greybus: svc watchdog: allow it to be enabled/disabled from userspace

Sometimes you want to disable the SVC watchdog without having to patch
your kernel, so provide a sysfs file to do this.  This can let us do
power measurements, and let the firmware developers not go crazy
worrying that the kernel is going to reset their chips with no notice.
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

drivers/staging/greybus/Documentation/sysfs-bus-greybus

@@ -163,3 +163,11 @@ KernelVersion:	4.XX
 Contact:	Greg Kroah-Hartman <greg@kroah.com>
 Description:
 		The version number of the firmware in the SVC device.
+
+What:		/sys/bus/greybus/device/N-svc/watchdog
+Date:		October 2016
+KernelVersion:	4.XX
+Contact:	Greg Kroah-Hartman <greg@kroah.com>
+Description:
+		If the SVC watchdog is enabled or not.  Writing 0 to this
+		file will disable the watchdog, writing 1 will enable it.

drivers/staging/greybus/svc.c

@@ -70,10 +70,42 @@ static ssize_t intf_eject_store(struct device *dev,
 }
 static DEVICE_ATTR_WO(intf_eject);
 
+static ssize_t watchdog_show(struct device *dev, struct device_attribute *attr,
+			     char *buf)
+{
+	struct gb_svc *svc = to_gb_svc(dev);
+
+	return sprintf(buf, "%s\n",
+		       gb_svc_watchdog_enabled(svc) ? "enabled" : "disabled");
+}
+
+static ssize_t watchdog_store(struct device *dev,
+			      struct device_attribute *attr, const char *buf,
+			      size_t len)
+{
+	struct gb_svc *svc = to_gb_svc(dev);
+	int retval;
+	bool user_request;
+
+	retval = strtobool(buf, &user_request);
+	if (retval)
+		return retval;
+
+	if (user_request)
+		retval = gb_svc_watchdog_enable(svc);
+	else
+		retval = gb_svc_watchdog_disable(svc);
+	if (retval)
+		return retval;
+	return len;
+}
+static DEVICE_ATTR_RW(watchdog);
+
 static struct attribute *svc_attrs[] = {
 	&dev_attr_endo_id.attr,
 	&dev_attr_ap_intf_id.attr,
 	&dev_attr_intf_eject.attr,
+	&dev_attr_watchdog.attr,
 	NULL,
 };
 ATTRIBUTE_GROUPS(svc);

drivers/staging/greybus/svc.h

@@ -61,6 +61,9 @@ int gb_svc_intf_set_power_mode(struct gb_svc *svc, u8 intf_id, u8 hs_series,
 int gb_svc_ping(struct gb_svc *svc);
 int gb_svc_watchdog_create(struct gb_svc *svc);
 void gb_svc_watchdog_destroy(struct gb_svc *svc);
+bool gb_svc_watchdog_enabled(struct gb_svc *svc);
+int gb_svc_watchdog_enable(struct gb_svc *svc);
+int gb_svc_watchdog_disable(struct gb_svc *svc);
 
 int gb_svc_protocol_init(void);
 void gb_svc_protocol_exit(void);

drivers/staging/greybus/svc_watchdog.c

@@ -15,7 +15,7 @@
 struct gb_svc_watchdog {
 	struct delayed_work	work;
 	struct gb_svc		*svc;
-	bool			finished;
+	bool			enabled;
 };
 
 static struct delayed_work reset_work;
@@ -65,11 +65,16 @@ static void do_work(struct work_struct *work)
 
 		INIT_DELAYED_WORK(&reset_work, greybus_reset);
 		queue_delayed_work(system_wq, &reset_work, HZ/2);
-		return;
+
+		/*
+		 * Disable ourselves, we don't want to trip again unless
+		 * userspace wants us to.
+		 */
+		watchdog->enabled = false;
 	}
 
 	/* resubmit our work to happen again, if we are still "alive" */
-	if (!watchdog->finished)
+	if (watchdog->enabled)
 		queue_delayed_work(system_wq, &watchdog->work,
 				   SVC_WATCHDOG_PERIOD);
 }
@@ -85,14 +90,12 @@ int gb_svc_watchdog_create(struct gb_svc *svc)
 	if (!watchdog)
 		return -ENOMEM;
 
-	watchdog->finished = false;
+	watchdog->enabled = false;
 	watchdog->svc = svc;
 	INIT_DELAYED_WORK(&watchdog->work, do_work);
 	svc->watchdog = watchdog;
 
-	queue_delayed_work(system_wq, &watchdog->work,
-			   SVC_WATCHDOG_PERIOD);
-	return 0;
+	return gb_svc_watchdog_enable(svc);
 }
 
 void gb_svc_watchdog_destroy(struct gb_svc *svc)
@@ -102,8 +105,47 @@ void gb_svc_watchdog_destroy(struct gb_svc *svc)
 	if (!watchdog)
 		return;
 
-	watchdog->finished = true;
-	cancel_delayed_work_sync(&watchdog->work);
+	gb_svc_watchdog_disable(svc);
 	svc->watchdog = NULL;
 	kfree(watchdog);
 }
+
+bool gb_svc_watchdog_enabled(struct gb_svc *svc)
+{
+	if (!svc || !svc->watchdog)
+		return false;
+	return svc->watchdog->enabled;
+}
+
+int gb_svc_watchdog_enable(struct gb_svc *svc)
+{
+	struct gb_svc_watchdog *watchdog;
+
+	if (!svc->watchdog)
+		return -ENODEV;
+
+	watchdog = svc->watchdog;
+	if (watchdog->enabled)
+		return 0;
+
+	watchdog->enabled = true;
+	queue_delayed_work(system_wq, &watchdog->work,
+			   SVC_WATCHDOG_PERIOD);
+	return 0;
+}
+
+int gb_svc_watchdog_disable(struct gb_svc *svc)
+{
+	struct gb_svc_watchdog *watchdog;
+
+	if (!svc->watchdog)
+		return -ENODEV;
+
+	watchdog = svc->watchdog;
+	if (!watchdog->enabled)
+		return 0;
+
+	watchdog->enabled = false;
+	cancel_delayed_work_sync(&watchdog->work);
+	return 0;
+}