stlink: enable connect under reset

Currently if the target supports srst_nogate we wait until target assert_reset
until we get a chance to assert the srst.
However sometimes we will not get this far if the target has already failed
the initial scan.

This has been tested on stm32.

Change-Id: I2c4486942a011534d3e2044788563669bf457b60
Signed-off-by: Spencer Oliver <spen@spen-soft.co.uk>
Reviewed-on: http://openocd.zylin.com/972
Reviewed-by: Paul Fertser <fercerpav@gmail.com>
Tested-by: jenkins
Reviewed-by: Freddie Chopin <freddie.chopin@gmail.com>

src/jtag/stlink/stlink_interface.c

@@ -43,7 +43,11 @@ int stlink_interface_open(enum stlink_transports tr)
 	/* set transport mode */
 	stlink_if.param.transport = tr;
 
-	return stlink_if.layout->open(&stlink_if);
+	int result = stlink_if.layout->open(&stlink_if);
+	if (result != ERROR_OK)
+		return result;
+
+	return stlink_interface_init_reset();
 }
 
 int stlink_interface_init_target(struct target *t)
@@ -127,6 +131,21 @@ static int stlink_interface_execute_queue(void)
 	return ERROR_OK;
 }
 
+int stlink_interface_init_reset(void)
+{
+	enum reset_types jtag_reset_config = jtag_get_reset_config();
+
+	if (jtag_reset_config & RESET_CNCT_UNDER_SRST) {
+		if (jtag_reset_config & RESET_SRST_NO_GATING) {
+			jtag_add_reset(0, 1);
+			stlink_if.layout->api->assert_srst(stlink_if.fd, 0);
+		} else
+			LOG_WARNING("\'srst_nogate\' reset_config option is required");
+	}
+
+	return ERROR_OK;
+}
+
 COMMAND_HANDLER(stlink_interface_handle_device_desc_command)
 {
 	LOG_DEBUG("stlink_interface_handle_device_desc_command");

src/jtag/stlink/stlink_interface.h

@@ -56,5 +56,6 @@ struct stlink_interface_s {
 int stlink_interface_open(enum stlink_transports tr);
 /** */
 int stlink_interface_init_target(struct target *t);
+int stlink_interface_init_reset(void);
 
 #endif

src/jtag/stlink/stlink_transport.c

@@ -39,6 +39,11 @@ COMMAND_HANDLER(stlink_transport_jtag_command)
 	return ERROR_OK;
 }
 
+COMMAND_HANDLER(stlink_transport_reset_command)
+{
+	return stlink_interface_init_reset();
+}
+
 static const struct command_registration
 stlink_transport_stlink_subcommand_handlers[] = {
 	{
@@ -71,7 +76,7 @@ stlink_transport_jtag_subcommand_handlers[] = {
 	{
 	 .name = "arp_init-reset",
 	 .mode = COMMAND_ANY,
-	 .handler = stlink_transport_jtag_command,
+	 .handler = stlink_transport_reset_command,
 	 .usage = ""
 	 },
 	{