serial: core: tidy invalid baudrate handling in uart_get_baud_rate

uart_get_baud_rate has input parameters 'min' and 'max' limiting the
range of acceptable baud rates from the caller's perspective. If neither
current or old termios structures have acceptable baud rate setting and
9600 is not in the min/max range either the function returns 0 and
issues a warning.
However for a UART that does not support speed of 9600 baud this is
expected behavior.
Clarify that 0 can be (and always could be) returned from the
uart_get_baud_rate. Don't issue a warning in that case.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Link: https://lore.kernel.org/r/20231010085926.1021667-2-jcmvbkbc@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index 980abb44cf82d9225d0cac2b53f3ef62a248a8d2..b106eb3943d073107ada9652c1f53fda46b9ea04 100644 (file)
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -431,7 +431,7 @@ EXPORT_SYMBOL(uart_update_timeout);
  * baud.
  *
  * If the new baud rate is invalid, try the @old termios setting. If it's still
- * invalid, we try 9600 baud.
+ * invalid, we try 9600 baud. If that is also invalid 0 is returned.
  *
  * The @termios structure is updated to reflect the baud rate we're actually
  * going to be using. Don't do this for the case where B0 is requested ("hang
@@ -515,8 +515,6 @@ uart_get_baud_rate(struct uart_port *port, struct ktermios *termios,
                                                        max - 1, max - 1);
                }
        }
-       /* Should never happen */
-       WARN_ON(1);
        return 0;
 }
 EXPORT_SYMBOL(uart_get_baud_rate);