linux-kernel - Re: [PATCH 1/3] tty: omap-serial: prevent division by zero

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Date:	Tue, 29 Jul 2014 17:00:14 +0200
From:	Frans Klaver <frans.klaver@...ns.com>
To:	<linux-serial@...r.kernel.org>
CC:	Rob Herring <robh+dt@...nel.org>, Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.cz>, <devicetree@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] tty: omap-serial: prevent division by zero

Sorry, missed some CC's in git send-email.

On Tue, Jul 29, 2014 at 04:52:55PM +0200, Frans Klaver wrote:
> If the chosen baud rate is large enough (e.g. 3.5 megabaud), the
> calculated n13 and n16 values in serial_omap_baud_is_mode16 may become
> 0. This causes a division by zero when calculating the difference
> between calculated and desired baud rates. To prevent this, cap n13 and
> n16 on 1.
> 
> Signed-off-by: Frans Klaver <frans.klaver@...ns.com>
> ---
>  drivers/tty/serial/omap-serial.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/tty/serial/omap-serial.c b/drivers/tty/serial/omap-serial.c
> index d017cec..e454b7c 100644
> --- a/drivers/tty/serial/omap-serial.c
> +++ b/drivers/tty/serial/omap-serial.c
> @@ -254,8 +254,16 @@ serial_omap_baud_is_mode16(struct uart_port *port, unsigned int baud)
>  {
>  	unsigned int n13 = port->uartclk / (13 * baud);
>  	unsigned int n16 = port->uartclk / (16 * baud);
> -	int baudAbsDiff13 = baud - (port->uartclk / (13 * n13));
> -	int baudAbsDiff16 = baud - (port->uartclk / (16 * n16));
> +	int baudAbsDiff13;
> +	int baudAbsDiff16;
> +
> +	if (n13 == 0)
> +		n13 = 1;
> +	if (n16 == 0)
> +		n16 = 1;
> +
> +	baudAbsDiff13 = baud - (port->uartclk / (13 * n13));
> +	baudAbsDiff16 = baud - (port->uartclk / (16 * n16));
>  	if (baudAbsDiff13 < 0)
>  		baudAbsDiff13 = -baudAbsDiff13;
>  	if (baudAbsDiff16 < 0)
> -- 
> 1.9.3
> 
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