[PATCH 5.10 08/18] USB: serial: f81232: fix division by zero on line-speed change

Greg Kroah-Hartman
2022-12-19T19:28:10Z

From: Johan Hovold <johan@kernel.org>

commit a08ca6ebafe615c9028c53fc4c9e6c9b2b1f2888 upstream.

The driver leaves the line speed unchanged in case a requested speed is
not supported. Make sure to handle the case where the current speed is
B0 (hangup) without dividing by zero when determining the clock source.

Fixes: 268ddb5e9b62 ("USB: serial: f81232: add high baud rate support")
Cc: stable@vger.kernel.org # 5.2
Cc: Ji-Ze Hong (Peter Hong) <hpeter@gmail.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/usb/serial/f81232.c | 12 +++++++-----
1 file changed, 7 insertions(+), 5 deletions(-)

--- a/drivers/usb/serial/f81232.c
+++ b/drivers/usb/serial/f81232.c
@@ -130,9 +130,6 @@ static u8 const clock_table[] = { F81232

static int calc_baud_divisor(speed_t baudrate, speed_t clockrate)
{
- if (!baudrate)
- return 0;
-
return DIV_ROUND_CLOSEST(clockrate, baudrate);
}

@@ -523,9 +520,14 @@ static void f81232_set_baudrate(struct t
speed_t baud_list[] = { baudrate, old_baudrate, F81232_DEF_BAUDRATE };

for (i = 0; i < ARRAY_SIZE(baud_list); ++i) {
- idx = f81232_find_clk(baud_list[i]);
+ baudrate = baud_list[i];
+ if (baudrate == 0) {
+ tty_encode_baud_rate(tty, 0, 0);
+ return;
+ }
+
+ idx = f81232_find_clk(baudrate);
if (idx >= 0) {
- baudrate = baud_list[i];
tty_encode_baud_rate(tty, baudrate, baudrate);
break;
}