There exist special serial devices (either attaching to generic serial ports or containing a built-in USB-serial chip) in which DTR and/or RTS have been repurposed for non-standard uses. Depending on exactly how these signals are repurposed, standard POSIX/SUS behaviour of unconditionally raising both signals on open may range from harmless to undesirable to a total killer, precluding the use of Linux with such custom hardware. The newly added TTY_PORT_MANUAL_RTSDTR flag switches an individual serial port from POSIX/SUS standard to non-standard behaviour: when set, it suppresses the built-in action of raising DTR & RTS on serial port open. This flag can be exported through sysfs, and it can also be set by USB-serial device drivers when they see a custom hw device (identified by VID:PID) that is known to be wired in a way that requires this flag to be set. Co-developed-by: Johan Hovold <johan@xxxxxxxxxx> Signed-off-by: Johan Hovold <johan@xxxxxxxxxx> Signed-off-by: Mychaela N. Falconia <falcon@xxxxxxxxxxxxxxx> --- drivers/tty/tty_port.c | 2 +- include/linux/tty_port.h | 11 +++++++++++ 2 files changed, 12 insertions(+), 1 deletion(-) diff --git a/drivers/tty/tty_port.c b/drivers/tty/tty_port.c index 880608a65773..59f1c49bb23c 100644 --- a/drivers/tty/tty_port.c +++ b/drivers/tty/tty_port.c @@ -441,7 +441,7 @@ EXPORT_SYMBOL(tty_port_carrier_raised); */ void tty_port_raise_dtr_rts(struct tty_port *port) { - if (port->ops->dtr_rts) + if (port->ops->dtr_rts && !tty_port_manual_rtsdtr(port)) port->ops->dtr_rts(port, 1); } EXPORT_SYMBOL(tty_port_raise_dtr_rts); diff --git a/include/linux/tty_port.h b/include/linux/tty_port.h index 58e9619116b7..9e5ad46d8a53 100644 --- a/include/linux/tty_port.h +++ b/include/linux/tty_port.h @@ -133,6 +133,7 @@ struct tty_port { #define TTY_PORT_CHECK_CD 4 /* carrier detect enabled */ #define TTY_PORT_KOPENED 5 /* device exclusively opened by kernel */ +#define TTY_PORT_MANUAL_RTSDTR 6 /* do not raise DTR & RTS on open */ void tty_port_init(struct tty_port *port); void tty_port_link_device(struct tty_port *port, struct tty_driver *driver, @@ -226,6 +227,16 @@ static inline void tty_port_set_kopened(struct tty_port *port, bool val) assign_bit(TTY_PORT_KOPENED, &port->iflags, val); } +static inline bool tty_port_manual_rtsdtr(const struct tty_port *port) +{ + return test_bit(TTY_PORT_MANUAL_RTSDTR, &port->iflags); +} + +static inline void tty_port_set_manual_rtsdtr(struct tty_port *port, bool val) +{ + assign_bit(TTY_PORT_MANUAL_RTSDTR, &port->iflags, val); +} + struct tty_struct *tty_port_tty_get(struct tty_port *port); void tty_port_tty_set(struct tty_port *port, struct tty_struct *tty); int tty_port_carrier_raised(struct tty_port *port); -- 2.9.0