[PATCH 3/4] dma-fence: Refactor signaling for manual invocation
Koenig, Christian
Christian.Koenig at amd.com
Mon Aug 12 14:34:32 UTC 2019
Am 10.08.19 um 17:34 schrieb Chris Wilson:
> Move the duplicated code within dma-fence.c into the header for wider
> reuse. In the process apply a small micro-optimisation to only prune the
> fence->cb_list once rather than use list_del on every entry.
>
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> ---
> drivers/dma-buf/Makefile | 10 +-
> drivers/dma-buf/dma-fence-trace.c | 28 +++
> drivers/dma-buf/dma-fence.c | 33 +--
> drivers/gpu/drm/i915/gt/intel_breadcrumbs.c | 32 +--
> include/linux/dma-fence-impl.h | 83 +++++++
> include/linux/dma-fence-types.h | 258 ++++++++++++++++++++
> include/linux/dma-fence.h | 228 +----------------
Mhm, I don't really see the value in creating more header files.
Especially I'm pretty sure that the types should stay in dma-fence.h
Christian.
> 7 files changed, 386 insertions(+), 286 deletions(-)
> create mode 100644 drivers/dma-buf/dma-fence-trace.c
> create mode 100644 include/linux/dma-fence-impl.h
> create mode 100644 include/linux/dma-fence-types.h
>
> diff --git a/drivers/dma-buf/Makefile b/drivers/dma-buf/Makefile
> index e8c7310cb800..65c43778e571 100644
> --- a/drivers/dma-buf/Makefile
> +++ b/drivers/dma-buf/Makefile
> @@ -1,6 +1,12 @@
> # SPDX-License-Identifier: GPL-2.0-only
> -obj-y := dma-buf.o dma-fence.o dma-fence-array.o dma-fence-chain.o \
> - reservation.o seqno-fence.o
> +obj-y := \
> + dma-buf.o \
> + dma-fence.o \
> + dma-fence-array.o \
> + dma-fence-chain.o \
> + dma-fence-trace.o \
> + reservation.o \
> + seqno-fence.o
> obj-$(CONFIG_SYNC_FILE) += sync_file.o
> obj-$(CONFIG_SW_SYNC) += sw_sync.o sync_debug.o
> obj-$(CONFIG_UDMABUF) += udmabuf.o
> diff --git a/drivers/dma-buf/dma-fence-trace.c b/drivers/dma-buf/dma-fence-trace.c
> new file mode 100644
> index 000000000000..eb6f282be4c0
> --- /dev/null
> +++ b/drivers/dma-buf/dma-fence-trace.c
> @@ -0,0 +1,28 @@
> +/*
> + * 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 at gmail.com>
> + * Maarten Lankhorst <maarten.lankhorst at 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.
> + */
> +
> +#include <linux/dma-fence-types.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);
> diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c
> index 59ac96ec7ba8..027a6a894abd 100644
> --- a/drivers/dma-buf/dma-fence.c
> +++ b/drivers/dma-buf/dma-fence.c
> @@ -14,15 +14,9 @@
> #include <linux/export.h>
> #include <linux/atomic.h>
> #include <linux/dma-fence.h>
> +#include <linux/dma-fence-impl.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;
>
> @@ -128,7 +122,6 @@ EXPORT_SYMBOL(dma_fence_context_alloc);
> */
> int dma_fence_signal_locked(struct dma_fence *fence)
> {
> - struct dma_fence_cb *cur, *tmp;
> int ret = 0;
>
> lockdep_assert_held(fence->lock);
> @@ -136,7 +129,7 @@ int dma_fence_signal_locked(struct dma_fence *fence)
> if (WARN_ON(!fence))
> return -EINVAL;
>
> - if (test_and_set_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags)) {
> + if (!__dma_fence_signal(fence)) {
> ret = -EINVAL;
>
> /*
> @@ -144,15 +137,10 @@ int dma_fence_signal_locked(struct dma_fence *fence)
> * still run through all callbacks
> */
> } else {
> - fence->timestamp = ktime_get();
> - set_bit(DMA_FENCE_FLAG_TIMESTAMP_BIT, &fence->flags);
> - trace_dma_fence_signaled(fence);
> + __dma_fence_signal__timestamp(fence, ktime_get());
> }
>
> - list_for_each_entry_safe(cur, tmp, &fence->cb_list, node) {
> - list_del_init(&cur->node);
> - cur->func(fence, cur);
> - }
> + __dma_fence_signal__notify(fence);
> return ret;
> }
> EXPORT_SYMBOL(dma_fence_signal_locked);
> @@ -177,21 +165,14 @@ int dma_fence_signal(struct dma_fence *fence)
> if (!fence)
> return -EINVAL;
>
> - if (test_and_set_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags))
> + if (!__dma_fence_signal(fence))
> return -EINVAL;
>
> - fence->timestamp = ktime_get();
> - set_bit(DMA_FENCE_FLAG_TIMESTAMP_BIT, &fence->flags);
> - trace_dma_fence_signaled(fence);
> + __dma_fence_signal__timestamp(fence, ktime_get());
>
> 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);
> - }
> + __dma_fence_signal__notify(fence);
> spin_unlock_irqrestore(fence->lock, flags);
> }
> return 0;
> diff --git a/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c b/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
> index e1bbc9b428cd..65de5c45a233 100644
> --- a/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
> +++ b/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
> @@ -22,8 +22,7 @@
> *
> */
>
> -#include <linux/kthread.h>
> -#include <trace/events/dma_fence.h>
> +#include <linux/dma-fence-impl.h>
> #include <uapi/linux/sched/types.h>
>
> #include "i915_drv.h"
> @@ -98,35 +97,6 @@ check_signal_order(struct intel_context *ce, struct i915_request *rq)
> return true;
> }
>
> -static bool
> -__dma_fence_signal(struct dma_fence *fence)
> -{
> - return !test_and_set_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags);
> -}
> -
> -static void
> -__dma_fence_signal__timestamp(struct dma_fence *fence, ktime_t timestamp)
> -{
> - fence->timestamp = timestamp;
> - set_bit(DMA_FENCE_FLAG_TIMESTAMP_BIT, &fence->flags);
> - trace_dma_fence_signaled(fence);
> -}
> -
> -static void
> -__dma_fence_signal__notify(struct dma_fence *fence)
> -{
> - struct dma_fence_cb *cur, *tmp;
> -
> - lockdep_assert_held(fence->lock);
> - lockdep_assert_irqs_disabled();
> -
> - list_for_each_entry_safe(cur, tmp, &fence->cb_list, node) {
> - INIT_LIST_HEAD(&cur->node);
> - cur->func(fence, cur);
> - }
> - INIT_LIST_HEAD(&fence->cb_list);
> -}
> -
> void intel_engine_breadcrumbs_irq(struct intel_engine_cs *engine)
> {
> struct intel_breadcrumbs *b = &engine->breadcrumbs;
> diff --git a/include/linux/dma-fence-impl.h b/include/linux/dma-fence-impl.h
> new file mode 100644
> index 000000000000..7372021cf082
> --- /dev/null
> +++ b/include/linux/dma-fence-impl.h
> @@ -0,0 +1,83 @@
> +/* 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 at gmail.com>
> + * Maarten Lankhorst <maarten.lankhorst at canonical.com>
> + */
> +
> +#ifndef __LINUX_DMA_FENCE_IMPL_H
> +#define __LINUX_DMA_FENCE_IMPL_H
> +
> +#include <linux/dma-fence.h>
> +#include <linux/lockdep.h>
> +#include <linux/list.h>
> +#include <linux/ktime.h>
> +
> +#include <trace/events/dma_fence.h>
> +
> +/**
> + * __dma_fence_signal: Mark a fence as signaled
> + * @fence: the dma fence to mark
> + *
> + * The first step of the dma_fence_signal() implementation is to atomically
> + * mark the fence as signaled.
> + *
> + * Returns: true if the fence was not previously signaled, false if it was
> + * already signaled.
> + */
> +static inline bool
> +__dma_fence_signal(struct dma_fence *fence)
> +{
> + return !test_and_set_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags);
> +}
> +
> +/**
> + * __dma_fence_signal__timestamp: sets the signaling timestamp
> + * @fence: the dma fence
> + * @timestamp: the monotonic timestamp (e.g. ktime_get_mono())
> + *
> + * The second step of the dma_fence_signal() implementation it to record
> + * the siganling timestamp.
> + *
> + * The dma-fence stores a timestamp of when it was signaled for inspection
> + * by userspace. This timestamp is typically the CPU time at which the
> + * signal was raised, but could be a HW timestamp generated by the event
> + * itself. Either way, it must be set on the signaled fence before
> + * callbacks are notified.
> + */
> +static inline void
> +__dma_fence_signal__timestamp(struct dma_fence *fence, ktime_t timestamp)
> +{
> + fence->timestamp = timestamp;
> + set_bit(DMA_FENCE_FLAG_TIMESTAMP_BIT, &fence->flags);
> + trace_dma_fence_signaled(fence);
> +}
> +
> +/**
> + * __dma_fence_signal__notify: notify observers of the signal event
> + * @fence: the dma fence
> + *
> + * The final step of the dma_fence_signal() implementation is to notify
> + * all observers (dma_fence_add_callback()) of the signal event. This must
> + * be called with the fence->lock already held and irqsoff.
> + */
> +static inline void
> +__dma_fence_signal__notify(struct dma_fence *fence)
> +{
> + struct dma_fence_cb *cur, *tmp;
> +
> + lockdep_assert_held(fence->lock);
> +
> + list_for_each_entry_safe(cur, tmp, &fence->cb_list, node) {
> + INIT_LIST_HEAD(&cur->node);
> + cur->func(fence, cur);
> + }
> + INIT_LIST_HEAD(&fence->cb_list);
> +}
> +
> +#endif /* __LINUX_DMA_FENCE_IMPL_H */
> diff --git a/include/linux/dma-fence-types.h b/include/linux/dma-fence-types.h
> new file mode 100644
> index 000000000000..81e22d9ed174
> --- /dev/null
> +++ b/include/linux/dma-fence-types.h
> @@ -0,0 +1,258 @@
> +/*
> + * 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 at gmail.com>
> + * Maarten Lankhorst <maarten.lankhorst at 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_TYPES_H
> +#define __LINUX_DMA_FENCE_TYPES_H
> +
> +#include <linux/list.h>
> +#include <linux/kref.h>
> +#include <linux/ktime.h>
> +#include <linux/rcupdate.h>
> +#include <linux/spinlock.h>
> +#include <linux/types.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 {
> + struct kref refcount;
> + 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.
> + */
> + union {
> + struct rcu_head rcu;
> + struct list_head cb_list;
> + };
> + spinlock_t *lock;
> + u64 context;
> + u64 seqno;
> + unsigned long flags;
> + ktime_t timestamp;
> + 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 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 through
> + * 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.
> + *
> + * The dma_fence_default_wait implementation should work for any fence,
> + * as long as @enable_signaling works correctly. This hook allows
> + * drivers to have an optimized version for the case where a process
> + * context is already available, e.g. if @enable_signaling for the
> + * general case needs to set up a worker thread.
> + *
> + * 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.
> + *
> + * This callback is optional.
> + */
> + 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);
> +};
> +
> +#endif /* __LINUX_DMA_FENCE_TYPES_H */
> diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h
> index bea1d05cf51e..1c8dd1fbafae 100644
> --- a/include/linux/dma-fence.h
> +++ b/include/linux/dma-fence.h
> @@ -13,6 +13,7 @@
> #ifndef __LINUX_DMA_FENCE_H
> #define __LINUX_DMA_FENCE_H
>
> +#include <linux/dma-fence-types.h>
> #include <linux/err.h>
> #include <linux/wait.h>
> #include <linux/list.h>
> @@ -22,233 +23,6 @@
> #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_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 {
> - struct kref refcount;
> - 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.
> - */
> - union {
> - struct rcu_head rcu;
> - struct list_head cb_list;
> - };
> - spinlock_t *lock;
> - u64 context;
> - u64 seqno;
> - unsigned long flags;
> - ktime_t timestamp;
> - 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.
> - *
> - * The dma_fence_default_wait implementation should work for any fence, as long
> - * as @enable_signaling works correctly. This hook allows drivers to
> - * have an optimized version for the case where a process context is
> - * already available, e.g. if @enable_signaling for the general case
> - * needs to set up a worker thread.
> - *
> - * 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.
> - *
> - * This callback is optional.
> - */
> - 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);
> -};
> -
> void dma_fence_init(struct dma_fence *fence, const struct dma_fence_ops *ops,
> spinlock_t *lock, u64 context, u64 seqno);
>
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