[PATCH v2 2/6] serial: core: add sysfs attribute to suppress ready signalling on open

Mychaela N. Falconia
2022-05-31T04:37:33Z

From: Johan Hovold <johan@kernel.org>

Add a nordy sysfs attribute to suppress raising the modem-control lines
on open to signal DTE readiness.

This can be used 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@kernel.org>
Signed-off-by: Mychaela N. Falconia <falcon@freecalypso.org>
---
Documentation/ABI/testing/sysfs-tty | 7 +++++++
drivers/tty/serial/serial_core.c | 26 ++++++++++++++++++++++++++
2 files changed, 33 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-tty b/Documentation/ABI/testing/sysfs-tty
index 820e412d38a8..98cb5cf0af75 100644
--- a/Documentation/ABI/testing/sysfs-tty
+++ b/Documentation/ABI/testing/sysfs-tty
@@ -161,3 +161,10 @@ Contact: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
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@kernel.org>
+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 9a85b41caa0a..a17ac4efaceb 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -2870,6 +2870,30 @@ 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);
+ bool val;
+ int ret;
+
+ ret = kstrtobool(buf, &val);
+ if (ret)
+ return ret;
+
+ tty_port_set_nordy(port, val);
+
+ return count;
+}
+
static DEVICE_ATTR_RO(uartclk);
static DEVICE_ATTR_RO(type);
static DEVICE_ATTR_RO(line);
@@ -2884,6 +2908,7 @@ 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,
@@ -2900,6 +2925,7 @@ 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
};

--
2.9.0