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// SPDX-License-Identifier: GPL-2.0-only
/*
* Fence mechanism for dma-buf and 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>
*/
#include <linux/slab.h>
#include <linux/export.h>
#include <linux/atomic.h>
#include <linux/dma-fence.h>
#include <linux/sched/signal.h>
#define CREATE_TRACE_POINTS
#include <trace/events/dma_fence.h>
EXPORT_TRACEPOINT_SYMBOL(dma_fence_emit);
EXPORT_TRACEPOINT_SYMBOL(dma_fence_enable_signal);
EXPORT_TRACEPOINT_SYMBOL(dma_fence_signaled);
static DEFINE_SPINLOCK(dma_fence_stub_lock);
static struct dma_fence dma_fence_stub;
/*
* fence context counter: each execution context should have its own
* fence context, this allows checking if fences belong to the same
* context or not. One device can have multiple separate contexts,
* and they're used if some engine can run independently of another.
*/
static atomic64_t dma_fence_context_counter = ATOMIC64_INIT(1);
/**
* DOC: DMA fences overview
*
* DMA fences, represented by &struct dma_fence, are the kernel internal
* synchronization primitive for DMA operations like GPU rendering, video
* encoding/decoding, or displaying buffers on a screen.
*
* A fence is initialized using dma_fence_init() and completed using
* dma_fence_signal(). Fences are associated with a context, allocated through
* dma_fence_context_alloc(), and all fences on the same context are
* fully ordered.
*
* Since the purposes of fences is to facilitate cross-device and
* cross-application synchronization, there's multiple ways to use one:
*
* - Individual fences can be exposed as a &sync_file, accessed as a file
* descriptor from userspace, created by calling sync_file_create(). This is
* called explicit fencing, since userspace passes around explicit
* synchronization points.
*
* - Some subsystems also have their own explicit fencing primitives, like
* &drm_syncobj. Compared to &sync_file, a &drm_syncobj allows the underlying
* fence to be updated.
*
* - Then there's also implicit fencing, where the synchronization points are
* implicitly passed around as part of shared &dma_buf instances. Such
* implicit fences are stored in &struct reservation_object through the
* &dma_buf.resv pointer.
*/
static const char *dma_fence_stub_get_name(struct dma_fence *fence)
{
return "stub";
}
static const struct dma_fence_ops dma_fence_stub_ops = {
.get_driver_name = dma_fence_stub_get_name,
.get_timeline_name = dma_fence_stub_get_name,
};
/**
* dma_fence_get_stub - return a signaled fence
*
* Return a stub fence which is already signaled.
*/
struct dma_fence *dma_fence_get_stub(void)
{
spin_lock(&dma_fence_stub_lock);
if (!dma_fence_stub.ops) {
dma_fence_init(&dma_fence_stub,
&dma_fence_stub_ops,
&dma_fence_stub_lock,
0, 0);
dma_fence_signal_locked(&dma_fence_stub);
}
spin_unlock(&dma_fence_stub_lock);
return dma_fence_get(&dma_fence_stub);
}
EXPORT_SYMBOL(dma_fence_get_stub);
/**
* dma_fence_context_alloc - allocate an array of fence contexts
* @num: amount of contexts to allocate
*
* This function will return the first index of the number of fence contexts
* allocated. The fence context is used for setting &dma_fence.context to a
* unique number by passing the context to dma_fence_init().
*/
u64 dma_fence_context_alloc(unsigned num)
{
WARN_ON(!num);
return atomic64_add_return(num, &dma_fence_context_counter) - num;
}
EXPORT_SYMBOL(dma_fence_context_alloc);
/**
* dma_fence_signal_locked - signal completion of a fence
* @fence: the fence to signal
*
* Signal completion for software callbacks on a fence, this will unblock
* dma_fence_wait() calls and run all the callbacks added with
* dma_fence_add_callback(). Can be called multiple times, but since a fence
* can only go from the unsignaled to the signaled state and not back, it will
* only be effective the first time.
*
* Unlike dma_fence_signal(), this function must be called with &dma_fence.lock
* held.
*
* Returns 0 on success and a negative error value when @fence has been
* signalled already.
*/
int dma_fence_signal_locked(struct dma_fence *fence)
{
struct dma_fence_cb *cur, *tmp;
int ret = 0;
lockdep_assert_held(fence->lock);
if (WARN_ON(!fence))
return -EINVAL;
if (test_and_set_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags)) {
ret = -EINVAL;
/*
* we might have raced with the unlocked dma_fence_signal,
* still run through all callbacks
*/
} else {
fence->timestamp = ktime_get();
set_bit(DMA_FENCE_FLAG_TIMESTAMP_BIT, &fence->flags);
trace_dma_fence_signaled(fence);
}
list_for_each_entry_safe(cur, tmp, &fence->cb_list, node) {
list_del_init(&cur->node);
cur->func(fence, cur);
}
return ret;
}
EXPORT_SYMBOL(dma_fence_signal_locked);
/**
* dma_fence_signal - signal completion of a fence
* @fence: the fence to signal
*
* Signal completion for software callbacks on a fence, this will unblock
* dma_fence_wait() calls and run all the callbacks added with
* dma_fence_add_callback(). Can be called multiple times, but since a fence
* can only go from the unsignaled to the signaled state and not back, it will
* only be effective the first time.
*
* Returns 0 on success and a negative error value when @fence has been
* signalled already.
*/
int dma_fence_signal(struct dma_fence *fence)
{
unsigned long flags;
if (!fence)
return -EINVAL;
if (test_and_set_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags))
return -EINVAL;
fence->timestamp = ktime_get();
set_bit(DMA_FENCE_FLAG_TIMESTAMP_BIT, &fence->flags);
trace_dma_fence_signaled(fence);
if (test_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT, &fence->flags)) {
struct dma_fence_cb *cur, *tmp;
spin_lock_irqsave(fence->lock, flags);
list_for_each_entry_safe(cur, tmp, &fence->cb_list, node) {
list_del_init(&cur->node);
cur->func(fence, cur);
}
spin_unlock_irqrestore(fence->lock, flags);
}
return 0;
}
EXPORT_SYMBOL(dma_fence_signal);
/**
* dma_fence_wait_timeout - sleep until the fence gets signaled
* or until timeout elapses
* @fence: the fence to wait on
* @intr: if true, do an interruptible wait
* @timeout: timeout value in jiffies, or MAX_SCHEDULE_TIMEOUT
*
* Returns -ERESTARTSYS if interrupted, 0 if the wait timed out, or the
* remaining timeout in jiffies on success. Other error values may be
* returned on custom implementations.
*
* Performs a synchronous wait on this fence. It is assumed the caller
* directly or indirectly (buf-mgr between reservation and committing)
* holds a reference to the fence, otherwise the fence might be
* freed before return, resulting in undefined behavior.
*
* See also dma_fence_wait() and dma_fence_wait_any_timeout().
*/
signed long
dma_fence_wait_timeout(struct dma_fence *fence, bool intr, signed long timeout)
{
signed long ret;
if (WARN_ON(timeout < 0))
return -EINVAL;
trace_dma_fence_wait_start(fence);
if (fence->ops->wait)
ret = fence->ops->wait(fence, intr, timeout);
else
ret = dma_fence_default_wait(fence, intr, timeout);
trace_dma_fence_wait_end(fence);
return ret;
}
EXPORT_SYMBOL(dma_fence_wait_timeout);
/**
* dma_fence_release - default relese function for fences
* @kref: &dma_fence.recfount
*
* This is the default release functions for &dma_fence. Drivers shouldn't call
* this directly, but instead call dma_fence_put().
*/
void dma_fence_release(struct kref *kref)
{
struct dma_fence *fence =
container_of(kref, struct dma_fence, refcount);
trace_dma_fence_destroy(fence);
/* Failed to signal before release, could be a refcounting issue */
WARN_ON(!list_empty(&fence->cb_list));
if (fence->ops->release)
fence->ops->release(fence);
else
dma_fence_free(fence);
}
EXPORT_SYMBOL(dma_fence_release);
/**
* dma_fence_free - default release function for &dma_fence.
* @fence: fence to release
*
* This is the default implementation for &dma_fence_ops.release. It calls
* kfree_rcu() on @fence.
*/
void dma_fence_free(struct dma_fence *fence)
{
kfree_rcu(fence, rcu);
}
EXPORT_SYMBOL(dma_fence_free);
/**
* dma_fence_enable_sw_signaling - enable signaling on fence
* @fence: the fence to enable
*
* This will request for sw signaling to be enabled, to make the fence
* complete as soon as possible. This calls &dma_fence_ops.enable_signaling
* internally.
*/
void dma_fence_enable_sw_signaling(struct dma_fence *fence)
{
unsigned long flags;
if (!test_and_set_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT,
&fence->flags) &&
!test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags) &&
fence->ops->enable_signaling) {
trace_dma_fence_enable_signal(fence);
spin_lock_irqsave(fence->lock, flags);
if (!fence->ops->enable_signaling(fence))
dma_fence_signal_locked(fence);
spin_unlock_irqrestore(fence->lock, flags);
}
}
EXPORT_SYMBOL(dma_fence_enable_sw_signaling);
/**
* dma_fence_add_callback - add a callback to be called when the fence
* is signaled
* @fence: the fence to wait on
* @cb: the callback to register
* @func: the function to call
*
* @cb will be initialized by dma_fence_add_callback(), no initialization
* by the caller is required. Any number of callbacks can be registered
* to a fence, but a callback can only be registered to one fence at a time.
*
* Note that the callback can be called from an atomic context. If
* fence is already signaled, this function will return -ENOENT (and
* *not* call the callback).
*
* Add a software callback to the fence. Same restrictions apply to
* refcount as it does to dma_fence_wait(), however the caller doesn't need to
* keep a refcount to fence afterward dma_fence_add_callback() has returned:
* when software access is enabled, the creator of the fence is required to keep
* the fence alive until after it signals with dma_fence_signal(). The callback
|