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    Subject[SERIAL] Don't optimise away baud rate changes when BOTHER is used (v2)
    The uart_set_termios() function will bail out early without bothering to
    touch the hardware, if it decides that nothing "relevant" has changed.
    Unfortunately, its idea of "relevant" doesn't include c_[io]speed. So if
    the baud rate bits are BOTHER and you just change the speed, the change
    gets optimised away.

    This patch makes it ignore the old Bfoo bits in c_cflag and just check
    whether c_ispeed and c_ospeed have changed. Those integers are always
    set appropriately for us by set_termios().

    This version of the patch lacks the debugging printk which I
    accidentally left in the previous one.

    Signed-off-by: David Woodhouse <>

    diff --git a/drivers/serial/serial_core.c b/drivers/serial/serial_core.c
    index e8be3b5..4480990 100644
    --- a/drivers/serial/serial_core.c
    +++ b/drivers/serial/serial_core.c
    @@ -1146,11 +1146,19 @@ static void uart_set_termios(struct tty_struct *tty, struct ktermios *old_termio

    * These are the bits that are used to setup various
    - * flags in the low level driver.
    + * flags in the low level driver. We can ignore the Bfoo
    + * bits in c_cflag; c_[io]speed will always be set
    + * appropriately by set_termios() in tty_ioctl.c
    +#ifdef CIBAUD
    +#define RELEVANT_CFLAG(cflag) ((cflag) & ~(CIBAUD|CBAUD)
    +#define RELEVANT_CFLAG(cflag) ((cflag) & ~(CIBAUD|CBAUD)
    if ((cflag ^ old_termios->c_cflag) == 0 &&
    + tty->termios->c_ospeed == old_termios->c_ospeed &&
    + tty->termios->c_ispeed == old_termios->c_ispeed &&
    RELEVANT_IFLAG(tty->termios->c_iflag ^ old_termios->c_iflag) == 0)


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      Last update: 2007-06-08 13:17    [W:0.025 / U:23.148 seconds]
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