USB: serial: add generic support for TIOCSSERIAL

TIOCSSERIAL is a horrid, underspecified, legacy interface which for most
serial devices is only useful for setting the close_delay and
closing_wait parameters.

The closing_wait parameter determines how long to wait for the transfer
buffers to drain during close and the default timeout of 30 seconds may
not be sufficient at low line speeds. In other cases, when for example
flow is stopped, the default timeout may instead be too long.

Add generic support for TIOCSSERIAL and TIOCGSERIAL with handling of the
three common parameters close_delay, closing_wait and line for the
benefit of all USB serial drivers while still allowing drivers to
implement further functionality through the existing callbacks.

This currently includes a few drivers that report their base baud clock
rate even if that is really only of interest when setting custom
divisors through the deprecated ASYNC_SPD_CUST interface; an interface
which only the FTDI driver actually implements.

Some drivers have also been reporting back a fake UART type, something
which should no longer be needed and will be dropped by a follow-on
patch.

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Johan Hovold <johan@kernel.org>

1 files changed, 48 insertions, 5 deletions

diff --git a/drivers/usb/serial/usb-serial.c b/drivers/usb/serial/usb-serial.c
index f53a830f4094..255f562ef1a0 100644
--- a/drivers/usb/serial/usb-serial.c
+++ b/drivers/usb/serial/usb-serial.c
@@ -437,19 +437,62 @@ static void serial_unthrottle(struct tty_struct *tty)
 static int serial_get_serial(struct tty_struct *tty, struct serial_struct *ss)
 {
 	struct usb_serial_port *port = tty->driver_data;
+	struct tty_port *tport = &port->port;
+	unsigned int close_delay, closing_wait;
+
+	mutex_lock(&tport->mutex);
+
+	close_delay = jiffies_to_msecs(tport->close_delay) / 10;
+	closing_wait = tport->closing_wait;
+	if (closing_wait != ASYNC_CLOSING_WAIT_NONE)
+		closing_wait = jiffies_to_msecs(closing_wait) / 10;
+
+	ss->line = port->minor;
+	ss->close_delay = close_delay;
+	ss->closing_wait = closing_wait;
 
 	if (port->serial->type->get_serial)
-		return port->serial->type->get_serial(tty, ss);
-	return -ENOTTY;
+		port->serial->type->get_serial(tty, ss);
+
+	mutex_unlock(&tport->mutex);
+
+	return 0;
 }
 
 static int serial_set_serial(struct tty_struct *tty, struct serial_struct *ss)
 {
 	struct usb_serial_port *port = tty->driver_data;
+	struct tty_port *tport = &port->port;
+	unsigned int close_delay, closing_wait;
+	int ret = 0;
+
+	close_delay = msecs_to_jiffies(ss->close_delay * 10);
+	closing_wait = ss->closing_wait;
+	if (closing_wait != ASYNC_CLOSING_WAIT_NONE)
+		closing_wait = msecs_to_jiffies(closing_wait * 10);
+
+	mutex_lock(&tport->mutex);
+
+	if (!capable(CAP_SYS_ADMIN)) {
+		if (close_delay != tport->close_delay ||
+				closing_wait != tport->closing_wait) {
+			ret = -EPERM;
+			goto out_unlock;
+		}
+	}
 
-	if (port->serial->type->set_serial)
-		return port->serial->type->set_serial(tty, ss);
-	return -ENOTTY;
+	if (port->serial->type->set_serial) {
+		ret = port->serial->type->set_serial(tty, ss);
+		if (ret)
+			goto out_unlock;
+	}
+
+	tport->close_delay = close_delay;
+	tport->closing_wait = closing_wait;
+out_unlock:
+	mutex_unlock(&tport->mutex);
+
+	return ret;
 }
 
 static int serial_ioctl(struct tty_struct *tty,