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1/*2 * Copyright 2017 Advanced Micro Devices, Inc.3 *4 * Permission is hereby granted, free of charge, to any person obtaining a5 * copy of this software and associated documentation files (the "Software"),6 * to deal in the Software without restriction, including without limitation7 * the rights to use, copy, modify, merge, publish, distribute, sublicense,8 * and/or sell copies of the Software, and to permit persons to whom the9 * Software is furnished to do so, subject to the following conditions:10 *11 * The above copyright notice and this permission notice shall be included in12 * all copies or substantial portions of the Software.13 *14 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR15 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,16 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL17 * THE COPYRIGHT HOLDER(S) OR AUTHOR(S) BE LIABLE FOR ANY CLAIM, DAMAGES OR18 * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,19 * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR20 * OTHER DEALINGS IN THE SOFTWARE.21 *22 */23 24#ifndef DRM_SCHEDULER_SPSC_QUEUE_H_25#define DRM_SCHEDULER_SPSC_QUEUE_H_26 27#include <linux/atomic.h>28#include <linux/preempt.h>29 30/** SPSC lockless queue */31 32struct spsc_node {33 34 /* Stores spsc_node* */35 struct spsc_node *next;36};37 38struct spsc_queue {39 40 struct spsc_node *head;41 42 /* atomic pointer to struct spsc_node* */43 atomic_long_t tail;44 45 atomic_t job_count;46};47 48static inline void spsc_queue_init(struct spsc_queue *queue)49{50 queue->head = NULL;51 atomic_long_set(&queue->tail, (long)&queue->head);52 atomic_set(&queue->job_count, 0);53}54 55static inline struct spsc_node *spsc_queue_peek(struct spsc_queue *queue)56{57 return queue->head;58}59 60static inline int spsc_queue_count(struct spsc_queue *queue)61{62 return atomic_read(&queue->job_count);63}64 65static inline bool spsc_queue_push(struct spsc_queue *queue, struct spsc_node *node)66{67 struct spsc_node **tail;68 69 node->next = NULL;70 71 preempt_disable();72 73 tail = (struct spsc_node **)atomic_long_xchg(&queue->tail, (long)&node->next);74 WRITE_ONCE(*tail, node);75 atomic_inc(&queue->job_count);76 77 /*78 * In case of first element verify new node will be visible to the consumer79 * thread when we ping the kernel thread that there is new work to do.80 */81 smp_wmb();82 83 preempt_enable();84 85 return tail == &queue->head;86}87 88 89static inline struct spsc_node *spsc_queue_pop(struct spsc_queue *queue)90{91 struct spsc_node *next, *node;92 93 /* Verify reading from memory and not the cache */94 smp_rmb();95 96 node = READ_ONCE(queue->head);97 98 if (!node)99 return NULL;100 101 next = READ_ONCE(node->next);102 WRITE_ONCE(queue->head, next);103 104 if (unlikely(!next)) {105 /* slowpath for the last element in the queue */106 107 if (atomic_long_cmpxchg(&queue->tail,108 (long)&node->next, (long) &queue->head) != (long)&node->next) {109 /* Updating tail failed wait for new next to appear */110 do {111 smp_rmb();112 } while (unlikely(!(queue->head = READ_ONCE(node->next))));113 }114 }115 116 atomic_dec(&queue->job_count);117 return node;118}119 120 121 122#endif /* DRM_SCHEDULER_SPSC_QUEUE_H_ */123