[PATCH] USB: ftdi_sio: Update RTS and DTR simultaneously

ftdi_sio: Update RTS and DTR simultaneously, using a single control URB
instead of separate control URBs for RTS and DTR.  Reinhard Bergmann
observed time differences of up to 680 ms with his application on a
2.4.22 kernel when RTS and DTR were updated using separate control
URBs, which is unacceptable.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 43 insertions, 95 deletions

diff --git a/drivers/usb/serial/ftdi_sio.c b/drivers/usb/serial/ftdi_sio.c
index cfb77ceced58..d1d2aeebd20a 100644
--- a/drivers/usb/serial/ftdi_sio.c
+++ b/drivers/usb/serial/ftdi_sio.c
@@ -596,62 +596,59 @@ static __u32 ftdi_232bm_baud_to_divisor(int baud)
          return(ftdi_232bm_baud_base_to_divisor(baud, 48000000));
 }
 
-static int set_rts(struct usb_serial_port *port, int high_or_low)
+#define set_mctrl(port, set)            update_mctrl((port), (set), 0)
+#define clear_mctrl(port, clear)        update_mctrl((port), 0, (clear))
+
+static int update_mctrl(struct usb_serial_port *port, unsigned int set, unsigned int clear)
 {
         struct ftdi_private *priv = usb_get_serial_port_data(port);
         char *buf;
-        unsigned ftdi_high_or_low;
+        unsigned urb_value;
         int rv;
-        
-        buf = kmalloc(1, GFP_NOIO);
-        if (!buf)
-                return -ENOMEM;
-        
-        if (high_or_low) {
-                ftdi_high_or_low = FTDI_SIO_SET_RTS_HIGH;
-                priv->last_dtr_rts |= TIOCM_RTS;
-        } else {
-                ftdi_high_or_low = FTDI_SIO_SET_RTS_LOW;
-                priv->last_dtr_rts &= ~TIOCM_RTS;
-        }
-        rv = usb_control_msg(port->serial->dev,
-                               usb_sndctrlpipe(port->serial->dev, 0),
-                               FTDI_SIO_SET_MODEM_CTRL_REQUEST, 
-                               FTDI_SIO_SET_MODEM_CTRL_REQUEST_TYPE,
-                               ftdi_high_or_low, priv->interface, 
-                               buf, 0, WDR_TIMEOUT);
-
-        kfree(buf);
-        return rv;
-}
 
+        if (((set | clear) & (TIOCM_DTR | TIOCM_RTS)) == 0) {
+                dbg("%s - DTR|RTS not being set|cleared", __FUNCTION__);
+                return 0;       /* no change */
+        }
 
-static int set_dtr(struct usb_serial_port *port, int high_or_low)
-{
-        struct ftdi_private *priv = usb_get_serial_port_data(port);
-        char *buf;
-        unsigned ftdi_high_or_low;
-        int rv;
-        
         buf = kmalloc(1, GFP_NOIO);
-        if (!buf)
+        if (!buf) {
                 return -ENOMEM;
-
-        if (high_or_low) {
-                ftdi_high_or_low = FTDI_SIO_SET_DTR_HIGH;
-                priv->last_dtr_rts |= TIOCM_DTR;
-        } else {
-                ftdi_high_or_low = FTDI_SIO_SET_DTR_LOW;
-                priv->last_dtr_rts &= ~TIOCM_DTR;
         }
+
+        clear &= ~set;  /* 'set' takes precedence over 'clear' */
+        urb_value = 0;
+        if (clear & TIOCM_DTR)
+                urb_value |= FTDI_SIO_SET_DTR_LOW;
+        if (clear & TIOCM_RTS)
+                urb_value |= FTDI_SIO_SET_RTS_LOW;
+        if (set & TIOCM_DTR)
+                urb_value |= FTDI_SIO_SET_DTR_HIGH;
+        if (set & TIOCM_RTS)
+                urb_value |= FTDI_SIO_SET_RTS_HIGH;
         rv = usb_control_msg(port->serial->dev,
                                usb_sndctrlpipe(port->serial->dev, 0),
                                FTDI_SIO_SET_MODEM_CTRL_REQUEST, 
                                FTDI_SIO_SET_MODEM_CTRL_REQUEST_TYPE,
-                               ftdi_high_or_low, priv->interface, 
+                               urb_value, priv->interface,
                                buf, 0, WDR_TIMEOUT);
 
         kfree(buf);
+        if (rv < 0) {
+                err("%s Error from MODEM_CTRL urb: DTR %s, RTS %s",
+                                __FUNCTION__,
+                                (set & TIOCM_DTR) ? "HIGH" :
+                                (clear & TIOCM_DTR) ? "LOW" : "unchanged",
+                                (set & TIOCM_RTS) ? "HIGH" :
+                                (clear & TIOCM_RTS) ? "LOW" : "unchanged");
+        } else {
+                dbg("%s - DTR %s, RTS %s", __FUNCTION__,
+                                (set & TIOCM_DTR) ? "HIGH" :
+                                (clear & TIOCM_DTR) ? "LOW" : "unchanged",
+                                (set & TIOCM_RTS) ? "HIGH" :
+                                (clear & TIOCM_RTS) ? "LOW" : "unchanged");
+                priv->last_dtr_rts = (priv->last_dtr_rts & ~clear) | set;
+        }
         return rv;
 }
 
@@ -1222,12 +1219,7 @@ static int  ftdi_open (struct usb_serial_port *port, struct file *filp)
         /* FIXME: Flow control might be enabled, so it should be checked -
            we have no control of defaults! */
         /* Turn on RTS and DTR since we are not flow controlling by default */
-        if (set_dtr(port, HIGH) < 0) {
-                err("%s Error from DTR HIGH urb", __FUNCTION__);
-        }
-        if (set_rts(port, HIGH) < 0){
-                err("%s Error from RTS HIGH urb", __FUNCTION__);
-        }
+        set_mctrl(port, TIOCM_DTR | TIOCM_RTS);
 
         /* Not throttled */
         spin_lock_irqsave(&priv->rx_lock, flags);
@@ -1277,14 +1269,8 @@ static void ftdi_close (struct usb_serial_port *port, struct file *filp)
                         err("error from flowcontrol urb");
                 }           
 
-                /* drop DTR */
-                if (set_dtr(port, LOW) < 0){
-                        err("Error from DTR LOW urb");
-                }
-                /* drop RTS */
-                if (set_rts(port, LOW) < 0) {
-                        err("Error from RTS LOW urb");
-                }
+                /* drop RTS and DTR */
+                clear_mctrl(port, TIOCM_DTR | TIOCM_RTS);
         } /* Note change no line if hupcl is off */
 
         /* cancel any scheduled reading */
@@ -1815,25 +1801,14 @@ static void ftdi_set_termios (struct usb_serial_port *port, struct termios *old_
                         err("%s error from disable flowcontrol urb", __FUNCTION__);
                 }           
                 /* Drop RTS and DTR */
-                if (set_dtr(port, LOW) < 0){
-                        err("%s Error from DTR LOW urb", __FUNCTION__);
-                }
-                if (set_rts(port, LOW) < 0){
-                        err("%s Error from RTS LOW urb", __FUNCTION__);
-                }       
-                
+                clear_mctrl(port, TIOCM_DTR | TIOCM_RTS);
         } else {
                 /* set the baudrate determined before */
                 if (change_speed(port)) {
                         err("%s urb failed to set baurdrate", __FUNCTION__);
                 }
                 /* Ensure  RTS and DTR are raised */
-                else if (set_dtr(port, HIGH) < 0){
-                        err("%s Error from DTR HIGH urb", __FUNCTION__);
-                }
-                else if (set_rts(port, HIGH) < 0){
-                        err("%s Error from RTS HIGH urb", __FUNCTION__);
-                }       
+                set_mctrl(port, TIOCM_DTR | TIOCM_RTS);
         }
 
         /* Set flow control */
@@ -1945,35 +1920,8 @@ static int ftdi_tiocmget (struct usb_serial_port *port, struct file *file)
 
 static int ftdi_tiocmset(struct usb_serial_port *port, struct file * file, unsigned int set, unsigned int clear)
 {
-        int ret;
-        
         dbg("%s TIOCMSET", __FUNCTION__);
-        if (set & TIOCM_DTR){
-                if ((ret = set_dtr(port, HIGH)) < 0) {
-                        err("Urb to set DTR failed");
-                        return(ret);
-                }
-        }
-        if (set & TIOCM_RTS) {
-                if ((ret = set_rts(port, HIGH)) < 0){
-                        err("Urb to set RTS failed");
-                        return(ret);
-                }
-        }
-        
-        if (clear & TIOCM_DTR){
-                if ((ret = set_dtr(port, LOW)) < 0){
-                        err("Urb to unset DTR failed");
-                        return(ret);
-                }
-        }       
-        if (clear & TIOCM_RTS) {
-                if ((ret = set_rts(port, LOW)) < 0){
-                        err("Urb to unset RTS failed");
-                        return(ret);
-                }
-        }
-        return(0);
+        return update_mctrl(port, set, clear);
 }