// 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>
#include <linux/seq_file.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 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 dma_resv through the
* &dma_buf.resv pointer.
*/
/**
* DOC: fence cross-driver contract
*
* Since &dma_fence provide a cross driver contract, all drivers must follow the
* same rules:
*
* * Fences must complete in a reasonable time. Fences which represent kernels
* and shaders submitted by userspace, which could run forever, must be backed
* up by timeout and gpu hang recovery code. Minimally that code must prevent
* further command submission and force complete all in-flight fences, e.g.
* when the driver or hardware do not support gpu reset, or if the gpu reset
* failed for some reason. Ideally the driver supports gpu recovery which only
* affects the offending userspace context, and no other userspace
* submissions.
*
* * Drivers may have different ideas of what completion within a reasonable
* time means. Some hang recovery code uses a fixed timeout, others a mix
* between observing forward progress and increasingly strict timeouts.
* Drivers should not try to second guess timeout handling of fences from
* other drivers.
*
* * To ensure there's no deadlocks of dma_fence_wait() against other locks
* drivers should annotate all code required to reach dma_fence_signal(),
* which completes the fences, with dma_fence_begin_signalling() and
* dma_fence_end_signalling().
*
* * Drivers are allowed to call dma_fence_wait() while holding dma_resv_lock().
* This means any code required for fence completion cannot acquire a
* &dma_resv lock. Note that this also pulls in the entire established
* locking hierarchy around dma_resv_lock() and dma_resv_unlock().
*
* * Drivers are allowed to call dma_fence_wait() from their &shrinker
* callbacks. This means any code required for fence completion cannot
* allocate memory with GFP_KERNEL.
*
* * Drivers are allowed to call dma_fence_wait() from their &mmu_notifier
* respectively &mmu_interval_notifier callbacks. This means any code required
* for fence completion cannot allocate memory with GFP_NOFS or GFP_NOIO.
* Only GFP_ATOMIC is permissible, which might fail.
*
* Note that only GPU drivers have a reasonable excuse for both requiring
* &mmu_interval_notifier and &shrinker callbacks at the same time as having to
* track asynchronous compute work using &dma_fence. No driver outside of
* drivers/gpu should ever call dma_fence_wait() in such contexts.
*/
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,
};
static int __init dma_fence_init_stub(void)
{
dma_fence_init(&dma_fence_stub, &dma_fence_stub_ops, NULL, 0, 0);
set_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT,
&dma_fence_stub.flags);
dma_fence_signal(&dma_fence_stub);
return 0;
}
subsys_initcall(dma_fence_init_stub);
/**
* dma_fence_get_stub - return a signaled fence
*
* Return a stub fence which is already signaled. The fence's timestamp
* corresponds to the initialisation time of the linux kernel.
*/
struct dma_fence *dma_fence_get_stub(void)
{
return dma_fence_get(&dma_fence_stub);
}
EXPORT_SYMBOL(dma_fence_get_stub);
/**
* dma_fence_allocate_private_stub - return a private, signaled fence
* @timestamp: timestamp when the fence was signaled
*
* Return a newly allocated and signaled stub fence.
*/
struct dma_fence *dma_fence_allocate_private_stub(ktime_t timestamp)
{
struct dma_fence *fence;
fence = kzalloc_obj(*fence);
if (fence == NULL)
return NULL;
dma_fence_init(fence, &dma_fence_stub_ops, NULL, 0, 0);
set_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT,
&fence->flags);
dma_fence_signal_timestamp(fence, timestamp);
return fence;
}
EXPORT_SYMBOL(dma_fence_allocate_private_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_fetch_add(num, &dma_fence_context_counter);
}
EXPORT_SYMBOL(dma_fence_context_alloc);
/**
* DOC: fence signalling annotation
*
* Proving correctness of all the kernel code around &dma_fence through code
* review and testing is tricky for a few reasons:
*
* * It is a cross-driver contract, and therefore all drivers must follow the
* same rules for lock nesting order, calling contexts for various functions
* and anything else significant for in-kernel interfaces. But it is also
* impossible to test all drivers in a single machine, hence brute-force N vs.
* N testing of all combinations is impossible. Even just limiting to the
* possible combinations is infeasible.
*
* * There is an enormous amount of driver code involved. For render drivers
* there's the tail of command submission, after fences are published,
* scheduler code, interrupt and workers to process job completion,
* and timeout, gpu reset and gpu hang recovery code. Plus for integration
* with core mm with have &mmu_notifier, respectively &mmu_interval_notifier,
* and &shrinker. For modesetting drivers there's the commit tail functions
* between when fences for an atomic modeset are published, and when the
* corresponding vblank completes, including any interrupt processing and
* related workers. Auditing all that code, across all drivers, is not
* feasible.
*
* * Due to how many other subsystems are involved and the locking hierarchies
* this pulls in there is extremely thin wiggle-room for driver-specific
* differences. &dma_fence interacts with almost all of the core memory
* handling through page fault handlers via &dma_resv, dma_resv_lock() and
* dma_resv_unlock(). On the other side it also interacts through all
* allocation sites through &mmu_notifier and &shrinker.
*
* Furthermore lockdep does not handle cross-release dependencies, which means
* any deadlocks between dma_fence_wait() and dma_fence_signal() can't be caught
* at runtime with some quick testing. The simplest example is one thread
* waiting on a &dma_fence while holding a lock::
*
* lock(A);
* dma_fence_wait(B);
* unlock(A);
*
* while the other thread is stuck trying to acquire the same lock, which
* prevents it from signalling the fence the previous thread is stuck waiting
* on::
*
* lock(A);
* unlock(A);
* dma_fence_signal(B);
*
* By manually annotating all code relevant to signalling a &dma_fence we can
* teach lockdep about these dependencies, which also helps with the validation
* headache since now lockdep can check all the rules for us::
*
* cookie = dma_fence_begin_signalling();
* lock(A);
* unlock(A);
* dma_fence_signal(B);
* dma_fence_end_signalling(cookie);
*
* For using dma_fence_begin_signalling() and dma_fence_end_signalling() to
* annotate critical sections the following rules need to be observed:
*
* * All code necessary to complete a &dma_fence must be annotated, from the
* point where a fence is accessible to other threads, to the point where
* dma_fence_signal() is called. Un-annotated code can contain deadlock issues,
* and due to the very strict rules and many corner cases it is infeasible to
* catch these just with review or normal stress testing.
*
* * &struct dma_resv deserves a special note, since the readers are only
* protected by rcu. This means the signalling critical section starts as soon
* as the new fences are installed, even before dma_resv_unlock() is called.
*
* * The only exception are fast paths and opportunistic signalling code, which
* calls dma_fence_signal() purely as an optimization, but is not required to
* guarantee completion of a &dma_fence. The usual example is a wait IOCTL
* which calls dma_fence_signal(), while the mandatory completion path goes
* through a hardware interrupt and possible job completion worker.
*
* * To aid composability of code, the annotations can be freely nested, as long
* as the overall locking hierarchy is consistent. The annotations also work
* both in interrupt and process context. Due to implementation details this
* requires that callers pass an opaque cookie from
* dma_fence_begin_signalling() to dma_fence_end_signalling().
*
* * Validation against the cross driver contract is implemented by priming
* lockdep with the relevant hierarchy at boot-up. This means even just
* testing with a single device is enough to validate a driver, at least as
* far as deadlocks with dma_fence_wait() against dma_fence_signal() are
* concerned.
*/
#ifdef CONFIG_LOCKDEP
static struct lockdep_map dma_fence_lockdep_map = {
.name = "dma_fence_map"
};
/**
* dma_fence_begin_signalling - begin a critical DMA fence signalling section
*
* Drivers should use this to annotate the beginning of any code section
* required to eventually complete &dma_fence by calling dma_fence_signal().
*
* The end of these critical sections are annotated with
* dma_fence_end_signalling().
*
* Returns:
*
* Opaque cookie needed by the implementation, which needs to be passed to
* dma_fence_end_signalling().
*/
bool dma_fence_begin_signalling(void)
{
/* explicitly nesting ... */
if (lock_is_held_type(&dma_fence_lockdep_map, 1))
return true;
/* rely on might_sleep check for soft/hardirq locks */
if (in_atomic())
return true;
/* ... and non-recursive successful read_trylock */
lock_acquire(&dma_fence_lockdep_map, 0, 1, 1, 1, NULL, _RET_IP_);
return false;
}
EXPORT_SYMBOL(dma_fence_begin_signalling);
/**
* dma_fence_end_signalling - end a critical DMA fence signalling section
* @cookie: opaque cookie from dma_fence_begin_signalling()
*
* Closes a critical section annotation opened by dma_fence_begin_signalling().
*/
void dma_fence_end_signalling(bool cookie)
{
if (cookie)
return;
lock_release(&dma_fence_lockdep_map, _RET_IP_);
}
EXPORT_SYMBOL(dma_fence_end_signalling);
void __dma_fence_might_wait(void)
{
bool tmp;
tmp = lock_is_held_type(&dma_fence_lockdep_map, 1);
if (tmp)
lock_release(&dma_fence_lockdep_map, _THIS_IP_);
lock_map_acquire(&dma_fence_lockdep_map);
lock_map_release(&dma_fence_lockdep_map);
if (tmp)
lock_acquire(&dma_fence_lockdep_map, 0, 1, 1, 1, NULL, _THIS_IP_);
}
#endif
/**
* dma_fence_signal_timestamp_locked - signal completion of a fence
* @fence: the fence to signal
* @timestamp: fence signal timestamp in kernel's CLOCK_MONOTONIC time domain
*
* 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. Set the timestamp provided as the fence
* signal timestamp.
*
* Unlike dma_fence_signal_timestamp(), this function must be called with
* &dma_fence.lock held.
*/
void dma_fence_signal_timestamp_locked(struct dma_fence *fence,
ktime_t timestamp)
{
const struct dma_fence_ops *ops;
struct dma_fence_cb *cur, *tmp;
struct list_head cb_list;
dma_fence_assert_held(fence);
if (unlikely(test_and_set_bit(DMA_FENCE_FLAG_SIGNALED_BIT,
&fence->flags)))
return;
trace_dma_fence_signaled(fence);
/*
* When neither a release nor a wait operation is specified set the ops
* pointer to NULL to allow the fence structure to become independent
* from who originally issued it.
*/
ops = rcu_dereference_protected(fence->ops, true);
if (!ops->release && !ops->wait)
RCU_INIT_POINTER(fence->ops, NULL);
/* Stash the cb_list before replacing it with the timestamp */
list_replace(&fence->cb_list, &cb_list);
fence->timestamp = timestamp;
set_bit(DMA_FENCE_FLAG_TIMESTAMP_BIT, &fence->flags);
list_for_each_entry_safe(cur, tmp, &cb_list, node) {
INIT_LIST_HEAD(&cur->node);
cur->func(fence, cur);
}
}
EXPORT_SYMBOL(dma_fence_signal_timestamp_locked);
/**
* dma_fence_signal_timestamp - signal completion of a fence
* @fence: the fence to signal
* @timestamp: fence signal timestamp in kernel's CLOCK_MONOTONIC time domain
*
* 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. Set the timestamp provided as the fence
* signal timestamp.
*/
void dma_fence_signal_timestamp(struct dma_fence *fence, ktime_t timestamp)
{
unsigned long flags;
if (WARN_ON(!fence))
return;
dma_fence_lock_irqsave(fence, flags);
dma_fence_signal_timestamp_locked(fence, timestamp);
dma_fence_unlock_irqrestore(fence, flags);
}
EXPORT_SYMBOL(dma_fence_signal_timestamp);
/**
* 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.
*/
void dma_fence_signal_locked(struct dma_fence *fence)
{
dma_fence_signal_timestamp_locked(fence, ktime_get());
}
EXPORT_SYMBOL(dma_fence_signal_locked);
/**
* dma_fence_check_and_signal_locked - signal the fence if it's not yet signaled
* @fence: the fence to check and signal
*
* Checks whether a fence was signaled and signals it if it was not yet signaled.
*
* Unlike dma_fence_check_and_signal(), this function must be called with
* &struct dma_fence.lock being held.
*
* Return: true if fence has been signaled already, false otherwise.
*/
bool dma_fence_check_and_signal_locked(struct dma_fence *fence)
{
bool ret;
ret = dma_fence_test_signaled_flag(fence);
dma_fence_signal_locked(fence);
return ret;
}
EXPORT_SYMBOL(dma_fence_check_and_signal_locked);
/**
* dma_fence_check_and_signal - signal the fence if it's not yet signaled
* @fence: the fence to check and signal
*
* Checks whether a fence was signaled and signals it if it was not yet signaled.
* All this is done in a race-free manner.
*
* Return: true if fence has been signaled already, false otherwise.
*/
bool dma_fence_check_and_signal(struct dma_fence *fence)
{
unsigned long flags;
bool ret;
dma_fence_lock_irqsave(fence, flags);
ret = dma_fence_check_and_signal_locked(fence);
dma_fence_unlock_irqrestore(fence, flags);
return ret;
}
EXPORT_SYMBOL(dma_fence_check_and_signal);
/**
* 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.
*/
void dma_fence_signal(struct dma_fence *fence)
{
unsigned long flags;
bool tmp;
if (WARN_ON(!fence))
return;
tmp = dma_fence_begin_signalling();
dma_fence_lock_irqsave(fence, flags);
dma_fence_signal_timestamp_locked(fence, ktime_get());
dma_fence_unlock_irqrestore(fence, flags);
dma_fence_end_signalling(tmp);
}
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)
{
const struct dma_fence_ops *ops;
signed long ret;
if (WARN_ON(timeout < 0))
return -EINVAL;
might_sleep();
__dma_fence_might_wait();
dma_fence_enable_signaling(fence);
rcu_read_lock();
ops = rcu_dereference(fence->ops);
trace_dma_fence_wait_start(fence);
if (ops && ops->wait) {
/*
* Implementing the wait ops is deprecated and not supported for
* issuers of fences who need their lifetime to be independent
* of their module after they signal, so it is ok to use the
* ops outside the RCU protected section.
*/
rcu_read_unlock();
ret = ops->wait(fence, intr, timeout);
} else {
rcu_read_unlock();
ret = dma_fence_default_wait(fence, intr, timeout);
}
if (trace_dma_fence_wait_end_enabled()) {
rcu_read_lock();
trace_dma_fence_wait_end(fence);
rcu_read_unlock();
}
return ret;
}
EXPORT_SYMBOL(dma_fence_wait_timeout);
/**
* dma_fence_release - default release 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);
const struct dma_fence_ops *ops;
rcu_read_lock();
trace_dma_fence_destroy(fence);
if (!list_empty(&fence->cb_list) &&
!dma_fence_test_signaled_flag(fence)) {
const char __rcu *timeline;
const char __rcu *driver;
unsigned long flags;
driver = dma_fence_driver_name(fence);
timeline = dma_fence_timeline_name(fence);
WARN(1,
"Fence %s:%s:%llx:%llx released with pending signals!\n",
rcu_dereference(driver), rcu_dereference(timeline),
fence->context, fence->seqno);
/*
* Failed to signal before release, likely a refcounting issue.
*
* This should never happen, but if it does make sure that we
* don't leave chains dangling. We set the error flag first
* so that the callbacks know this signal is due to an error.
*/
dma_fence_lock_irqsave(fence, flags);
fence->error = -EDEADLK;
dma_fence_signal_locked(fence);
dma_fence_unlock_irqrestore(fence, flags);
}
ops = rcu_dereference(fence->ops);
if (ops && ops->release)
ops->release(fence);
else
dma_fence_free(fence);
rcu_read_unlock();
}
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);
static bool __dma_fence_enable_signaling(struct dma_fence *fence)
{
const struct dma_fence_ops *ops;
bool was_set;
dma_fence_assert_held(fence);
was_set = test_and_set_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT,
&fence->flags);
if (dma_fence_test_signaled_flag(fence))
return false;
rcu_read_lock();
ops = rcu_dereference(fence->ops);
if (!was_set && ops && ops->enable_signaling) {
trace_dma_fence_enable_signal(fence);
if (!ops->enable_signaling(fence)) {
rcu_read_unlock();
dma_fence_signal_locked(fence);
return false;
}
}
rcu_read_unlock();
return true;
}
/**
* dma_fence_enable_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_signaling(struct dma_fence *fence)
{
unsigned long flags;
dma_fence_lock_irqsave(fence, flags);
__dma_fence_enable_signaling(fence);
dma_fence_unlock_irqrestore(fence, flags);
}
EXPORT_SYMBOL(dma_fence_enable_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
*
* Add a software callback to the fence. The caller should keep a reference to
* the fence.
*
* @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.
*
* If fence is already signaled, this function will return -ENOENT (and
* *not* call the callback).
*
* Note that the callback can be called from an atomic context or irq context.
*
* Returns 0 in case of success, -ENOENT if the fence is already signaled
* and -EINVAL in case of error.
*/
int dma_fence_add_callback(struct dma_fence *fence, struct dma_fence_cb *cb,
dma_fence_func_t func)
{
unsigned long flags;
int ret = 0;
if (WARN_ON(!fence || !func))
return -EINVAL;
if (dma_fence_test_signaled_flag(fence)) {
INIT_LIST_HEAD(&cb->node);
return -ENOENT;
}
dma_fence_lock_irqsave(fence, flags);
if (__dma_fence_enable_signaling(fence)) {
cb->func = func;
list_add_tail(&cb->node, &fence->cb_list);
} else {
INIT_LIST_HEAD(&cb->node);
ret = -ENOENT;
}
dma_fence_unlock_irqrestore(fence, flags);
return ret;
}
EXPORT_SYMBOL(dma_fence_add_callback);
/**
* dma_fence_get_status - returns the status upon completion
* @fence: the dma_fence to query
*
* This wraps dma_fence_get_status_locked() to return the error status
* condition on a signaled fence. See dma_fence_get_status_locked() for more
* details.
*
* 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.
*/
int dma_fence_get_status(struct dma_fence *fence)
{
unsigned long flags;
int status;
dma_fence_lock_irqsave(fence, flags);
status = dma_fence_get_status_locked(fence);
dma_fence_unlock_irqrestore(fence, flags);
return status;
}
EXPORT_SYMBOL(dma_fence_get_status);
/**
* dma_fence_remove_callback - remove a callback from the signaling list
* @fence: the fence to wait on
* @cb: the callback to remove
*
* Remove a previously queued callback from the fence. This function returns
* true if the callback is successfully removed, or false if the fence has
* already been signaled.
*
* *WARNING*:
* Cancelling a callback should only be done if you really know what you're
* doing, since deadlocks and race conditions could occur all too easily. For
* this reason, it should only ever be done on hardware lockup recovery,
* with a reference held to the fence.
*
* Behaviour is undefined if @cb has not been added to @fence using
* dma_fence_add_callback() beforehand.
*/
bool
dma_fence_remove_callback(struct dma_fence *fence, struct dma_fence_cb *cb)
{
unsigned long flags;
bool ret;
dma_fence_lock_irqsave(fence, flags);
ret = !list_empty(&cb->node);
if (ret)
list_del_init(&cb->node);
dma_fence_unlock_irqrestore(fence, flags);
return ret;
}
EXPORT_SYMBOL(dma_fence_remove_callback);
struct default_wait_cb {
struct dma_fence_cb base;
struct task_struct *task;
};
static void
dma_fence_default_wait_cb(struct dma_fence *fence, struct dma_fence_cb *cb)
{
struct default_wait_cb *wait =
container_of(cb, struct default_wait_cb, base);
wake_up_state(wait->task, TASK_NORMAL);
}
/**
* dma_fence_default_wait - default 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. If timeout is zero the value one is
* returned if the fence is already signaled for consistency with other
* functions taking a jiffies timeout.
*/
signed long
dma_fence_default_wait(struct dma_fence *fence, bool intr, signed long timeout)
{
struct default_wait_cb cb;
unsigned long flags;
signed long ret = timeout ? timeout : 1;
dma_fence_lock_irqsave(fence, flags);
if (dma_fence_test_signaled_flag(fence))
goto out;
if (intr && signal_pending(current)) {
ret = -ERESTARTSYS;
goto out;
}
if (!timeout) {
ret = 0;
goto out;
}
cb.base.func = dma_fence_default_wait_cb;
cb.task = current;
list_add(&cb.base.node, &fence->cb_list);
while (!dma_fence_test_signaled_flag(fence) && ret > 0) {
if (intr)
__set_current_state(TASK_INTERRUPTIBLE);
else
__set_current_state(TASK_UNINTERRUPTIBLE);
dma_fence_unlock_irqrestore(fence, flags);
ret = schedule_timeout(ret);
dma_fence_lock_irqsave(fence, flags);
if (ret > 0 && intr && signal_pending(current))
ret = -ERESTARTSYS;
}
if (!list_empty(&cb.base.node))
list_del(&cb.base.node);
__set_current_state(TASK_RUNNING);
out:
dma_fence_unlock_irqrestore(fence, flags);
return ret;
}
EXPORT_SYMBOL(dma_fence_default_wait);
static bool
dma_fence_test_signaled_any(struct dma_fence **fences, uint32_t count,
uint32_t *idx)
{
int i;
for (i = 0; i < count; ++i) {
struct dma_fence *fence = fences[i];
if (dma_fence_test_signaled_flag(fence)) {
if (idx)
*idx = i;
return true;
}
}
return false;
}
/**
* dma_fence_wait_any_timeout - sleep until any fence gets signaled
* or until timeout elapses
* @fences: array of fences to wait on
* @count: number of fences to wait on
* @intr: if true, do an interruptible wait
* @timeout: timeout value in jiffies, or MAX_SCHEDULE_TIMEOUT
* @idx: used to store the first signaled fence index, meaningful only on
* positive return
*
* Returns -EINVAL on custom fence wait implementation, -ERESTARTSYS if
* interrupted, 0 if the wait timed out, or the remaining timeout in jiffies
* on success.
*
* Synchronous waits for the first fence in the array to be signaled. The
* caller needs to hold a reference to all fences in the array, otherwise a
* fence might be freed before return, resulting in undefined behavior.
*
* See also dma_fence_wait() and dma_fence_wait_timeout().
*/
signed long
dma_fence_wait_any_timeout(struct dma_fence **fences, uint32_t count,
bool intr, signed long timeout, uint32_t *idx)
{
struct default_wait_cb *cb;
signed long ret = timeout;
unsigned i;
if (WARN_ON(!fences || !count || timeout < 0))
return -EINVAL;
if (timeout == 0) {
for (i = 0; i < count; ++i)
if (dma_fence_is_signaled(fences[i])) {
if (idx)
*idx = i;
return 1;
}
return 0;
}
cb = kzalloc_objs(struct default_wait_cb, count);
if (cb == NULL) {
ret = -ENOMEM;
goto err_free_cb;
}
for (i = 0; i < count; ++i) {
struct dma_fence *fence = fences[i];
cb[i].task = current;
if (dma_fence_add_callback(fence, &cb[i].base,
dma_fence_default_wait_cb)) {
/* This fence is already signaled */
if (idx)
*idx = i;
goto fence_rm_cb;
}
}
while (ret > 0) {
if (intr)
set_current_state(TASK_INTERRUPTIBLE);
else
set_current_state(TASK_UNINTERRUPTIBLE);
if (dma_fence_test_signaled_any(fences, count, idx))
break;
ret = schedule_timeout(ret);
if (ret > 0 && intr && signal_pending(current))
ret = -ERESTARTSYS;
}
__set_current_state(TASK_RUNNING);
fence_rm_cb:
while (i-- > 0)
dma_fence_remove_callback(fences[i], &cb[i].base);
err_free_cb:
kfree(cb);
return ret;
}
EXPORT_SYMBOL(dma_fence_wait_any_timeout);
/**
* DOC: deadline hints
*
* In an ideal world, it would be possible to pipeline a workload sufficiently
* that a utilization based device frequency governor could arrive at a minimum
* frequency that meets the requirements of the use-case, in order to minimize
* power consumption. But in the real world there are many workloads which
* defy this ideal. For example, but not limited to:
*
* * Workloads that ping-pong between device and CPU, with alternating periods
* of CPU waiting for device, and device waiting on CPU. This can result in
* devfreq and cpufreq seeing idle time in their respective domains and in
* result reduce frequency.
*
* * Workloads that interact with a periodic time based deadline, such as double
* buffered GPU rendering vs vblank sync'd page flipping. In this scenario,
* missing a vblank deadline results in an *increase* in idle time on the GPU
* (since it has to wait an additional vblank period), sending a signal to
* the GPU's devfreq to reduce frequency, when in fact the opposite is what is
* needed.
*
* To this end, deadline hint(s) can be set on a &dma_fence via &dma_fence_set_deadline
* (or indirectly via userspace facing ioctls like &sync_set_deadline).
* The deadline hint provides a way for the waiting driver, or userspace, to
* convey an appropriate sense of urgency to the signaling driver.
*
* A deadline hint is given in absolute ktime (CLOCK_MONOTONIC for userspace
* facing APIs). The time could either be some point in the future (such as
* the vblank based deadline for page-flipping, or the start of a compositor's
* composition cycle), or the current time to indicate an immediate deadline
* hint (Ie. forward progress cannot be made until this fence is signaled).
*
* Multiple deadlines may be set on a given fence, even in parallel. See the
* documentation for &dma_fence_ops.set_deadline.
*
* The deadline hint is just that, a hint. The driver that created the fence
* may react by increasing frequency, making different scheduling choices, etc.
* Or doing nothing at all.
*/
/**
* dma_fence_set_deadline - set desired fence-wait deadline hint
* @fence: the fence that is to be waited on
* @deadline: the time by which the waiter hopes for the fence to be
* signaled
*
* Give the fence signaler a hint about 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
* if a periodic vblank deadline is approaching but the fence is not
* yet signaled..
*/
void dma_fence_set_deadline(struct dma_fence *fence, ktime_t deadline)
{
const struct dma_fence_ops *ops;
rcu_read_lock();
ops = rcu_dereference(fence->ops);
if (ops && ops->set_deadline && !dma_fence_is_signaled(fence))
ops->set_deadline(fence, deadline);
rcu_read_unlock();
}
EXPORT_SYMBOL(dma_fence_set_deadline);
/**
* dma_fence_describe - Dump fence description into seq_file
* @fence: the fence to describe
* @seq: the seq_file to put the textual description into
*
* Dump a textual description of the fence and it's state into the seq_file.
*/
void dma_fence_describe(struct dma_fence *fence, struct seq_file *seq)
{
const char __rcu *timeline = (const char __rcu *)"";
const char __rcu *driver = (const char __rcu *)"";
const char *signaled = "";
rcu_read_lock();
if (!dma_fence_is_signaled(fence)) {
timeline = dma_fence_timeline_name(fence);
driver = dma_fence_driver_name(fence);
signaled = "un";
}
seq_printf(seq, "%llu:%llu %s %s %ssignalled\n",
fence->context, fence->seqno, timeline, driver,
signaled);
rcu_read_unlock();
}
EXPORT_SYMBOL(dma_fence_describe);
static void
__dma_fence_init(struct dma_fence *fence, const struct dma_fence_ops *ops,
spinlock_t *lock, u64 context, u64 seqno, unsigned long flags)
{
BUG_ON(!ops || !ops->get_driver_name || !ops->get_timeline_name);
kref_init(&fence->refcount);
/*
* While it is counter intuitive to protect a constant function pointer
* table by RCU it allows modules to wait for an RCU grace period
* before they unload, to make sure that nobody is executing their
* functions any more.
*/
RCU_INIT_POINTER(fence->ops, ops);
INIT_LIST_HEAD(&fence->cb_list);
fence->context = context;
fence->seqno = seqno;
fence->flags = flags | BIT(DMA_FENCE_FLAG_INITIALIZED_BIT);
if (lock) {
fence->extern_lock = lock;
} else {
spin_lock_init(&fence->inline_lock);
fence->flags |= BIT(DMA_FENCE_FLAG_INLINE_LOCK_BIT);
}
fence->error = 0;
trace_dma_fence_init(fence);
}
/**
* dma_fence_init - Initialize a custom fence.
* @fence: the fence to initialize
* @ops: the dma_fence_ops for operations on this fence
* @lock: optional irqsafe spinlock to use for locking this fence
* @context: the execution context this fence is run on
* @seqno: a linear increasing sequence number for this context
*
* Initializes an allocated fence, the caller doesn't have to keep its
* refcount after committing with this fence, but it will need to hold a
* refcount again if &dma_fence_ops.enable_signaling gets called.
*
* context and seqno are used for easy comparison between fences, allowing
* to check which fence is later by simply using dma_fence_later().
*
* External locks are a relic of legacy use cases that needed a shared lock
* to serialize signaling when no out-of-order signaling was possible through
* &dma_fence_ops.signaled. Drivers have abandoned this concept since the
* introduction of the callback, but the external lock is still around. New
* users MUST NOT use external locks, as they force the issuer to outlive all
* fences that reference the lock.
*/
void
dma_fence_init(struct dma_fence *fence, const struct dma_fence_ops *ops,
spinlock_t *lock, u64 context, u64 seqno)
{
__dma_fence_init(fence, ops, lock, context, seqno, 0UL);
}
EXPORT_SYMBOL(dma_fence_init);
/**
* dma_fence_init64 - Initialize a custom fence with 64-bit seqno support.
* @fence: the fence to initialize
* @ops: the dma_fence_ops for operations on this fence
* @lock: optional irqsafe spinlock to use for locking this fence
* @context: the execution context this fence is run on
* @seqno: a linear increasing sequence number for this context
*
* Initializes an allocated fence, the caller doesn't have to keep its
* refcount after committing with this fence, but it will need to hold a
* refcount again if &dma_fence_ops.enable_signaling gets called.
*
* Context and seqno are used for easy comparison between fences, allowing
* to check which fence is later by simply using dma_fence_later().
*
* New users MUST NOT use external locks. Check the documentation in
* dma_fence_init() to understand the motives behind the legacy use cases.
*/
void
dma_fence_init64(struct dma_fence *fence, const struct dma_fence_ops *ops,
spinlock_t *lock, u64 context, u64 seqno)
{
__dma_fence_init(fence, ops, lock, context, seqno,
BIT(DMA_FENCE_FLAG_SEQNO64_BIT));
}
EXPORT_SYMBOL(dma_fence_init64);
/**
* dma_fence_driver_name - Access the driver name
* @fence: the fence to query
*
* Returns a driver name backing the dma-fence implementation.
*
* IMPORTANT CONSIDERATION:
* Dma-fence contract stipulates that access to driver provided data (data not
* directly embedded into the object itself), such as the &dma_fence.lock and
* memory potentially accessed by the &dma_fence.ops functions, is forbidden
* after the fence has been signalled. Drivers are allowed to free that data,
* and some do.
*
* To allow safe access drivers are mandated to guarantee a RCU grace period
* between signalling the fence and freeing said data.
*
* As such access to the driver name is only valid inside a RCU locked section.
* The pointer MUST be both queried and USED ONLY WITHIN a SINGLE block guarded
* by the &rcu_read_lock and &rcu_read_unlock pair.
*/
const char __rcu *dma_fence_driver_name(struct dma_fence *fence)
{
const struct dma_fence_ops *ops;
/* RCU protection is required for safe access to returned string */
ops = rcu_dereference(fence->ops);
if (ops)
return (const char __rcu *)ops->get_driver_name(fence);
else
return (const char __rcu *)"detached-driver";
}
EXPORT_SYMBOL(dma_fence_driver_name);
/**
* dma_fence_timeline_name - Access the timeline name
* @fence: the fence to query
*
* Returns a timeline name provided by the dma-fence implementation.
*
* IMPORTANT CONSIDERATION:
* Dma-fence contract stipulates that access to driver provided data (data not
* directly embedded into the object itself), such as the &dma_fence.lock and
* memory potentially accessed by the &dma_fence.ops functions, is forbidden
* after the fence has been signalled. Drivers are allowed to free that data,
* and some do.
*
* To allow safe access drivers are mandated to guarantee a RCU grace period
* between signalling the fence and freeing said data.
*
* As such access to the driver name is only valid inside a RCU locked section.
* The pointer MUST be both queried and USED ONLY WITHIN a SINGLE block guarded
* by the &rcu_read_lock and &rcu_read_unlock pair.
*/
const char __rcu *dma_fence_timeline_name(struct dma_fence *fence)
{
const struct dma_fence_ops *ops;
/* RCU protection is required for safe access to returned string */
ops = rcu_dereference(fence->ops);
if (ops)
return (const char __rcu *)ops->get_timeline_name(fence);
else
return (const char __rcu *)"signaled-timeline";
}
EXPORT_SYMBOL(dma_fence_timeline_name);
