sys/dev/drm/linux_tasklet.c

   1 /*
   2  * Copyright (c) 2020 François Tigeot <ftigeot@wolfpond.org>
   3  * All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice unmodified, this list of conditions, and the following
  10  *    disclaimer.
  11  * 2. Redistributions in binary form must reproduce the above copyright
  12  *    notice, this list of conditions and the following disclaimer in the
  13  *    documentation and/or other materials provided with the distribution.
  14  *
  15  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
  16  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  17  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  18  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
  19  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  20  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  21  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  22  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  23  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  24  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  25  */
  26
  27 #include <linux/interrupt.h>
  28 #include <linux/slab.h>
  29
  30 #include <sys/kthread.h>
  31
  32 /*
  33  * Linux tasklet constraints:
  34  * - tasklets that have the same type cannot be run on multiple processors at
  35  *   the same time
  36  * - tasklets always run on the processor from which they were originally
  37  *   submitted
  38  * - when a tasklet is scheduled, its state is set to TASKLET_STATE_SCHED,
  39  *   and the tasklet added to a queue
  40  * - during the execution of its function, the tasklet state is set to
  41  *   TASKLET_STATE_RUN and the TASKLET_STATE_SCHED state is removed
  42  */
  43
  44 struct tasklet_entry {
  45         struct tasklet_struct *ts;
  46         SLIST_ENTRY(tasklet_entry) tasklet_entries;
  47 };
  48
  49 static struct lock tasklet_lock = LOCK_INITIALIZER("dltll", 0, LK_CANRECURSE);
  50
  51 static struct thread *tasklet_td = NULL;
  52 SLIST_HEAD(tasklet_list_head, tasklet_entry) tlist = SLIST_HEAD_INITIALIZER(tlist);
  53 SLIST_HEAD(tasklet_hi_list_head, tasklet_entry) tlist_hi = SLIST_HEAD_INITIALIZER(tlist_hi);
  54
  55 static int tasklet_pending = 0;
  56
  57 #define PROCESS_TASKLET_LIST(which_list) do { \
  58         SLIST_FOREACH_MUTABLE(te, &which_list, tasklet_entries, tmp_te) { \
  59                 struct tasklet_struct *t = te->ts;                      \
  60                                                                         \
  61                 /*                                                      \
  62                    This tasklet is dying, remove it from the list.      \
  63                    We allow to it to run one last time if it has        \
  64                    already been scheduled.                              \
  65                 */                                                      \
  66                 if (test_bit(TASKLET_IS_DYING, &t->state)) {            \
  67                         kprintf("tasklet: killing %p\n", t);            \
  68                         SLIST_REMOVE(&which_list, te, tasklet_entry, tasklet_entries); \
  69                         kfree(te);                                      \
  70                 }                                                       \
  71                                                                         \
  72                 /* This tasklet is not scheduled, try the next one */   \
  73                 if (!test_bit(TASKLET_STATE_SCHED, &t->state))          \
  74                         continue;                                       \
  75                                                                         \
  76                 clear_bit(TASKLET_STATE_SCHED, &t->state);              \
  77                 set_bit(TASKLET_STATE_RUN, &t->state);                  \
  78                                                                         \
  79                 lockmgr(&tasklet_lock, LK_RELEASE);                     \
  80                 if (t->func)                                            \
  81                         t->func(t->data);                               \
  82                 lockmgr(&tasklet_lock, LK_EXCLUSIVE);                   \
  83                                                                         \
  84                 clear_bit(TASKLET_STATE_RUN, &t->state);                \
  85         }                                                               \
  86 } while (0)
  87
  88 /* XXX runners should be CPU-specific */
  89 static void
  90 tasklet_runner(void *arg)
  91 {
  92         struct tasklet_entry *te, *tmp_te;
  93
  94         lockmgr(&tasklet_lock, LK_EXCLUSIVE);
  95         while (1) {
  96                 /*
  97                    Only sleep if we haven't been raced by a _schedule()
  98                    call during an unlock window
  99                 */
 100                 if (tasklet_pending == 0) {
 101                         lksleep(&tasklet_runner, &tasklet_lock, 0, "tkidle", 0);
 102                 }
 103                 tasklet_pending = 0;
 104
 105                 /* Process hi tasklets first */
 106                 PROCESS_TASKLET_LIST(tlist_hi);
 107                 PROCESS_TASKLET_LIST(tlist);
 108         }
 109         lockmgr(&tasklet_lock, LK_RELEASE);
 110 }
 111
 112 void
 113 tasklet_init(struct tasklet_struct *t,
 114              void (*func)(unsigned long), unsigned long data)
 115 {
 116         t->state = 0;
 117         t->func = func;
 118         t->data = data;
 119 }
 120
 121 void
 122 tasklet_schedule(struct tasklet_struct *t)
 123 {
 124         struct tasklet_entry *te;
 125
 126         lockmgr(&tasklet_lock, LK_EXCLUSIVE);
 127         set_bit(TASKLET_STATE_SCHED, &t->state);
 128
 129         SLIST_FOREACH(te, &tlist, tasklet_entries) {
 130                 if (te->ts == t)
 131                         goto found_and_done;
 132         }
 133
 134         te = kzalloc(sizeof(struct tasklet_entry), M_WAITOK);
 135         te->ts = t;
 136         SLIST_INSERT_HEAD(&tlist, te, tasklet_entries);
 137
 138 found_and_done:
 139         /* schedule the runner thread on the local cpu core */
 140         tasklet_pending = 1;
 141         wakeup(&tasklet_runner);
 142         lockmgr(&tasklet_lock, LK_RELEASE);
 143 }
 144
 145 void
 146 tasklet_hi_schedule(struct tasklet_struct *t)
 147 {
 148         struct tasklet_entry *te;
 149
 150         lockmgr(&tasklet_lock, LK_EXCLUSIVE);
 151         set_bit(TASKLET_STATE_SCHED, &t->state);
 152
 153         SLIST_FOREACH(te, &tlist_hi, tasklet_entries) {
 154                 if (te->ts == t)
 155                         goto found_and_done;
 156         }
 157
 158         te = kzalloc(sizeof(struct tasklet_entry), M_WAITOK);
 159         te->ts = t;
 160         SLIST_INSERT_HEAD(&tlist_hi, te, tasklet_entries);
 161
 162 found_and_done:
 163         /* schedule the runner thread on the local cpu core */
 164         tasklet_pending = 1;
 165         wakeup(&tasklet_runner);
 166         lockmgr(&tasklet_lock, LK_RELEASE);
 167 }
 168
 169 void
 170 tasklet_kill(struct tasklet_struct *t)
 171 {
 172         set_bit(TASKLET_IS_DYING, &t->state);
 173         wakeup(&tasklet_runner);
 174 }
 175
 176 static int init_tasklets(void *arg)
 177 {
 178         kthread_create(tasklet_runner, NULL, &tasklet_td, "tasklet_runner");
 179
 180         return 0;
 181 }
 182
 183 SYSINIT(linux_tasklet_init, SI_SUB_DRIVERS, SI_ORDER_MIDDLE, init_tasklets, NULL);