/* * Copyright 2017 Advanced Micro Devices, Inc. * * Permission is hereby granted, free of charge, to any person obtaining a * copy of this software and associated documentation files (the "Software"), * to deal in the Software without restriction, including without limitation * the rights to use, copy, modify, merge, publish, distribute, sublicense, * and/or sell copies of the Software, and to permit persons to whom the * Software is furnished to do so, subject to the following conditions: * * The above copyright notice and this permission notice shall be included in * all copies or substantial portions of the Software. * * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL * THE COPYRIGHT HOLDER(S) OR AUTHOR(S) BE LIABLE FOR ANY CLAIM, DAMAGES OR * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR * OTHER DEALINGS IN THE SOFTWARE. * */ #ifndef DRM_SCHEDULER_SPSC_QUEUE_H_#define DRM_SCHEDULER_SPSC_QUEUE_H_ #include <linux/atomic.h>#include <linux/preempt.h> /** SPSC lockless queue */ struct spsc_node { 	/* Stores spsc_node* */	struct spsc_node *next;}; struct spsc_queue { 	 struct spsc_node *head; 	/* atomic pointer to struct spsc_node* */	atomic_long_t tail; 	atomic_t job_count;}; static inline void spsc_queue_init(struct spsc_queue *queue){	queue->head = NULL;	atomic_long_set(&queue->tail, (long)&queue->head);	atomic_set(&queue->job_count, 0);} static inline struct spsc_node *spsc_queue_peek(struct spsc_queue *queue){	return queue->head;} static inline int spsc_queue_count(struct spsc_queue *queue){	return atomic_read(&queue->job_count);} static inline bool spsc_queue_push(struct spsc_queue *queue, struct spsc_node *node){	struct spsc_node **tail; 	node->next = NULL; 	preempt_disable(); 	atomic_inc(&queue->job_count);	smp_mb__after_atomic(); 	tail = (struct spsc_node **)atomic_long_xchg(&queue->tail, (long)&node->next);	WRITE_ONCE(*tail, node); 	/*	 * In case of first element verify new node will be visible to the consumer	 * thread when we ping the kernel thread that there is new work to do.	 */	smp_wmb(); 	preempt_enable(); 	return tail == &queue->head;}  static inline struct spsc_node *spsc_queue_pop(struct spsc_queue *queue){	struct spsc_node *next, *node; 	/* Verify reading from memory and not the cache */	smp_rmb(); 	node = READ_ONCE(queue->head); 	if (!node)		return NULL; 	next = READ_ONCE(node->next);	WRITE_ONCE(queue->head, next); 	if (unlikely(!next)) {		/* slowpath for the last element in the queue */ 		if (atomic_long_cmpxchg(&queue->tail,				(long)&node->next, (long) &queue->head) != (long)&node->next) {			/* Updating tail failed wait for new next to appear */			do {				smp_rmb();			} while (unlikely(!(queue->head = READ_ONCE(node->next))));		}	} 	atomic_dec(&queue->job_count);	return node;}   #endif /* DRM_SCHEDULER_SPSC_QUEUE_H_ */