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 <johan@xxxxxxxxxx>
---
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 <andriy.shevchenko@xxxxxxxxxxxxxxx>
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 <johan@xxxxxxxxxx>
+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
