+
+#ifdef CONFIG_PREEMPT_RT_BASE
+ #define SYSVSEM_COMPLETION 1
+#else
+ #define SYSVSEM_CUSTOM 1
+#endif
+
+#ifdef SYSVSEM_COMPLETION
+ /* Using a completion causes some overhead, but avoids a busy loop
+ * that increases the worst case latency.
+ */
+ struct queue_done {
+ struct completion done;
+ };
+
+ static void queuewakeup_prepare(void)
+ {
+ /* no preparation necessary */
+ }
+
+ static void queuewakeup_completed(void)
+ {
+ /* empty */
+ }
+
+ static void queuewakeup_block(struct queue_done *qd)
+ {
+ /* empty */
+ }
+
+ static void queuewakeup_handsoff(struct queue_done *qd)
+ {
+ complete_all(&qd->done);
+ }
+
+ static void queuewakeup_init(struct queue_done *qd)
+ {
+ init_completion(&qd->done);
+ }
+
+ static void queuewakeup_wait(struct queue_done *qd)
+ {
+ wait_for_completion(&qd->done);
+ }
+
+#elif defined(SYSVSEM_SPINLOCK)
+ /* Note: Spinlocks do not work because:
+ * - lockdep complains [could be fixed]
+ * - only 255 concurrent spin_lock() calls are permitted, then the
+ * preempt-counter overflows
+ */
+#error SYSVSEM_SPINLOCK is a prove of concept, does not work.
+ struct queue_done {
+ spinlock_t done;
+ };
+
+ static void queuewakeup_prepare(void)
+ {
+ /* empty */
+ }
+
+ static void queuewakeup_completed(void)
+ {
+ /* empty */
+ }
+
+ static void queuewakeup_block(struct queue_done *qd)
+ {
+ BUG_ON(spin_is_locked(&qd->done));
+ spin_lock(&qd->done);
+ }
+
+ static void queuewakeup_handsoff(struct queue_done *qd)
+ {
+ spin_unlock(&qd->done);
+ }
+
+ static void queuewakeup_init(struct queue_done *qd)
+ {
+ spin_lock_init(&qd->done);
+ }
+
+ static void queuewakeup_wait(struct queue_done *qd)
+ {
+ spin_unlock_wait(&qd->done);
+ }
+#else
+ struct queue_done {
+ atomic_t done;
+ };
+
+ static void queuewakeup_prepare(void)
+ {
+ preempt_disable();
+ }
+
+ static void queuewakeup_completed(void)
+ {
+ preempt_enable();
+ }
+
+ static void queuewakeup_block(struct queue_done *qd)
+ {
+ BUG_ON(atomic_read(&qd->done) != 1);
+ atomic_set(&qd->done, 2);
+ }
+
+ static void queuewakeup_handsoff(struct queue_done *qd)
+ {
+ BUG_ON(atomic_read(&qd->done) != 2);
+ smp_mb();
+ atomic_set(&qd->done, 1);
+ }
+
+ static void queuewakeup_init(struct queue_done *qd)
+ {
+ atomic_set(&qd->done, 1);
+ }
+
+ static void queuewakeup_wait(struct queue_done *qd)
+ {
+ while (atomic_read(&qd->done) != 1)
+ cpu_relax();
+
+ smp_mb();
+ }
+#endif
+
+