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    Subject[PATCH 3/5] USB: serial: add sysfs attribute to suppress ready signalling on open
    Date
    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@kernel.org>
    ---
    drivers/usb/serial/bus.c | 38 ++++++++++++++++++++++++++++++++++++--
    1 file changed, 36 insertions(+), 2 deletions(-)

    diff --git a/drivers/usb/serial/bus.c b/drivers/usb/serial/bus.c
    index eb0195cf37dd..37bbeab6666e 100644
    --- a/drivers/usb/serial/bus.c
    +++ b/drivers/usb/serial/bus.c
    @@ -35,6 +35,40 @@ 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);
    + unsigned int val;
    + int ret;
    +
    + ret = kstrtouint(buf, 0, &val);
    + if (ret)
    + return ret;
    +
    + if (val > 1)
    + return -EINVAL;
    +
    + 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_driver *driver;
    @@ -60,8 +94,8 @@ 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;
    --
    2.26.2
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