1 files changed, 204 insertions, 0 deletions
diff --git a/drivers/staging/unisys/visorbus/periodic_work.c b/drivers/staging/unisys/visorbus/periodic_work.c
new file mode 100644
index 000000000000..5e56088cf855
--- /dev/null
+++ b/drivers/staging/unisys/visorbus/periodic_work.c
@@ -0,0 +1,204 @@
+/* periodic_work.c
+ *
+ * Copyright (C) 2010 - 2013 UNISYS CORPORATION
+ * All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or (at
+ * your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
+ * NON INFRINGEMENT.  See the GNU General Public License for more
+ * details.
+ */
+
+/*
+ *  Helper functions to schedule periodic work in Linux kernel mode.
+ */
+#include <linux/sched.h>
+
+#include "periodic_work.h"
+
+#define MYDRVNAME "periodic_work"
+
+struct periodic_work {
+	rwlock_t lock;
+	struct delayed_work work;
+	void (*workfunc)(void *);
+	void *workfuncarg;
+	bool is_scheduled;
+	bool want_to_stop;
+	ulong jiffy_interval;
+	struct workqueue_struct *workqueue;
+	const char *devnam;
+};
+
+static void periodic_work_func(struct work_struct *work)
+{
+	struct periodic_work *pw;
+
+	pw = container_of(work, struct periodic_work, work.work);
+	(*pw->workfunc)(pw->workfuncarg);
+}
+
+struct periodic_work *visor_periodic_work_create(ulong jiffy_interval,
+					struct workqueue_struct *workqueue,
+					void (*workfunc)(void *),
+					void *workfuncarg,
+					const char *devnam)
+{
+	struct periodic_work *pw;
+
+	pw = kzalloc(sizeof(*pw), GFP_KERNEL | __GFP_NORETRY);
+	if (!pw)
+		return NULL;
+
+	rwlock_init(&pw->lock);
+	pw->jiffy_interval = jiffy_interval;
+	pw->workqueue = workqueue;
+	pw->workfunc = workfunc;
+	pw->workfuncarg = workfuncarg;
+	pw->devnam = devnam;
+	return pw;
+}
+EXPORT_SYMBOL_GPL(visor_periodic_work_create);
+
+void visor_periodic_work_destroy(struct periodic_work *pw)
+{
+	kfree(pw);
+}
+EXPORT_SYMBOL_GPL(visor_periodic_work_destroy);
+
+/** Call this from your periodic work worker function to schedule the next
+ *  call.
+ *  If this function returns false, there was a failure and the
+ *  periodic work is no longer scheduled
+ */
+bool visor_periodic_work_nextperiod(struct periodic_work *pw)
+{
+	bool rc = false;
+
+	write_lock(&pw->lock);
+	if (pw->want_to_stop) {
+		pw->is_scheduled = false;
+		pw->want_to_stop = false;
+		rc = true;  /* yes, true; see visor_periodic_work_stop() */
+		goto unlock;
+	} else if (queue_delayed_work(pw->workqueue, &pw->work,
+				      pw->jiffy_interval) < 0) {
+		pw->is_scheduled = false;
+		rc = false;
+		goto unlock;
+	}
+	rc = true;
+unlock:
+	write_unlock(&pw->lock);
+	return rc;
+}
+EXPORT_SYMBOL_GPL(visor_periodic_work_nextperiod);
+
+/** This function returns true iff new periodic work was actually started.
+ *  If this function returns false, then no work was started
+ *  (either because it was already started, or because of a failure).
+ */
+bool visor_periodic_work_start(struct periodic_work *pw)
+{
+	bool rc = false;
+
+	write_lock(&pw->lock);
+	if (pw->is_scheduled) {
+		rc = false;
+		goto unlock;
+	}
+	if (pw->want_to_stop) {
+		rc = false;
+		goto unlock;
+	}
+	INIT_DELAYED_WORK(&pw->work, &periodic_work_func);
+	if (queue_delayed_work(pw->workqueue, &pw->work,
+			       pw->jiffy_interval) < 0) {
+		rc = false;
+		goto unlock;
+	}
+	pw->is_scheduled = true;
+	rc = true;
+unlock:
+	write_unlock(&pw->lock);
+	return rc;
+}
+EXPORT_SYMBOL_GPL(visor_periodic_work_start);
+
+/** This function returns true iff your call actually stopped the periodic
+ *  work.
+ *
+ *  -- PAY ATTENTION... this is important --
+ *
+ *  NO NO #1
+ *
+ *     Do NOT call this function from some function that is running on the
+ *     same workqueue as the work you are trying to stop might be running
+ *     on!  If you violate this rule, visor_periodic_work_stop() MIGHT work,
+ *     but it also MIGHT get hung up in an infinite loop saying
+ *     "waiting for delayed work...".  This will happen if the delayed work
+ *     you are trying to cancel has been put in the workqueue list, but can't
+ *     run yet because we are running that same workqueue thread right now.
+ *
+ *     Bottom line: If you need to call visor_periodic_work_stop() from a
+ *     workitem, be sure the workitem is on a DIFFERENT workqueue than the
+ *     workitem that you are trying to cancel.
+ *
+ *     If I could figure out some way to check for this "no no" condition in
+ *     the code, I would.  It would have saved me the trouble of writing this
+ *     long comment.  And also, don't think this is some "theoretical" race
+ *     condition.  It is REAL, as I have spent the day chasing it.
+ *
+ *  NO NO #2
+ *
+ *     Take close note of the locks that you own when you call this function.
+ *     You must NOT own any locks that are needed by the periodic work
+ *     function that is currently installed.  If you DO, a deadlock may result,
+ *     because stopping the periodic work often involves waiting for the last
+ *     iteration of the periodic work function to complete.  Again, if you hit
+ *     this deadlock, you will get hung up in an infinite loop saying
+ *     "waiting for delayed work...".
+ */
+bool visor_periodic_work_stop(struct periodic_work *pw)
+{
+	bool stopped_something = false;
+
+	write_lock(&pw->lock);
+	stopped_something = pw->is_scheduled && (!pw->want_to_stop);
+	while (pw->is_scheduled) {
+		pw->want_to_stop = true;
+		if (cancel_delayed_work(&pw->work)) {
+			/* We get here if the delayed work was pending as
+			 * delayed work, but was NOT run.
+			 */
+			WARN_ON(!pw->is_scheduled);
+			pw->is_scheduled = false;
+		} else {
+			/* If we get here, either the delayed work:
+			 * - was run, OR,
+			 * - is running RIGHT NOW on another processor, OR,
+			 * - wasn't even scheduled (there is a miniscule
+			 *   timing window where this could be the case)
+			 * flush_workqueue() would make sure it is finished
+			 * executing, but that still isn't very useful, which
+			 * explains the loop...
+			 */
+		}
+		if (pw->is_scheduled) {
+			write_unlock(&pw->lock);
+			schedule_timeout_interruptible(msecs_to_jiffies(10));
+			write_lock(&pw->lock);
+		} else {
+			pw->want_to_stop = false;
+		}
+	}
+	write_unlock(&pw->lock);
+	return stopped_something;
+}
+EXPORT_SYMBOL_GPL(visor_periodic_work_stop);