greybus: Added a sysfs entry to power down the SVC

Added a sysfs entry called pwr_off. When a "1" is passed to it,
it sends a GB_SVC_TYPE_PWR_DOWN command to the SVC, powering it down
along with the switch and INA231 chips.

Testing Done: Tested on EVT1_5, works.
Signed-off-by: Georgi Dobrev <dobrev_georgi@projectara.com>

drivers/staging/greybus/greybus_protocols.h

@@ -798,6 +798,7 @@ struct gb_spi_transfer_response {
 #define GB_SVC_TYPE_INTF_EJECT			0x11
 #define GB_SVC_TYPE_KEY_EVENT			0x12
 #define GB_SVC_TYPE_PING			0x13
+#define GB_SVC_TYPE_PWR_DOWN			0x1d
 
 /*
  * SVC version request/response has the same payload as

drivers/staging/greybus/svc.c

@@ -99,11 +99,31 @@ static ssize_t watchdog_store(struct device *dev,
 }
 static DEVICE_ATTR_RW(watchdog);
 
+static ssize_t pwr_off_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_pwr_off(svc);
+	}
+	return len;
+}
+static DEVICE_ATTR_WO(pwr_off);
+
 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,
+	&dev_attr_pwr_off.attr,
 	NULL,
 };
 ATTRIBUTE_GROUPS(svc);
@@ -320,6 +340,14 @@ int gb_svc_ping(struct gb_svc *svc)
 }
 EXPORT_SYMBOL_GPL(gb_svc_ping);
 
+int gb_svc_pwr_off(struct gb_svc *svc)
+{
+	return gb_operation_sync_timeout(svc->connection, GB_SVC_TYPE_PWR_DOWN,
+					 NULL, 0, NULL, 0,
+					 GB_OPERATION_TIMEOUT_DEFAULT * 2);
+}
+EXPORT_SYMBOL_GPL(gb_svc_pwr_off);
+
 static int gb_svc_version_request(struct gb_operation *op)
 {
 	struct gb_connection *connection = op->connection;

drivers/staging/greybus/svc.h

@@ -71,6 +71,7 @@ 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_pwr_off(struct gb_svc *svc);
 
 int gb_svc_protocol_init(void);
 void gb_svc_protocol_exit(void);