[PATCH] USB: ftdi_sio throttling fix

This patch fixes throttling problems in the ftdi_sio driver for the
2.6 kernel.  The old throttling mechanism (unlinking the read urb)
often failed to work, and even it did work, would lose any data
held in the transfer buffer.  The new mechanism presented here is
based on what the whitehead driver does (defer processing and
resubmitting of the read urb until unthrottled).
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>

drivers/usb/serial/ftdi_sio.c

@@ -17,6 +17,9 @@
  * See http://ftdi-usb-sio.sourceforge.net for upto date testing info
  *	and extra documentation
  *
+ * (27/May/2004) Ian Abbott
+ *      Improved throttling code, mostly stolen from the WhiteHEAT driver.
+ *
  * (26/Mar/2004) Jan Capek
  *      Added PID's for ICD-U20/ICD-U40 - incircuit PIC debuggers from CCS Inc.
  *
@@ -584,6 +587,10 @@ static struct usb_driver ftdi_driver = {
 #define BUFSZ 512
 #define PKTSZ 64
 
+/* rx_flags */
+#define THROTTLED		0x01
+#define ACTUALLY_THROTTLED	0x02
+
 struct ftdi_private {
 	ftdi_chip_type_t chip_type;
 				/* type of the device, either SIO or FT8U232AM */
@@ -598,6 +605,8 @@ struct ftdi_private {
 	unsigned long last_dtr_rts;	/* saved modem control outputs */
         wait_queue_head_t delta_msr_wait; /* Used for TIOCMIWAIT */
  	char prev_status, diff_status;        /* Used for TIOCMIWAIT */
+	__u8 rx_flags;		/* receive state flags (throttling) */
+	spinlock_t rx_lock;	/* spinlock for receive state */
 
 	int force_baud;		/* if non-zero, force the baud rate to this value */
 	int force_rtscts;	/* if non-zero, force RTS-CTS to always be enabled */
@@ -625,6 +634,7 @@ static int  ftdi_write_room		(struct usb_serial_port *port);
 static int  ftdi_chars_in_buffer	(struct usb_serial_port *port);
 static void ftdi_write_bulk_callback	(struct urb *urb, struct pt_regs *regs);
 static void ftdi_read_bulk_callback	(struct urb *urb, struct pt_regs *regs);
+static void ftdi_process_read		(struct usb_serial_port *port);
 static void ftdi_set_termios		(struct usb_serial_port *port, struct termios * old);
 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);
@@ -1110,6 +1120,7 @@ static int ftdi_common_startup (struct usb_serial *serial)
 	}
 	memset(priv, 0, sizeof(*priv));
 
+	spin_lock_init(&priv->rx_lock);
         init_waitqueue_head(&priv->delta_msr_wait);
 	/* This will push the characters through immediately rather
 	   than queue a task to deliver them */
@@ -1273,8 +1284,8 @@ static void ftdi_shutdown (struct usb_serial *serial)
 	 */
 
 	if (priv) {
-		kfree(priv);
 		usb_set_serial_port_data(port, NULL);
+		kfree(priv);
 	}
 } /* ftdi_shutdown */
 
@@ -1284,6 +1295,7 @@ static int  ftdi_open (struct usb_serial_port *port, struct file *filp)
 	struct termios tmp_termios;
 	struct usb_device *dev = port->serial->dev;
 	struct ftdi_private *priv = usb_get_serial_port_data(port);
+	unsigned long flags;
 	
 	int result = 0;
 	char buf[1]; /* Needed for the usb_control_msg I think */
@@ -1317,6 +1329,11 @@ static int  ftdi_open (struct usb_serial_port *port, struct file *filp)
 		err("%s Error from RTS HIGH urb", __FUNCTION__);
 	}
 
+	/* Not throttled */
+	spin_lock_irqsave(&priv->rx_lock, flags);
+	priv->rx_flags &= ~(THROTTLED | ACTUALLY_THROTTLED);
+	spin_unlock_irqrestore(&priv->rx_lock, flags);
+
 	/* Start reading from the device */
 	usb_fill_bulk_urb(port->read_urb, dev,
 		      usb_rcvbulkpipe(dev, port->bulk_in_endpointAddress),
@@ -1370,7 +1387,12 @@ static void ftdi_close (struct usb_serial_port *port, struct file *filp)
 	/* shutdown our bulk read */
 	if (port->read_urb) {
 		if (usb_unlink_urb (port->read_urb) < 0) {
-			err("Error unlinking read urb");
+			/* Generally, this isn't an error.  If the previous
+			   read bulk callback occurred (or is about to occur)
+			   while the port was being closed or was throtted
+			   (and is still throttled), the read urb will not
+			   have been submitted. */
+			dbg("%s - failed to unlink read urb (generally not an error)", __FUNCTION__);
 		}
 	}
 } /* ftdi_close */
@@ -1546,13 +1568,6 @@ static void ftdi_read_bulk_callback (struct urb *urb, struct pt_regs *regs)
 	struct usb_serial_port *port = (struct usb_serial_port *)urb->context;
 	struct tty_struct *tty;
 	struct ftdi_private *priv;
-	char error_flag;
-       	unsigned char *data = urb->transfer_buffer;
-
-	int i;
-	int result;
-	int need_flip;
-	int packet_offset;
 
 	if (urb->number_of_packets > 0) {
 		err("%s transfer_buffer_length %d actual_length %d number of packets %d",__FUNCTION__,
@@ -1560,7 +1575,7 @@ static void ftdi_read_bulk_callback (struct urb *urb, struct pt_regs *regs)
 		err("%s transfer_flags %x ", __FUNCTION__,urb->transfer_flags );
 	}
 
-	dbg("%s", __FUNCTION__);
+	dbg("%s - port %d", __FUNCTION__, port->number);
 
 	if (port->open_count <= 0)
 		return;
@@ -1572,6 +1587,14 @@ static void ftdi_read_bulk_callback (struct urb *urb, struct pt_regs *regs)
 	}
 
 	priv = usb_get_serial_port_data(port);
+	if (!priv) {
+		dbg("%s - bad port private data pointer - exiting", __FUNCTION__);
+		return;
+	}
+
+	if (urb != port->read_urb) {
+		err("%s - Not my urb!", __FUNCTION__);
+	}
 
 	if (urb->status) {
 		/* This will happen at close every time so it is a dbg not an err */
@@ -1579,6 +1602,59 @@ static void ftdi_read_bulk_callback (struct urb *urb, struct pt_regs *regs)
 		return;
 	}
 
+	/* If throttled, delay receive processing until unthrottled. */
+	spin_lock(&priv->rx_lock);
+	if (priv->rx_flags & THROTTLED) {
+		dbg("Deferring read urb processing until unthrottled");
+		priv->rx_flags |= ACTUALLY_THROTTLED;
+		spin_unlock(&priv->rx_lock);
+		return;
+	}
+	spin_unlock(&priv->rx_lock);
+
+	ftdi_process_read(port);
+
+} /* ftdi_read_bulk_callback */
+
+
+static void ftdi_process_read (struct usb_serial_port *port)
+{ /* ftdi_process_read */
+	struct urb *urb;
+	struct tty_struct *tty;
+	struct ftdi_private *priv;
+	char error_flag;
+       	unsigned char *data;
+
+	int i;
+	int result;
+	int need_flip;
+	int packet_offset;
+
+	dbg("%s - port %d", __FUNCTION__, port->number);
+
+	if (port->open_count <= 0)
+		return;
+
+	tty = port->tty;
+	if (!tty) {
+		dbg("%s - bad tty pointer - exiting",__FUNCTION__);
+		return;
+	}
+
+	priv = usb_get_serial_port_data(port);
+	if (!priv) {
+		dbg("%s - bad port private data pointer - exiting", __FUNCTION__);
+		return;
+	}
+
+	urb = port->read_urb;
+	if (!urb) {
+		dbg("%s - bad read_urb pointer - exiting", __FUNCTION__);
+		return;
+	}
+
+	data = urb->transfer_buffer;
+
         /* The first two bytes of every read packet are status */
 	if (urb->actual_length > 2) {
 		usb_serial_debug_data (__FILE__, __FUNCTION__, urb->actual_length, data);
@@ -1683,7 +1759,7 @@ static void ftdi_read_bulk_callback (struct urb *urb, struct pt_regs *regs)
 	}
 
 	return;
-} /* ftdi_read_bulk_callback */
+} /* ftdi_process_read */
 
 
 static void ftdi_break_ctl( struct usb_serial_port *port, int break_state )
@@ -2073,27 +2149,32 @@ static int ftdi_ioctl (struct usb_serial_port *port, struct file * file, unsigne
 
 static void ftdi_throttle (struct usb_serial_port *port)
 {
+	struct ftdi_private *priv = usb_get_serial_port_data(port);
+	unsigned long flags;
+
 	dbg("%s - port %d", __FUNCTION__, port->number);
-	usb_unlink_urb (port->read_urb);
+
+	spin_lock_irqsave(&priv->rx_lock, flags);
+	priv->rx_flags |= THROTTLED;
+	spin_unlock_irqrestore(&priv->rx_lock, flags);
 }
 
 
 static void ftdi_unthrottle (struct usb_serial_port *port)
 {
-	int result;
+	struct ftdi_private *priv = usb_get_serial_port_data(port);
+	int actually_throttled;
+	unsigned long flags;
 
 	dbg("%s - port %d", __FUNCTION__, port->number);
 
-	port->read_urb->dev = port->serial->dev;
-
-	usb_fill_bulk_urb(port->read_urb, port->serial->dev, 
-		      usb_rcvbulkpipe(port->serial->dev, port->bulk_in_endpointAddress),
-		      port->read_urb->transfer_buffer, port->read_urb->transfer_buffer_length,
-		      ftdi_read_bulk_callback, port);
+	spin_lock_irqsave(&priv->rx_lock, flags);
+	actually_throttled = priv->rx_flags & ACTUALLY_THROTTLED;
+	priv->rx_flags &= ~(THROTTLED | ACTUALLY_THROTTLED);
+	spin_unlock_irqrestore(&priv->rx_lock, flags);
 
-	result = usb_submit_urb(port->read_urb, GFP_ATOMIC);
-	if (result)
-		err("%s - failed submitting read urb, error %d", __FUNCTION__, result);
+	if (actually_throttled)
+		ftdi_process_read(port);
 }
 
 static int __init ftdi_init (void)