        &fence->inline_lock : fence->extern_lock;
}
 
#define dma_fence_lock_irqsave(fence, flags)    \
    spin_lock_irqsave(dma_fence_spinlock(fence), flags)
 
#define dma_fence_unlock_irqrestore(fence, flags)   \
    spin_unlock_irqrestore(dma_fence_spinlock(fence), flags)
 
#define dma_fence_assert_held(fence)    \
    lockdep_assert_held(dma_fence_spinlock(fence));
 
#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
 
void dma_fence_signal(struct dma_fence *fence);
bool dma_fence_check_and_signal(struct dma_fence *fence);
bool dma_fence_check_and_signal_locked(struct dma_fence *fence);
void dma_fence_signal_locked(struct dma_fence *fence);
void dma_fence_signal_timestamp(struct dma_fence *fence, ktime_t timestamp);
void 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);
 
const char __rcu *dma_fence_driver_name(struct dma_fence *fence);
const char __rcu *dma_fence_timeline_name(struct dma_fence *fence);
 
/*
 * dma_fence_test_signaled_flag - Only check whether a fence is signaled yet.
 * @fence: the fence to check
 *
 * This function just checks whether @fence is signaled, without interacting
 * with the fence in any way. The user must, therefore, ensure through other
 * means that fences get signaled eventually.
 *
 * This function uses test_bit(), which is thread-safe. Naturally, this function
 * should be used opportunistically; a fence could get signaled at any moment
 * after the check is done.
 *
 * Return: true if signaled, false otherwise.
 */
static inline bool
dma_fence_test_signaled_flag(struct dma_fence *fence)
{
    return test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags);
}
 
static inline bool
dma_fence_is_signaled_locked(struct dma_fence *fence)
{
    const struct dma_fence_ops *ops;
 
    if (dma_fence_test_signaled_flag(fence))
        return true;
 
    rcu_read_lock();
    ops = rcu_dereference(fence->ops);
    if (ops && ops->signaled && ops->signaled(fence)) {
        rcu_read_unlock();
        dma_fence_signal_locked(fence);
        return true;
    }
    rcu_read_unlock();
 
    return false;
}
 
static inline bool
dma_fence_is_signaled(struct dma_fence *fence)
{
    const struct dma_fence_ops *ops;
 
    if (dma_fence_test_signaled_flag(fence))
        return true;
 
    rcu_read_lock();
    ops = rcu_dereference(fence->ops);
    if (ops && ops->signaled && ops->signaled(fence)) {
        rcu_read_unlock();
        dma_fence_signal(fence);
        return true;
    }
    rcu_read_unlock();
 
    return false;
}
 
static inline bool __dma_fence_is_later(struct dma_fence *fence, u64 f1, u64 f2)
{
    /* 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 (test_bit(DMA_FENCE_FLAG_SEQNO64_BIT, &fence->flags))
        return f1 > f2;
 
    return (int)(lower_32_bits(f1) - lower_32_bits(f2)) > 0;
}
 
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, f1->seqno, f2->seqno);
}
 
static inline bool dma_fence_is_later_or_same(struct dma_fence *f1,
                          struct dma_fence *f2)
{
    return f1 == f2 || dma_fence_is_later(f1, f2);
}
 
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;
}
 
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);
 
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;
}
 
static inline ktime_t dma_fence_timestamp(struct dma_fence *fence)
{
    if (WARN_ON(!test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags)))
        return ktime_get();
 
    while (!test_bit(DMA_FENCE_FLAG_TIMESTAMP_BIT, &fence->flags))
        cpu_relax();
 
    return fence->timestamp;
}
 
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);
 
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;
}
 
void dma_fence_set_deadline(struct dma_fence *fence, ktime_t deadline);
 
struct dma_fence *dma_fence_get_stub(void);
struct dma_fence *dma_fence_allocate_private_stub(ktime_t timestamp);
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;
 
static inline bool dma_fence_is_array(struct dma_fence *fence)
{
    return rcu_access_pointer(fence->ops) == &dma_fence_array_ops;
}
 
static inline bool dma_fence_is_chain(struct dma_fence *fence)
{
    return rcu_access_pointer(fence->ops) == &dma_fence_chain_ops;
}
 
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 */