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 /*
  58  * Linux does:
  59  * 1 - copy list locally
  60  * 2 - empty global list
  61  * 3 - process local list from head to tail
  62  *****
  63  * local list processing:
  64  * - if element cannot be run, put it at the tail
  65  * - last element == null
  66  */
  67 #define PROCESS_TASKLET_LIST(which_list) do { \
  68         STAILQ_FOREACH_MUTABLE(te, &which_list, tasklet_entries, tmp_te) { \
  69                 struct tasklet_struct *t = te->ts;                      \
  70                                                                         \
  71                 /*                                                      \
  72                    This tasklet is dying, remove it from the list.      \
  73                    We allow to it to run one last time if it has        \
  74                    already been scheduled.                              \
  75                 */                                                      \
  76                 if (test_bit(TASKLET_IS_DYING, &t->state)) {            \
  77                         STAILQ_REMOVE(&which_list, te, tasklet_entry, tasklet_entries); \
  78                         kfree(te);                                      \
  79                 }                                                       \
  80                                                                         \
  81                 /* This tasklet is not enabled, try the next one */     \
  82                 if (atomic_read(&t->count) != 0)                        \
  83                         continue;                                       \
  84                                                                         \
  85                 /* This tasklet is not scheduled, try the next one */   \
  86                 if (!test_bit(TASKLET_STATE_SCHED, &t->state))          \
  87                         continue;                                       \
  88                                                                         \
  89                 clear_bit(TASKLET_STATE_SCHED, &t->state);              \
  90                 set_bit(TASKLET_STATE_RUN, &t->state);                  \
  91                                                                         \
  92                 lockmgr(&tasklet_lock, LK_RELEASE);                     \
  93                 if (t->func)                                            \
  94                         t->func(t->data);                               \
  95                 lockmgr(&tasklet_lock, LK_EXCLUSIVE);                   \
  96                                                                         \
  97                 clear_bit(TASKLET_STATE_RUN, &t->state);                \
  98         }                                                               \
  99 } while (0)
 100
 101 /* XXX runners should be CPU-specific */
 102 static void
 103 tasklet_runner(void *arg)
 104 {
 105         struct tasklet_entry *te, *tmp_te;
 106
 107         lockmgr(&tasklet_lock, LK_EXCLUSIVE);
 108         while (1) {
 109                 /*
 110                    Only sleep if we haven't been raced by a _schedule()
 111                    call during an unlock window
 112                 */
 113                 if (tasklet_pending == 0) {
 114                         lksleep(&tasklet_runner, &tasklet_lock, 0, "tkidle", 0);
 115                 }
 116                 tasklet_pending = 0;
 117
 118                 /* Process hi tasklets first */
 119                 PROCESS_TASKLET_LIST(tlist_hi);
 120                 PROCESS_TASKLET_LIST(tlist);
 121         }
 122         lockmgr(&tasklet_lock, LK_RELEASE);
 123 }
 124
 125 void
 126 tasklet_init(struct tasklet_struct *t,
 127              void (*func)(unsigned long), unsigned long data)
 128 {
 129         t->state = 0;
 130         t->func = func;
 131         t->data = data;
 132         atomic_set(&t->count, 0);
 133 }
 134
 135 #define TASKLET_SCHEDULE_COMMON(t, list) do {                   \
 136         struct tasklet_entry *te;                               \
 137                                                                 \
 138         lockmgr(&tasklet_lock, LK_EXCLUSIVE);                   \
 139         set_bit(TASKLET_STATE_SCHED, &t->state);                \
 140                                                                 \
 141         STAILQ_FOREACH(te, &(list), tasklet_entries) {          \
 142                 if (te->ts == t)                                \
 143                         goto found_and_done;                    \
 144         }                                                       \
 145                                                                 \
 146         te = kzalloc(sizeof(struct tasklet_entry), M_WAITOK);   \
 147         te->ts = t;                                             \
 148         STAILQ_INSERT_TAIL(&(list), te, tasklet_entries);       \
 149                                                                 \
 150 found_and_done:                                                 \
 151         tasklet_pending = 1;                                    \
 152         wakeup(&tasklet_runner);                                \
 153         lockmgr(&tasklet_lock, LK_RELEASE);                     \
 154 } while (0)
 155
 156 void
 157 tasklet_schedule(struct tasklet_struct *t)
 158 {
 159         TASKLET_SCHEDULE_COMMON(t, tlist);
 160 }
 161
 162 void
 163 tasklet_hi_schedule(struct tasklet_struct *t)
 164 {
 165         TASKLET_SCHEDULE_COMMON(t, tlist_hi);
 166 }
 167
 168 void
 169 tasklet_kill(struct tasklet_struct *t)
 170 {
 171         set_bit(TASKLET_IS_DYING, &t->state);
 172         wakeup(&tasklet_runner);
 173 }
 174
 175 static int init_tasklets(void *arg)
 176 {
 177         kthread_create(tasklet_runner, NULL, &tasklet_td, "tasklet_runner");
 178
 179         return 0;
 180 }
 181
 182 SYSINIT(linux_tasklet_init, SI_SUB_DRIVERS, SI_ORDER_MIDDLE, init_tasklets, NULL);