USB: serial: cp210x: fix RTS handling

Clearing TIOCM_RTS should always deassert RTS and setting the same bit
should enable auto-RTS if hardware flow control is enabled.

This allows user space to throttle input directly at the source also
when hardware-assisted flow control is enabled and makes dtr_rts()
always deassert both lines during close (when HUPCL is set).

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

diff --git a/drivers/usb/serial/cp210x.c b/drivers/usb/serial/cp210x.c
index 4ba3fb0..f00b736 100644 (file)
--- a/drivers/usb/serial/cp210x.c
+++ b/drivers/usb/serial/cp210x.c
@@ -1166,7 +1166,10 @@ static void cp210x_set_flow_control(struct tty_struct *tty,
        if (C_CRTSCTS(tty)) {
                ctl_hs |= CP210X_SERIAL_CTS_HANDSHAKE;
                flow_repl &= ~CP210X_SERIAL_RTS_MASK;
-               flow_repl |= CP210X_SERIAL_RTS_FLOW_CTL;
+               if (port_priv->rts)
+                       flow_repl |= CP210X_SERIAL_RTS_FLOW_CTL;
+               else
+                       flow_repl |= CP210X_SERIAL_RTS_INACTIVE;
                port_priv->crtscts = true;
        } else {
                ctl_hs &= ~CP210X_SERIAL_CTS_HANDSHAKE;
@@ -1286,6 +1289,8 @@ static int cp210x_tiocmset_port(struct usb_serial_port *port,
                unsigned int set, unsigned int clear)
 {
        struct cp210x_port_private *port_priv = usb_get_serial_port_data(port);
+       struct cp210x_flow_ctl flow_ctl;
+       u32 ctl_hs, flow_repl;
        u16 control = 0;
        int ret;
 
@@ -1313,16 +1318,44 @@ static int cp210x_tiocmset_port(struct usb_serial_port *port,
        }
 
        /*
-        * 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.
+        * Use SET_FLOW to set DTR and enable/disable auto-RTS when hardware
+        * flow control is enabled.
         */
-       if (port_priv->crtscts)
-               control &= ~CONTROL_WRITE_RTS;
+       if (port_priv->crtscts && control & CONTROL_WRITE_RTS) {
+               ret = cp210x_read_reg_block(port, CP210X_GET_FLOW, &flow_ctl,
+                               sizeof(flow_ctl));
+               if (ret)
+                       goto out_unlock;
 
-       dev_dbg(&port->dev, "%s - control = 0x%04x\n", __func__, control);
+               ctl_hs = le32_to_cpu(flow_ctl.ulControlHandshake);
+               flow_repl = le32_to_cpu(flow_ctl.ulFlowReplace);
 
-       ret = cp210x_write_u16_reg(port, CP210X_SET_MHS, control);
+               ctl_hs &= ~CP210X_SERIAL_DTR_MASK;
+               if (port_priv->dtr)
+                       ctl_hs |= CP210X_SERIAL_DTR_ACTIVE;
+               else
+                       ctl_hs |= CP210X_SERIAL_DTR_INACTIVE;
 
+               flow_repl &= ~CP210X_SERIAL_RTS_MASK;
+               if (port_priv->rts)
+                       flow_repl |= CP210X_SERIAL_RTS_FLOW_CTL;
+               else
+                       flow_repl |= CP210X_SERIAL_RTS_INACTIVE;
+
+               flow_ctl.ulControlHandshake = cpu_to_le32(ctl_hs);
+               flow_ctl.ulFlowReplace = cpu_to_le32(flow_repl);
+
+               dev_dbg(&port->dev, "%s - ctrl = 0x%02x, flow = 0x%02x\n",
+                               __func__, ctl_hs, flow_repl);
+
+               ret = cp210x_write_reg_block(port, CP210X_SET_FLOW, &flow_ctl,
+                               sizeof(flow_ctl));
+       } else {
+               dev_dbg(&port->dev, "%s - control = 0x%04x\n", __func__, control);
+
+               ret = cp210x_write_u16_reg(port, CP210X_SET_MHS, control);
+       }
+out_unlock:
        mutex_unlock(&port_priv->mutex);
 
        return ret;