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         STAILQ_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 STAILQ_HEAD(tasklet_list_head, tasklet_entry) tlist = STAILQ_HEAD_INITIALIZER(tlist);
  53 STAILQ_HEAD(tasklet_hi_list_head, tasklet_entry) tlist_hi = STAILQ_HEAD_INITIALIZER(tlist_hi);
  54
  55 static int tasklet_pending = 0;
  56
  57 #define PROCESS_TASKLET_LIST(which_list) do { \
  58         STAILQ_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                         STAILQ_REMOVE(&which_list, te, tasklet_entry, tasklet_entries); \
  68                         kfree(te);                                      \
  69                 }                                                       \
  70                                                                         \
  71                 /* This tasklet is not enabled, try the next one */     \
  72                 if (atomic_read(&t->count) != 0)                        \
  73                         continue;                                       \
  74                                                                         \
  75                 /* This tasklet is not scheduled, try the next one */   \
  76                 if (!test_bit(TASKLET_STATE_SCHED, &t->state))          \
  77                         continue;                                       \
  78                                                                         \
  79                 clear_bit(TASKLET_STATE_SCHED, &t->state);              \
  80                 set_bit(TASKLET_STATE_RUN, &t->state);                  \
  81                                                                         \
  82                 lockmgr(&tasklet_lock, LK_RELEASE);                     \
  83                 if (t->func)                                            \
  84                         t->func(t->data);                               \
  85                 lockmgr(&tasklet_lock, LK_EXCLUSIVE);                   \
  86                                                                         \
  87                 clear_bit(TASKLET_STATE_RUN, &t->state);                \
  88         }                                                               \
  89 } while (0)
  90
  91 /* XXX runners should be CPU-specific */
  92 static void
  93 tasklet_runner(void *arg)
  94 {
  95         struct tasklet_entry *te, *tmp_te;
  96
  97         lockmgr(&tasklet_lock, LK_EXCLUSIVE);
  98         while (1) {
  99                 /*
 100                    Only sleep if we haven't been raced by a _schedule()
 101                    call during an unlock window
 102                 */
 103                 if (tasklet_pending == 0) {
 104                         lksleep(&tasklet_runner, &tasklet_lock, 0, "tkidle", 0);
 105                 }
 106                 tasklet_pending = 0;
 107
 108                 /* Process hi tasklets first */
 109                 PROCESS_TASKLET_LIST(tlist_hi);
 110                 PROCESS_TASKLET_LIST(tlist);
 111         }
 112         lockmgr(&tasklet_lock, LK_RELEASE);
 113 }
 114
 115 void
 116 tasklet_init(struct tasklet_struct *t,
 117              void (*func)(unsigned long), unsigned long data)
 118 {
 119         t->state = 0;
 120         t->func = func;
 121         t->data = data;
 122         atomic_set(&t->count, 0);
 123 }
 124
 125 #define TASKLET_SCHEDULE_COMMON(t, list) do {                   \
 126         struct tasklet_entry *te;                               \
 127                                                                 \
 128         lockmgr(&tasklet_lock, LK_EXCLUSIVE);                   \
 129         set_bit(TASKLET_STATE_SCHED, &t->state);                \
 130                                                                 \
 131         STAILQ_FOREACH(te, &(list), tasklet_entries) {          \
 132                 if (te->ts == t)                                \
 133                         goto found_and_done;                    \
 134         }                                                       \
 135                                                                 \
 136         te = kzalloc(sizeof(struct tasklet_entry), M_WAITOK);   \
 137         te->ts = t;                                             \
 138         STAILQ_INSERT_TAIL(&(list), te, tasklet_entries);       \
 139                                                                 \
 140 found_and_done:                                                 \
 141         tasklet_pending = 1;                                    \
 142         wakeup(&tasklet_runner);                                \
 143         lockmgr(&tasklet_lock, LK_RELEASE);                     \
 144 } while (0)
 145
 146 void
 147 tasklet_schedule(struct tasklet_struct *t)
 148 {
 149         TASKLET_SCHEDULE_COMMON(t, tlist);
 150 }
 151
 152 void
 153 tasklet_hi_schedule(struct tasklet_struct *t)
 154 {
 155         TASKLET_SCHEDULE_COMMON(t, tlist_hi);
 156 }
 157
 158 void
 159 tasklet_kill(struct tasklet_struct *t)
 160 {
 161         set_bit(TASKLET_IS_DYING, &t->state);
 162         wakeup(&tasklet_runner);
 163 }
 164
 165 static int init_tasklets(void *arg)
 166 {
 167         kthread_create(tasklet_runner, NULL, &tasklet_td, "tasklet_runner");
 168
 169         return 0;
 170 }
 171
 172 SYSINIT(linux_tasklet_init, SI_SUB_DRIVERS, SI_ORDER_MIDDLE, init_tasklets, NULL);