transport: deprecate auto-selection of transport

Historically, if the user does not specify a transport, OpenOCD
select automatically the first transport listed in the adapter
driver.
This auto-selection can behave differently by changing adapter,
so the transport should be enforced in the configuration file.

Deprecate the auto-selection and print a warning message when a
transport gets auto-selected.
There are two cases:
- adapter offers one transport only. The code early auto-selects
  the transport but does not print anything. If later the user
  selects the transport then no deprecation will be printed during
  'transport init';
- user runs 'transport select', e.g. in 'swj-dp' script, and this
  triggers the auto-selection and the deprecated message.

Change-Id: I2e55b9dcc6da77ca937978fbfb36bc365b803f0d
Signed-off-by: Antonio Borneo <[email protected]>
Reviewed-on: https://review.openocd.org/c/openocd/+/8692
Reviewed-by: Jan Matyas <[email protected]>
Reviewed-by: zapb <[email protected]>
Tested-by: jenkins

Author: borneoa

src/transport/transport.c

@@ -52,6 +52,11 @@ static struct transport *transport_list;
  */
 static const char * const *allowed_transports;
 
+/**
+ * Adapter supports a single transport; it has been auto-selected
+ */
+static bool transport_single_is_autoselected;
+
 /** * The transport being used for the current OpenOCD session.  */
 static struct transport *session;
 
@@ -104,7 +109,8 @@ int allow_transports(struct command_context *ctx, const char * const *vector)
 
 	/* autoselect if there's no choice ... */
 	if (!vector[1]) {
-		LOG_INFO("only one transport option; autoselecting '%s'", vector[0]);
+		LOG_DEBUG("only one transport option; autoselecting '%s'", vector[0]);
+		transport_single_is_autoselected = true;
 		return transport_select(ctx, vector[0]);
 	}
 
@@ -182,6 +188,11 @@ COMMAND_HANDLER(handle_transport_init)
 		return ERROR_FAIL;
 	}
 
+	if (transport_single_is_autoselected)
+		LOG_WARNING("DEPRECATED: auto-selecting transport \"%s\". "
+			"Use 'transport select %s' to suppress this message.",
+			session->name, session->name);
+
 	return session->init(CMD_CTX);
 }
 
@@ -216,8 +227,9 @@ COMMAND_HANDLER(handle_transport_select)
 				command_print(CMD, "Debug adapter does not support any transports? Check config file order.");
 				return ERROR_FAIL;
 			}
-			LOG_INFO("auto-selecting first available session transport \"%s\". "
-				"To override use 'transport select <transport>'.", allowed_transports[0]);
+			LOG_WARNING("DEPRECATED: auto-selecting transport \"%s\". "
+				"Use 'transport select %s' to suppress this message.",
+				allowed_transports[0], allowed_transports[0]);
 			int retval = transport_select(CMD_CTX, allowed_transports[0]);
 			if (retval != ERROR_OK)
 				return retval;
@@ -229,6 +241,11 @@ COMMAND_HANDLER(handle_transport_select)
 	/* assign transport */
 	if (session) {
 		if (!strcmp(session->name, CMD_ARGV[0])) {
+			if (transport_single_is_autoselected) {
+				/* Nothing to do, but also nothing to complain */
+				transport_single_is_autoselected = false;
+				return ERROR_OK;
+			}
 			LOG_WARNING("Transport \"%s\" was already selected", session->name);
 			return ERROR_OK;
 		}