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/*

 * Fence mechanism for dma-buf to allow for asynchronous dma access

 *

 * Copyright (C) 2012 Canonical Ltd

 * Copyright (C) 2012 Texas Instruments

 *

 * Authors:

 * Rob Clark 

 * Maarten Lankhorst 

 *

 * 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_FENCE_H

#define __LINUX_FENCE_H

#include 

#include 

#include 

#include 

#include 

#include 

#include 

#include 

struct fence;

struct fence_ops;

struct fence_cb;

/**

 * struct fence - software synchronization primitive

 * @refcount: refcount for this fence

 * @ops: 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

 *           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 FENCE_FLAG_* defined below

 * @timestamp: Timestamp when the fence was signaled.

 * @status: Optional, only valid if < 0, must be set before calling

 * 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.

 *

 * FENCE_FLAG_SIGNALED_BIT - fence is already signaled

 * FENCE_FLAG_ENABLE_SIGNAL_BIT - enable_signaling might have been called*

 * 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 fence_signal was called right

 * before this bit was set, it would have been able to set the

 * FENCE_FLAG_SIGNALED_BIT, before enable_signaling was called.

 * Adding a check for FENCE_FLAG_SIGNALED_BIT after setting

 * FENCE_FLAG_ENABLE_SIGNAL_BIT closes this race, and makes sure that

 * after fence_signal was called, any enable_signaling call will have either

 * been completed, or never called at all.

 */

struct fence {

	struct kref refcount;

	const struct fence_ops *ops;

	struct rcu_head rcu;

	struct list_head cb_list;

	spinlock_t *lock;

	unsigned context, seqno;

	unsigned long flags;

	ktime_t timestamp;

	int status;

};

enum fence_flag_bits {

	FENCE_FLAG_SIGNALED_BIT,

	FENCE_FLAG_ENABLE_SIGNAL_BIT,

	FENCE_FLAG_USER_BITS, /* must always be last member */

};

typedef void (*fence_func_t)(struct fence *fence, struct fence_cb *cb);

/**

 * struct fence_cb - callback for fence_add_callback

 * @node: used by fence_add_callback to append this struct to fence::cb_list

 * @func: fence_func_t to call

 *

 * This struct will be initialized by fence_add_callback, additional

 * data can be passed along by embedding fence_cb in another struct.

 */

struct fence_cb {

	struct list_head node;

	fence_func_t func;

};

/**

 * struct fence_ops - operations implemented for fence

 * @get_driver_name: returns the driver name.

 * @get_timeline_name: return the name of the context this fence belongs to.

 * @enable_signaling: enable software signaling of fence.

 * @signaled: [optional] peek whether the fence is signaled, can be null.

 * @wait: custom wait implementation, or fence_default_wait.

 * @release: [optional] called on destruction of fence, can be null

 * @fill_driver_data: [optional] callback to fill in free-form debug info

 * Returns amount of bytes filled, or -errno.

 * @fence_value_str: [optional] fills in the value of the fence as a string

 * @timeline_value_str: [optional] fills in the current value of the timeline

 * as a string

 *

 * Notes on enable_signaling:

 * For fence implementations that have the capability for hw->hw

 * signaling, they can implement this op to enable the necessary

 * irqs, or insert commands into cmdstream, etc.  This is called

 * in the first wait() or 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 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.

 *

 * fence->status may be set in enable_signaling, but only when false is

 * returned.

 *

 * Calling fence_signal before enable_signaling is called allows

 * for a tiny race window in which enable_signaling is called during,

 * before, or after fence_signal. To fight this, it is recommended

 * that before enable_signaling returns true an extra reference is

 * taken on the fence, to be released when the fence is signaled.

 * This will mean fence_signal will still be called twice, but

 * the second time will be a noop since it was already signaled.

 *

 * Notes on signaled:

 * May set fence->status if returning true.

 *

 * Notes on wait:

 * Must not be NULL, set to fence_default_wait for default implementation.

 * the fence_default_wait implementation should work for any fence, as long

 * as enable_signaling works correctly.

 *

 * 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.

 *

 * Notes on release:

 * Can be NULL, this function allows additional commands to run on

 * destruction of the fence. Can be called from irq context.

 * If pointer is set to NULL, kfree will get called instead.

 */

struct fence_ops {

	const char * (*get_driver_name)(struct fence *fence);

	const char * (*get_timeline_name)(struct fence *fence);

	bool (*enable_signaling)(struct fence *fence);

	bool (*signaled)(struct fence *fence);

	signed long (*wait)(struct fence *fence, bool intr, signed long timeout);

	void (*release)(struct fence *fence);

	int (*fill_driver_data)(struct fence *fence, void *data, int size);

	void (*fence_value_str)(struct fence *fence, char *str, int size);

	void (*timeline_value_str)(struct fence *fence, char *str, int size);

};

void fence_init(struct fence *fence, const struct fence_ops *ops,

		spinlock_t *lock, unsigned context, unsigned seqno);

void fence_release(struct kref *kref);

void fence_free(struct fence *fence);

/**

 * fence_get - increases refcount of the fence

 * @fence:	[in]	fence to increase refcount of

 *

 * Returns the same fence, with refcount increased by 1.

 */

static inline struct fence *fence_get(struct fence *fence)

{

	if (fence)

		kref_get(&fence->refcount);

	return fence;

}

/**

 * fence_get_rcu - get a fence from a reservation_object_list with rcu read lock

 * @fence:	[in]	fence to increase refcount of

 *

 * Function returns NULL if no refcount could be obtained, or the fence.

 */

static inline struct fence *fence_get_rcu(struct fence *fence)

{

	if (kref_get_unless_zero(&fence->refcount))

		return fence;

	else

		return NULL;

}

/**

 * fence_put - decreases refcount of the fence

 * @fence:	[in]	fence to reduce refcount of

 */

static inline void fence_put(struct fence *fence)

{

	if (fence)

		kref_put(&fence->refcount, fence_release);

}

int fence_signal(struct fence *fence);

int fence_signal_locked(struct fence *fence);

signed long fence_default_wait(struct fence *fence, bool intr, signed long timeout);

int fence_add_callback(struct fence *fence, struct fence_cb *cb,

		       fence_func_t func);

bool fence_remove_callback(struct fence *fence, struct fence_cb *cb);

void fence_enable_sw_signaling(struct fence *fence);

/**

 * fence_is_signaled_locked - Return an indication if the fence is signaled yet.

 * @fence:	[in]	the fence to check

 *

 * Returns true if the fence was already signaled, false if not. Since this

 * function doesn't enable signaling, it is not guaranteed to ever return

 * true if fence_add_callback, fence_wait or fence_enable_sw_signaling

 * haven't been called before.

 *

 * This function requires fence->lock to be held.

 */

static inline bool

fence_is_signaled_locked(struct fence *fence)

{

	if (test_bit(FENCE_FLAG_SIGNALED_BIT, &fence->flags))

		return true;

	if (fence->ops->signaled && fence->ops->signaled(fence)) {

		fence_signal_locked(fence);

		return true;

	}

	return false;

}

/**

 * fence_is_signaled - Return an indication if the fence is signaled yet.

 * @fence:	[in]	the fence to check

 *

 * Returns true if the fence was already signaled, false if not. Since this

 * function doesn't enable signaling, it is not guaranteed to ever return

 * true if fence_add_callback, fence_wait or fence_enable_sw_signaling

 * haven't been called before.

 *

 * It's recommended for seqno fences to call fence_signal when the

 * operation is complete, it makes it possible to prevent issues from

 * wraparound between time of issue and time of use by checking the return

 * value of this function before calling hardware-specific wait instructions.

 */

static inline bool

fence_is_signaled(struct fence *fence)

{

	if (test_bit(FENCE_FLAG_SIGNALED_BIT, &fence->flags))

		return true;

	if (fence->ops->signaled && fence->ops->signaled(fence)) {

		fence_signal(fence);

		return true;

	}

	return false;

}

/**

 * fence_is_later - return if f1 is chronologically later than f2

 * @f1:	[in]	the first fence from the same context

 * @f2:	[in]	the second fence from the same context

 *

 * Returns true if f1 is chronologically later than f2. Both fences must be

 * from the same context, since a seqno is not re-used across contexts.

 */

static inline bool fence_is_later(struct fence *f1, struct fence *f2)

{

	if (WARN_ON(f1->context != f2->context))

		return false;

	return f1->seqno - f2->seqno < INT_MAX;

}

/**

 * fence_later - return the chronologically later fence

 * @f1:	[in]	the first fence from the same context

 * @f2:	[in]	the second fence from the same context

 *

 * Returns NULL if both fences are signaled, otherwise the fence that would be

 * signaled last. Both fences must be from the same context, since a seqno is

 * not re-used across contexts.

 */

static inline struct fence *fence_later(struct fence *f1, struct fence *f2)

{

	if (WARN_ON(f1->context != f2->context))

		return NULL;

	/*

	 * can't check just FENCE_FLAG_SIGNALED_BIT here, it may never have been

	 * set if enable_signaling wasn't called, and enabling that here is

	 * overkill.

	 */

	if (fence_is_later(f1, f2))

		return fence_is_signaled(f1) ? NULL : f1;

	else

		return fence_is_signaled(f2) ? NULL : f2;

}

signed long fence_wait_timeout(struct fence *, bool intr, signed long timeout);

signed long fence_wait_any_timeout(struct fence **fences, uint32_t count,

				   bool intr, signed long timeout);

/**

 * fence_wait - sleep until the fence gets signaled

 * @fence:	[in]	the fence to wait on

 * @intr:	[in]	if true, do an interruptible wait

 *

 * This function will return -ERESTARTSYS if interrupted by a signal,

 * or 0 if the fence was signaled. Other error values may be

 * returned on custom implementations.

 *

 * Performs a synchronous wait on this fence. It is assumed the caller

 * directly or indirectly holds a reference to the fence, otherwise the

 * fence might be freed before return, resulting in undefined behavior.

 */

static inline signed long fence_wait(struct fence *fence, bool intr)

{

	signed long ret;

	/* Since fence_wait_timeout cannot timeout with

	 * MAX_SCHEDULE_TIMEOUT, only valid return values are

	 * -ERESTARTSYS and MAX_SCHEDULE_TIMEOUT.

	 */

	ret = fence_wait_timeout(fence, intr, MAX_SCHEDULE_TIMEOUT);

	return ret < 0 ? ret : 0;

}

unsigned fence_context_alloc(unsigned num);

#define FENCE_TRACE(f, fmt, args...) \

	do {								\

		struct fence *__ff = (f);				\

	} while (0)

#define FENCE_WARN(f, fmt, args...) \

	do {								\

		struct fence *__ff = (f);				\

		pr_warn("f %u#%u: " fmt, __ff->context, __ff->seqno,	\

			 ##args);					\

	} while (0)

#define FENCE_ERR(f, fmt, args...) \

	do {								\

		struct fence *__ff = (f);				\

		pr_err("f %u#%u: " fmt, __ff->context, __ff->seqno,	\

			##args);					\

	} while (0)

#endif /* __LINUX_FENCE_H */