greybus: svc: add a "watchdog" to check the network health

Now that we have a svc ping command, let's add a watchdog to call it
every so often (1 second at the moment.)  If it finds something went
wrong, post a stern message to the kernel log and call:
	start unipro_reset
to reset the whole greybus hardware subsystem.
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Reviewed-by: Rui Miguel Silva <rui.silva@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

drivers/staging/greybus/Makefile

@@ -8,6 +8,7 @@ greybus-y :=	core.o		\
 		protocol.o	\
 		control.o	\
 		svc.o		\
+		svc_watchdog.o	\
 		firmware.o	\
 		operation.o	\
 		legacy.o

drivers/staging/greybus/svc.c

@@ -436,6 +436,13 @@ static int gb_svc_hello(struct gb_operation *op)
 		return ret;
 	}
 
+	ret = gb_svc_watchdog_create(svc);
+	if (ret) {
+		dev_err(&svc->dev, "failed to create watchdog: %d\n", ret);
+		input_unregister_device(svc->input);
+		device_del(&svc->dev);
+	}
+
 	return 0;
 }
 
@@ -963,6 +970,7 @@ void gb_svc_del(struct gb_svc *svc)
 	 * from the request handler.
 	 */
 	if (device_is_registered(&svc->dev)) {
+		gb_svc_watchdog_destroy(svc);
 		input_unregister_device(svc->input);
 		device_del(&svc->dev);
 	}

drivers/staging/greybus/svc.h

@@ -16,6 +16,8 @@ enum gb_svc_state {
 	GB_SVC_STATE_SVC_HELLO,
 };
 
+struct gb_svc_watchdog;
+
 struct gb_svc {
 	struct device		dev;
 
@@ -33,6 +35,7 @@ struct gb_svc {
 
 	struct input_dev        *input;
 	char                    *input_phys;
+	struct gb_svc_watchdog	*watchdog;
 };
 #define to_gb_svc(d) container_of(d, struct gb_svc, d)
 
@@ -56,6 +59,8 @@ int gb_svc_intf_set_power_mode(struct gb_svc *svc, u8 intf_id, u8 hs_series,
 			       u8 rx_mode, u8 rx_gear, u8 rx_nlanes,
 			       u8 flags, u32 quirks);
 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);
 
 int gb_svc_protocol_init(void);
 void gb_svc_protocol_exit(void);

drivers/staging/greybus/svc_watchdog.c

+/*
+ * SVC Greybus "watchdog" driver.
+ *
+ * Copyright 2016 Google Inc.
+ *
+ * Released under the GPLv2 only.
+ */
+
+#include <linux/delay.h>
+#include <linux/workqueue.h>
+#include "greybus.h"
+
+#define SVC_WATCHDOG_PERIOD	(2*HZ)
+
+struct gb_svc_watchdog {
+	struct delayed_work	work;
+	struct gb_svc		*svc;
+	bool			finished;
+};
+
+static struct delayed_work reset_work;
+
+static void greybus_reset(struct work_struct *work)
+{
+	static char start_path[256] = "/system/bin/start";
+	static char *envp[] = {
+		"HOME=/",
+		"PATH=/sbin:/vendor/bin:/system/sbin:/system/bin:/system/xbin",
+		NULL,
+	};
+	static char *argv[] = {
+		start_path,
+		"unipro_reset",
+		NULL,
+	};
+
+	printk(KERN_ERR "svc_watchdog: calling \"%s %s\" to reset greybus network!\n",
+	       argv[0], argv[1]);
+	call_usermodehelper(start_path, argv, envp, UMH_WAIT_EXEC);
+}
+
+static void do_work(struct work_struct *work)
+{
+	struct gb_svc_watchdog *watchdog;
+	struct gb_svc *svc;
+	int retval;
+
+	watchdog = container_of(work, struct gb_svc_watchdog, work.work);
+	svc = watchdog->svc;
+
+	dev_dbg(&svc->dev, "%s: ping.\n", __func__);
+	retval = gb_svc_ping(svc);
+	if (retval) {
+		/*
+		 * Something went really wrong, let's warn userspace and then
+		 * pull the plug and reset the whole greybus network.
+		 * We need to do this outside of this workqueue as we will be
+		 * tearing down the svc device itself.  So queue up
+		 * yet-another-callback to do that.
+		 */
+		dev_err(&svc->dev,
+			"SVC ping has returned %d, something is wrong!!!\n",
+			retval);
+		dev_err(&svc->dev, "Resetting the greybus network, watch out!!!\n");
+
+		INIT_DELAYED_WORK(&reset_work, greybus_reset);
+		queue_delayed_work(system_wq, &reset_work, HZ/2);
+		return;
+	}
+
+	/* resubmit our work to happen again, if we are still "alive" */
+	if (!watchdog->finished)
+		queue_delayed_work(system_wq, &watchdog->work,
+				   SVC_WATCHDOG_PERIOD);
+}
+
+int gb_svc_watchdog_create(struct gb_svc *svc)
+{
+	struct gb_svc_watchdog *watchdog;
+
+	if (svc->watchdog)
+		return 0;
+
+	watchdog = kmalloc(sizeof(*watchdog), GFP_KERNEL);
+	if (!watchdog)
+		return -ENOMEM;
+
+	watchdog->finished = 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;
+}
+
+void gb_svc_watchdog_destroy(struct gb_svc *svc)
+{
+	struct gb_svc_watchdog *watchdog = svc->watchdog;
+
+	if (!watchdog)
+		return;
+
+	watchdog->finished = true;
+	cancel_delayed_work_sync(&watchdog->work);
+	svc->watchdog = NULL;
+	kfree(watchdog);
+}