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
