Add a nordy sysfs attribute to suppress raising the modem-control lines on open to signal DTE readiness.
This can be use to prevent undesirable side-effects on open for applications where the DTR and RTS lines are used for non-standard purposes such as generating power-on and reset pulses. Signed-off-by: Johan Hovold <[email protected]> --- Documentation/ABI/testing/sysfs-tty | 7 +++++++ drivers/tty/serial/serial_core.c | 29 +++++++++++++++++++++++++++++ 2 files changed, 36 insertions(+) diff --git a/Documentation/ABI/testing/sysfs-tty b/Documentation/ABI/testing/sysfs-tty index e157130a6792..2634b4bf9c7f 100644 --- a/Documentation/ABI/testing/sysfs-tty +++ b/Documentation/ABI/testing/sysfs-tty @@ -161,3 +161,10 @@ Contact: Andy Shevchenko <[email protected]> Description: Allows user to detach or attach back the given device as kernel console. It shows and accepts a boolean variable. + +What: /sys/class/tty/ttyS0/nordy +Date: November 2020 +Contact: Johan Hovold <[email protected]> +Description: + Show and store the port NORDY flag which suppresses raising + the modem-control lines on open to signal DTE readiness. diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c index f41cba10b86b..063a617182ce 100644 --- a/drivers/tty/serial/serial_core.c +++ b/drivers/tty/serial/serial_core.c @@ -2805,6 +2805,33 @@ static ssize_t console_store(struct device *dev, return ret < 0 ? ret : count; } +static ssize_t nordy_show(struct device *dev, struct device_attribute *attr, + char *buf) +{ + struct tty_port *port = dev_get_drvdata(dev); + + return sprintf(buf, "%d\n", tty_port_nordy(port)); +} + +static ssize_t nordy_store(struct device *dev, struct device_attribute *attr, + const char *buf, size_t count) +{ + struct tty_port *port = dev_get_drvdata(dev); + unsigned int val; + int ret; + + ret = kstrtouint(buf, 0, &val); + if (ret) + return ret; + + if (val > 1) + return -EINVAL; + + tty_port_set_nordy(port, val); + + return count; +} + static DEVICE_ATTR_RO(uartclk); static DEVICE_ATTR_RO(type); static DEVICE_ATTR_RO(line); @@ -2819,6 +2846,7 @@ static DEVICE_ATTR_RO(io_type); static DEVICE_ATTR_RO(iomem_base); static DEVICE_ATTR_RO(iomem_reg_shift); static DEVICE_ATTR_RW(console); +static DEVICE_ATTR_RW(nordy); static struct attribute *tty_dev_attrs[] = { &dev_attr_uartclk.attr, @@ -2835,6 +2863,7 @@ static struct attribute *tty_dev_attrs[] = { &dev_attr_iomem_base.attr, &dev_attr_iomem_reg_shift.attr, &dev_attr_console.attr, + &dev_attr_nordy.attr, NULL }; -- 2.26.2
