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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 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);
/**
* @set_deadline:
*
* Callback to allow a fence waiter to inform the fence signaler of
* an upcoming deadline, such as vblank, by which point the waiter
* would prefer the fence to be signaled by. This is intended to
* give feedback to the fence signaler to aid in power management
* decisions, such as boosting GPU frequency.
*
* This is called without &dma_fence.lock held, it can be called
* multiple times and from any context. Locking is up to the callee
* if it has some state to manage. If multiple deadlines are set,
* the expectation is to track the soonest one. If the deadline is
* before the current time, it should be interpreted as an immediate
* deadline.
*
* This callback is optional.
*/
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_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_is_later_or_same - return true if f1 is later or same as 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 or the same fence. Both
* fences must be from the same context, since a seqno is not re-used across
* contexts.
*/
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);
}
/**
* 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;
}
/**
* dma_fence_timestamp - helper to get the completion timestamp of a fence
* @fence: fence to get the timestamp from.
*
* After a fence is signaled the timestamp is updated with the signaling time,
* but setting the timestamp can race with tasks waiting for the signaling. This
* helper busy waits for the correct timestamp to appear.
*/
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);
/**
* 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;
}
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;
/**
* 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 */