[PATCH v6 2/3] serial: core: fix baud rate fallback in uart_get_baud_rate()

[Hui Peng <benquike@gmail.com>]

In uart_get_baud_rate(), when a custom divisor is requested, if
port->uartclk is zero, the fallback logic evaluates baud = port->uartclk / 16
which results in baud = 0, causing a divide-by-zero error in subsequent
calculations.

Ensure uart_get_baud_rate() falls back to a valid default baud rate when
port->uartclk is zero.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Assisted-by: LLM
Signed-off-by: Hui Peng <benquike@gmail.com>
---
 drivers/tty/serial/serial_core.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index 95774b0f1484..55bb1eaa27e7 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -480,6 +480,11 @@ uart_get_baud_rate(struct uart_port *port, struct ktermios *termios,
 		return 0;

 	max = port->uartclk / 16;
+	if (!max)
+		max = 115200;
+
 	if (termios) {
 		baud = tty_termios_baud_rate(termios);