[PATCH 11/26] dma-fence: Refactor signaling for manual invocation

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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@xxxxxxxxxxxxxxxxxx>
Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
---
 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              |  84 +++++++
 include/linux/dma-fence-types.h             | 252 ++++++++++++++++++++
 include/linux/dma-fence.h                   | 222 +----------------
 7 files changed, 381 insertions(+), 280 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@xxxxxxxxx>
+ * Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxx>
+ *
+ * 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 c092bdf5f0bf..f9ba43a0f4d8 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"
@@ -97,35 +96,6 @@ 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..aa44eb031693
--- /dev/null
+++ b/include/linux/dma-fence-impl.h
@@ -0,0 +1,84 @@
+/* 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@xxxxxxxxx>
+ * Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxx>
+ */
+
+#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);
+	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);
+}
+
+#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..52f48decf23d
--- /dev/null
+++ b/include/linux/dma-fence-types.h
@@ -0,0 +1,252 @@
+/*
+ * 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@xxxxxxxxx>
+ * Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxx>
+ *
+ * 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;
+	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 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);
+};
+
+#endif /* __LINUX_DMA_FENCE_TYPES_H */
diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h
index 05d29dbc7e62..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>
@@ -22,227 +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;
-	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);
 
-- 
2.20.1

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