watchdog: Add tracing events for the most usual watchdog events

To simplify debugging which process touches a watchdog and when, add
tracing events for .start(), .set_timeout(), .ping() and .stop().

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20221008174602.3972859-1-u.kleine-koenig@pengutronix.de
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>

MAINTAINERS

@@ -21864,6 +21864,7 @@ F:	Documentation/watchdog/
 F:	drivers/watchdog/
 F:	include/linux/watchdog.h
 F:	include/uapi/linux/watchdog.h
+F:	include/trace/events/watchdog.h
 
 WHISKEYCOVE PMIC GPIO DRIVER
 M:	Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>

drivers/watchdog/watchdog_core.c

@@ -38,6 +38,9 @@
 
 #include "watchdog_core.h"	/* For watchdog_dev_register/... */
 
+#define CREATE_TRACE_POINTS
+#include <trace/events/watchdog.h>
+
 static DEFINE_IDA(watchdog_ida);
 
 static int stop_on_reboot = -1;
@@ -163,6 +166,7 @@ static int watchdog_reboot_notifier(struct notifier_block *nb,
 			int ret;
 
 			ret = wdd->ops->stop(wdd);
+			trace_watchdog_stop(wdd, ret);
 			if (ret)
 				return NOTIFY_BAD;
 		}

drivers/watchdog/watchdog_dev.c

@@ -47,6 +47,8 @@
 #include "watchdog_core.h"
 #include "watchdog_pretimeout.h"
 
+#include <trace/events/watchdog.h>
+
 /* the dev_t structure to store the dynamically allocated watchdog devices */
 static dev_t watchdog_devt;
 /* Reference to watchdog device behind /dev/watchdog */
@@ -157,10 +159,13 @@ static int __watchdog_ping(struct watchdog_device *wdd)
 
 	wd_data->last_hw_keepalive = now;
 
-	if (wdd->ops->ping)
+	if (wdd->ops->ping) {
 		err = wdd->ops->ping(wdd);  /* ping the watchdog */
-	else
+		trace_watchdog_ping(wdd, err);
+	} else {
 		err = wdd->ops->start(wdd); /* restart watchdog */
+		trace_watchdog_start(wdd, err);
+	}
 
 	if (err == 0)
 		watchdog_hrtimer_pretimeout_start(wdd);
@@ -259,6 +264,7 @@ static int watchdog_start(struct watchdog_device *wdd)
 		}
 	} else {
 		err = wdd->ops->start(wdd);
+		trace_watchdog_start(wdd, err);
 		if (err == 0) {
 			set_bit(WDOG_ACTIVE, &wdd->status);
 			wd_data->last_keepalive = started_at;
@@ -297,6 +303,7 @@ static int watchdog_stop(struct watchdog_device *wdd)
 	if (wdd->ops->stop) {
 		clear_bit(WDOG_HW_RUNNING, &wdd->status);
 		err = wdd->ops->stop(wdd);
+		trace_watchdog_stop(wdd, err);
 	} else {
 		set_bit(WDOG_HW_RUNNING, &wdd->status);
 	}
@@ -369,6 +376,7 @@ static int watchdog_set_timeout(struct watchdog_device *wdd,
 
 	if (wdd->ops->set_timeout) {
 		err = wdd->ops->set_timeout(wdd, timeout);
+		trace_watchdog_set_timeout(wdd, timeout, err);
 	} else {
 		wdd->timeout = timeout;
 		/* Disable pretimeout if it doesn't fit the new timeout */

include/trace/events/watchdog.h

@@ -0,0 +1,66 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM watchdog
+
+#if !defined(_TRACE_WATCHDOG_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_WATCHDOG_H
+
+#include <linux/watchdog.h>
+#include <linux/tracepoint.h>
+
+DECLARE_EVENT_CLASS(watchdog_template,
+
+	TP_PROTO(struct watchdog_device *wdd, int err),
+
+	TP_ARGS(wdd, err),
+
+	TP_STRUCT__entry(
+		__field(int, id)
+		__field(int, err)
+	),
+
+	TP_fast_assign(
+		__entry->id = wdd->id;
+		__entry->err = err;
+	),
+
+	TP_printk("watchdog%d err=%d", __entry->id, __entry->err)
+);
+
+DEFINE_EVENT(watchdog_template, watchdog_start,
+	TP_PROTO(struct watchdog_device *wdd, int err),
+	TP_ARGS(wdd, err));
+
+DEFINE_EVENT(watchdog_template, watchdog_ping,
+	TP_PROTO(struct watchdog_device *wdd, int err),
+	TP_ARGS(wdd, err));
+
+DEFINE_EVENT(watchdog_template, watchdog_stop,
+	TP_PROTO(struct watchdog_device *wdd, int err),
+	TP_ARGS(wdd, err));
+
+TRACE_EVENT(watchdog_set_timeout,
+
+	TP_PROTO(struct watchdog_device *wdd, unsigned int timeout, int err),
+
+	TP_ARGS(wdd, timeout, err),
+
+	TP_STRUCT__entry(
+		__field(int, id)
+		__field(unsigned int, timeout)
+		__field(int, err)
+	),
+
+	TP_fast_assign(
+		__entry->id = wdd->id;
+		__entry->timeout = timeout;
+		__entry->err = err;
+	),
+
+	TP_printk("watchdog%d timeout=%u err=%d", __entry->id, __entry->timeout, __entry->err)
+);
+
+#endif /* !defined(_TRACE_WATCHDOG_H) || defined(TRACE_HEADER_MULTI_READ) */
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>