[U-Boot-Users] [PATCH V2] Round the serial port clock divisor value returned by calc_divisor()

Wolfgang Denk
2008-07-10T22:39:16Z

In message <1215543298-26921-1-git-send-email-hugo.villeneuve@lyrtech.com> you wrote:
> Round the serial port clock divisor value returned by
> calc_divisor().
>
> Signed-off-by: Hugo Villeneuve <hugo.villeneuve@lyrtech.com>
> Signed-off-by: John Roberts <john.roberts@pwav.com>
>
> ---
>
> Rounding is important, especially when using high baud rates
> values like 115200bps. When using the non-rounded value, some
> boards will work and some won't.
>
> drivers/serial/serial.c | 6 +++++-
> 1 files changed, 5 insertions(+), 1 deletions(-)
>
> diff --git a/drivers/serial/serial.c b/drivers/serial/serial.c
> index 76425d8..1192f07 100644
> --- a/drivers/serial/serial.c
> +++ b/drivers/serial/serial.c
> @@ -144,8 +144,12 @@ static int calc_divisor (NS16550_t port)
> #else
> #define MODE_X_DIV 16
> #endif
> - return (CFG_NS16550_CLK / MODE_X_DIV / gd->baudrate);
>
> + /* Compute divisor value. Normally, we should simply return:
> + * CFG_NS16550_CLK) / MODE_X_DIV / gd->baudrate
> + * but we need to round that value by adding 0.5 or 8/16.
> + * Rounding is especially important at high baud rates. */
> + return (((16 * CFG_NS16550_CLK) / MODE_X_DIV / gd->baudrate) + 8) / 16;
> }

Your patch causes problems with some boards:

Configuring for SBC8540 board...
serial.c: In function 'calc_divisor':
serial.c:153: warning: integer overflow in expression
serial.c:153: warning: integer overflow in expression

Configuring for sbc8548 board...
serial.c: In function 'calc_divisor':
serial.c:153: warning: integer overflow in expression
serial.c:153: warning: integer overflow in expression

Do you have a quick fix, or shall I back out the patch?

Best regards,

Wolfgang Denk

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