From: David Woodhouse 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(). Signed-off-by: David Woodhouse Acked-by: Alan Cox Cc: Russell King Cc: Mariusz Kozlowski Signed-off-by: Andrew Morton --- drivers/serial/serial_core.c | 7 +++++-- 1 files changed, 5 insertions(+), 2 deletions(-) diff -puN drivers/serial/serial_core.c~dont-optimise-away-baud-rate-changes-when-bother-is-used drivers/serial/serial_core.c --- a/drivers/serial/serial_core.c~dont-optimise-away-baud-rate-changes-when-bother-is-used +++ a/drivers/serial/serial_core.c @@ -1146,11 +1146,14 @@ static void uart_set_termios(struct tty_ /* * 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 */ #define RELEVANT_IFLAG(iflag) ((iflag) & (IGNBRK|BRKINT|IGNPAR|PARMRK|INPCK)) - 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) return; _