greybus: svc: add ping command

This implements the SVC "ping" command.  It's tiny and simple, but we
need something like this in order for us to "know" if all is working
well.

Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

drivers/staging/greybus/greybus_protocols.h

@@ -782,6 +782,7 @@ struct gb_spi_transfer_response {
 #define GB_SVC_TYPE_INTF_SET_PWRM	0x10
 #define GB_SVC_TYPE_INTF_EJECT		0x11
 #define GB_SVC_TYPE_KEY_EVENT		0x12
+#define GB_SVC_TYPE_PING		0x13
 
 /*
  * SVC version request/response has the same payload as

drivers/staging/greybus/svc.c

@@ -363,6 +363,13 @@ int gb_svc_intf_set_power_mode(struct gb_svc *svc, u8 intf_id, u8 hs_series,
 }
 EXPORT_SYMBOL_GPL(gb_svc_intf_set_power_mode);
 
+int gb_svc_ping(struct gb_svc *svc)
+{
+	return gb_operation_sync(svc->connection, GB_SVC_TYPE_PING,
+				 NULL, 0, NULL, 0);
+}
+EXPORT_SYMBOL_GPL(gb_svc_ping);
+
 static int gb_svc_version_request(struct gb_operation *op)
 {
 	struct gb_connection *connection = op->connection;

drivers/staging/greybus/svc.h

@@ -55,6 +55,7 @@ int gb_svc_intf_set_power_mode(struct gb_svc *svc, u8 intf_id, u8 hs_series,
 			       u8 tx_mode, u8 tx_gear, u8 tx_nlanes,
 			       u8 rx_mode, u8 rx_gear, u8 rx_nlanes,
 			       u8 flags, u32 quirks);
+int gb_svc_ping(struct gb_svc *svc);
 
 int gb_svc_protocol_init(void);
 void gb_svc_protocol_exit(void);