[PATCH v2 4/6] USB: serial: add sysfs attribute to suppress ready signalling on open

Mychaela N. Falconia
2022-05-31T04:37:13Z

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>
---
drivers/usb/serial/bus.c | 35 +++++++++++++++++++++++++++++++++--
1 file changed, 33 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/serial/bus.c b/drivers/usb/serial/bus.c
index 9e38142acd38..25f8218b2bce 100644
--- a/drivers/usb/serial/bus.c
+++ b/drivers/usb/serial/bus.c
@@ -29,6 +29,37 @@ static int usb_serial_device_match(struct device *dev,
return 0;
}

+static ssize_t nordy_show(struct device *dev, struct device_attribute *attr,
+ char *buf)
+{
+ struct usb_serial_port *port = dev_get_drvdata(dev);
+
+ return sprintf(buf, "%d\n", tty_port_nordy(&port->port));
+}
+
+static ssize_t nordy_store(struct device *dev, struct device_attribute *attr,
+ const char *buf, size_t count)
+{
+ struct usb_serial_port *port = dev_get_drvdata(dev);
+ bool val;
+ int ret;
+
+ ret = kstrtobool(buf, &val);
+ if (ret)
+ return ret;
+
+ tty_port_set_nordy(&port->port, val);
+
+ return count;
+}
+static DEVICE_ATTR_RW(nordy);
+
+static struct attribute *tty_attrs[] = {
+ &dev_attr_nordy.attr,
+ NULL
+};
+ATTRIBUTE_GROUPS(tty);
+
static int usb_serial_device_probe(struct device *dev)
{
struct usb_serial_port *port = to_usb_serial_port(dev);
@@ -50,8 +81,8 @@ static int usb_serial_device_probe(struct device *dev)
}

minor = port->minor;
- tty_dev = tty_port_register_device(&port->port, usb_serial_tty_driver,
- minor, dev);
+ tty_dev = tty_port_register_device_attr(&port->port,
+ usb_serial_tty_driver, minor, dev, port, tty_groups);
if (IS_ERR(tty_dev)) {
retval = PTR_ERR(tty_dev);
goto err_port_remove;
--
2.9.0