Re: [PATCH v2 1/2] serial: sh-sci: Avoid divide-by-zero fault

[Hugo Villeneuve]

Hi Biju,

On Wed,  8 Apr 2026 15:20:58 +0100
Biju <biju.das.au@xxxxxxxxx> wrote:

> From: Biju Das <biju.das.jz@xxxxxxxxxxxxxx>
> 
> uart_update_timeout() computes a timeout value by dividing by the baud
> rate. If baud is zero — which can occur when the hardware returns an
> unsupported or invalid rate — this results in a divide-by-zero fault.

baud is returned by uart_get_baud_rate(), so this is not returned
by the hardware?


> 
> Signed-off-by: Biju Das <biju.das.jz@xxxxxxxxxxxxxx>

Missing Fixes tag?


> ---
> v2:
>  * New patch
> ---
>  drivers/tty/serial/rsci.c   | 3 ++-
>  drivers/tty/serial/sh-sci.c | 3 ++-
>  2 files changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/tty/serial/rsci.c b/drivers/tty/serial/rsci.c
> index b00c9e385169..a0858bab0822 100644
> --- a/drivers/tty/serial/rsci.c
> +++ b/drivers/tty/serial/rsci.c
> @@ -286,7 +286,8 @@ static void rsci_set_termios(struct uart_port *port, struct ktermios *termios,
>  	sci_port_enable(s);
>  	uart_port_lock_irqsave(port, &flags);
>  
> -	uart_update_timeout(port, termios->c_cflag, baud);
> +	if (baud)
> +		uart_update_timeout(port, termios->c_cflag, baud);
>  
>  	rsci_serial_out(port, CCR0, ccr0_val);
>  
> diff --git a/drivers/tty/serial/sh-sci.c b/drivers/tty/serial/sh-sci.c
> index 6c819b6b2425..429e89106ee3 100644
> --- a/drivers/tty/serial/sh-sci.c
> +++ b/drivers/tty/serial/sh-sci.c
> @@ -2805,7 +2805,8 @@ static void sci_set_termios(struct uart_port *port, struct ktermios *termios,
>  
>  	sci_reset(port);
>  
> -	uart_update_timeout(port, termios->c_cflag, baud);
> +	if (baud)
> +		uart_update_timeout(port, termios->c_cflag, baud);

After this patch, have you re-tested if having baud = 0 produces any
other errors? A litle bit later in the same function, there is this
code:

    /* Calculate delay for 2 DMA buffers (4 FIFO). */
    s->rx_frame = (10000 * bits) / (baud / 100);

Does this trigger a division by zero fault?

There is also this:

	if ((srr + 1 == 5) &&
	    (s->type == PORT_SCIFA || s->type == PORT_SCIFB)) {
            ...
		udelay(DIV_ROUND_UP(10 * 1000000, baud));

Can this also trigger a division by zero fault?


>  
>  	/* byte size and parity */
>  	bits = tty_get_frame_size(termios->c_cflag);
> -- 
> 2.43.0
> 
> 


-- 
Hugo Villeneuve