USB: serial: cp210x: fix modem-control handling

The vendor request used to set the flow-control settings also sets the
state of the modem-control lines.

Add state variables to keep track of the modem-control lines to avoid
always asserting the lines whenever the flow-control settings are
updated.

This specifically also avoids asserting DTR/RTS when opening a port with
the line speed set to B0.

Signed-off-by: Johan Hovold <johan@kernel.org>

diff --git a/drivers/usb/serial/cp210x.c b/drivers/usb/serial/cp210x.c
index 7e4a09b..9378b4b 100644 (file)
--- a/drivers/usb/serial/cp210x.c
+++ b/drivers/usb/serial/cp210x.c
@@ -269,6 +269,8 @@ struct cp210x_port_private {
 
        struct mutex            mutex;
        bool                    crtscts;
+       bool                    dtr;
+       bool                    rts;
 };
 
 static struct usb_serial_driver cp210x_device = {
@@ -1162,7 +1164,10 @@ static void cp210x_set_flow_control(struct tty_struct *tty,
        ctl_hs &= ~CP210X_SERIAL_DCD_HANDSHAKE;
        ctl_hs &= ~CP210X_SERIAL_DSR_SENSITIVITY;
        ctl_hs &= ~CP210X_SERIAL_DTR_MASK;
-       ctl_hs |= CP210X_SERIAL_DTR_SHIFT(CP210X_SERIAL_DTR_ACTIVE);
+       if (port_priv->dtr)
+               ctl_hs |= CP210X_SERIAL_DTR_SHIFT(CP210X_SERIAL_DTR_ACTIVE);
+       else
+               ctl_hs |= CP210X_SERIAL_DTR_SHIFT(CP210X_SERIAL_DTR_INACTIVE);
 
        if (C_CRTSCTS(tty)) {
                ctl_hs |= CP210X_SERIAL_CTS_HANDSHAKE;
@@ -1172,7 +1177,10 @@ static void cp210x_set_flow_control(struct tty_struct *tty,
        } else {
                ctl_hs &= ~CP210X_SERIAL_CTS_HANDSHAKE;
                flow_repl &= ~CP210X_SERIAL_RTS_MASK;
-               flow_repl |= CP210X_SERIAL_RTS_SHIFT(CP210X_SERIAL_RTS_ACTIVE);
+               if (port_priv->rts)
+                       flow_repl |= CP210X_SERIAL_RTS_SHIFT(CP210X_SERIAL_RTS_ACTIVE);
+               else
+                       flow_repl |= CP210X_SERIAL_RTS_SHIFT(CP210X_SERIAL_RTS_INACTIVE);
                port_priv->crtscts = false;
        }
 
@@ -1287,25 +1295,29 @@ static int cp210x_tiocmset_port(struct usb_serial_port *port,
        u16 control = 0;
        int ret;
 
+       mutex_lock(&port_priv->mutex);
+
        if (set & TIOCM_RTS) {
+               port_priv->rts = true;
                control |= CONTROL_RTS;
                control |= CONTROL_WRITE_RTS;
        }
        if (set & TIOCM_DTR) {
+               port_priv->dtr = true;
                control |= CONTROL_DTR;
                control |= CONTROL_WRITE_DTR;
        }
        if (clear & TIOCM_RTS) {
+               port_priv->rts = false;
                control &= ~CONTROL_RTS;
                control |= CONTROL_WRITE_RTS;
        }
        if (clear & TIOCM_DTR) {
+               port_priv->dtr = false;
                control &= ~CONTROL_DTR;
                control |= CONTROL_WRITE_DTR;
        }
 
-       mutex_lock(&port_priv->mutex);
-
        /*
         * SET_MHS cannot be used to control RTS when auto-RTS is enabled.
         * Note that RTS is still deasserted when disabling the UART on close.