USB: ftdi_sio: switch to generic write implementation

Switch to the generic, multi-urb, write implementation.

Note that this will also make it fairly easy to use the generic
fifo-based write implementation: simply unset the multi_urb_write flag
and modify prepare_write_buffer (or unset if not using a legacy SIO
device). This may be desirable for instance on an embedded system where
optimal throughput at high baudrates may not be as important as other
factors (e.g. no allocations during runtime and less pressure on host
stack).
Signed-off-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/serial/ftdi_sio.c

 /*
  * USB FTDI SIO driver
  *
+ *	Copyright (C) 2009 - 2010
+ *	    Johan Hovold (jhovold@gmail.com)
  *	Copyright (C) 1999 - 2001
  *	    Greg Kroah-Hartman (greg@kroah.com)
  *          Bill Ryder (bryder@sgi.com)
@@ -49,8 +51,8 @@
 /*
  * Version Information
  */
-#define DRIVER_VERSION "v1.5.0"
-#define DRIVER_AUTHOR "Greg Kroah-Hartman <greg@kroah.com>, Bill Ryder <bryder@sgi.com>, Kuba Ober <kuba@mareimbrium.org>, Andreas Mohr"
+#define DRIVER_VERSION "v1.6.0"
+#define DRIVER_AUTHOR "Greg Kroah-Hartman <greg@kroah.com>, Bill Ryder <bryder@sgi.com>, Kuba Ober <kuba@mareimbrium.org>, Andreas Mohr, Johan Hovold <jhovold@gmail.com>"
 #define DRIVER_DESC "USB FTDI Serial Converters Driver"
 
 static int debug;
@@ -87,9 +89,6 @@ struct ftdi_private {
 				   be enabled */
 
 	unsigned int latency;		/* latency setting in use */
-	spinlock_t tx_lock;	/* spinlock for transmit state */
-	unsigned long tx_outstanding_bytes;
-	unsigned long tx_outstanding_urbs;
 	unsigned short max_packet_size;
 	struct mutex cfg_lock; /* Avoid mess by parallel calls of config ioctl() and change_speed() */
 };
@@ -784,12 +783,9 @@ static int  ftdi_sio_port_remove(struct usb_serial_port *port);
 static int  ftdi_open(struct tty_struct *tty, struct usb_serial_port *port);
 static void ftdi_close(struct usb_serial_port *port);
 static void ftdi_dtr_rts(struct usb_serial_port *port, int on);
-static int  ftdi_write(struct tty_struct *tty, struct usb_serial_port *port,
-			const unsigned char *buf, int count);
-static int  ftdi_write_room(struct tty_struct *tty);
-static int  ftdi_chars_in_buffer(struct tty_struct *tty);
-static void ftdi_write_bulk_callback(struct urb *urb);
 static void ftdi_process_read_urb(struct urb *urb);
+static int ftdi_prepare_write_buffer(struct usb_serial_port *port,
+		void **dest, size_t size, const void *buf, size_t count);
 static void ftdi_set_termios(struct tty_struct *tty,
 			struct usb_serial_port *port, struct ktermios *old);
 static int  ftdi_tiocmget(struct tty_struct *tty, struct file *file);
@@ -816,6 +812,8 @@ static struct usb_serial_driver ftdi_sio_device = {
 	.id_table =		id_table_combined,
 	.num_ports =		1,
 	.bulk_in_size =		512,
+	/* Must modify prepare_write_buffer if multi_urb_write is changed. */
+	.multi_urb_write =	1,
 	.probe =		ftdi_sio_probe,
 	.port_probe =		ftdi_sio_port_probe,
 	.port_remove =		ftdi_sio_port_remove,
@@ -824,11 +822,8 @@ static struct usb_serial_driver ftdi_sio_device = {
 	.dtr_rts =		ftdi_dtr_rts,
 	.throttle =		usb_serial_generic_throttle,
 	.unthrottle =		usb_serial_generic_unthrottle,
-	.write =		ftdi_write,
-	.write_room =		ftdi_write_room,
-	.chars_in_buffer =	ftdi_chars_in_buffer,
 	.process_read_urb =	ftdi_process_read_urb,
-	.write_bulk_callback =	ftdi_write_bulk_callback,
+	.prepare_write_buffer =	ftdi_prepare_write_buffer,
 	.tiocmget =		ftdi_tiocmget,
 	.tiocmset =		ftdi_tiocmset,
 	.ioctl =		ftdi_ioctl,
@@ -844,9 +839,6 @@ static struct usb_serial_driver ftdi_sio_device = {
 #define HIGH 1
 #define LOW 0
 
-/* number of outstanding urbs to prevent userspace DoS from happening */
-#define URB_UPPER_LIMIT	42
-
 /*
  * ***************************************************************************
  * Utility functions
@@ -1536,7 +1528,6 @@ static int ftdi_sio_port_probe(struct usb_serial_port *port)
 	}
 
 	kref_init(&priv->kref);
-	spin_lock_init(&priv->tx_lock);
 	mutex_init(&priv->cfg_lock);
 	init_waitqueue_head(&priv->delta_msr_wait);
 
@@ -1761,31 +1752,15 @@ static void ftdi_close(struct usb_serial_port *port)
  *
  * The new devices do not require this byte
  */
-static int ftdi_write(struct tty_struct *tty, struct usb_serial_port *port,
-			   const unsigned char *buf, int count)
+static int ftdi_prepare_write_buffer(struct usb_serial_port *port,
+		void **dest, size_t size, const void *src, size_t count)
 {
-	struct ftdi_private *priv = usb_get_serial_port_data(port);
-	struct urb *urb;
+	struct ftdi_private *priv;
 	unsigned char *buffer;
 	int data_offset ;       /* will be 1 for the SIO and 0 otherwise */
-	int status;
 	int transfer_size;
-	unsigned long flags;
-
-	dbg("%s port %d, %d bytes", __func__, port->number, count);
 
-	if (count == 0) {
-		dbg("write request of 0 bytes");
-		return 0;
-	}
-	spin_lock_irqsave(&priv->tx_lock, flags);
-	if (priv->tx_outstanding_urbs > URB_UPPER_LIMIT) {
-		spin_unlock_irqrestore(&priv->tx_lock, flags);
-		dbg("%s - write limit hit", __func__);
-		return 0;
-	}
-	priv->tx_outstanding_urbs++;
-	spin_unlock_irqrestore(&priv->tx_lock, flags);
+	priv = usb_get_serial_port_data(port);
 
 	data_offset = priv->write_offset;
 	dbg("data_offset set to %d", data_offset);
@@ -1801,17 +1776,9 @@ static int ftdi_write(struct tty_struct *tty, struct usb_serial_port *port,
 
 	buffer = kmalloc(transfer_size, GFP_ATOMIC);
 	if (!buffer) {
-		dev_err(&port->dev,
-			"%s ran out of kernel memory for urb ...\n", __func__);
-		count = -ENOMEM;
-		goto error_no_buffer;
-	}
-
-	urb = usb_alloc_urb(0, GFP_ATOMIC);
-	if (!urb) {
-		dev_err(&port->dev, "%s - no more free urbs\n", __func__);
-		count = -ENOMEM;
-		goto error_no_urb;
+		dev_err(&port->dev, "%s - could not allocate buffer\n",
+				__func__);
+		return -ENOMEM;
 	}
 
 	/* Copy data */
@@ -1821,7 +1788,7 @@ static int ftdi_write(struct tty_struct *tty, struct usb_serial_port *port,
 		int user_pktsz = priv->max_packet_size - data_offset;
 		int todo = count;
 		unsigned char *first_byte = buffer;
-		const unsigned char *current_position = buf;
+		const unsigned char *current_position = src;
 
 		while (todo > 0) {
 			if (user_pktsz > todo)
@@ -1836,134 +1803,14 @@ static int ftdi_write(struct tty_struct *tty, struct usb_serial_port *port,
 			todo -= user_pktsz;
 		}
 	} else {
-		/* No control byte required. */
-		/* Copy in the data to send */
-		memcpy(buffer, buf, count);
+		memcpy(buffer, src, count);
 	}
 
-	usb_serial_debug_data(debug, &port->dev, __func__,
-						transfer_size, buffer);
-
-	/* fill the buffer and send it */
-	usb_fill_bulk_urb(urb, port->serial->dev,
-			usb_sndbulkpipe(port->serial->dev,
-					port->bulk_out_endpointAddress),
-			buffer, transfer_size,
-			ftdi_write_bulk_callback, port);
-
-	status = usb_submit_urb(urb, GFP_ATOMIC);
-	if (status) {
-		dev_err(&port->dev,
-			"%s - failed submitting write urb, error %d\n",
-			__func__, status);
-		count = status;
-		goto error;
-	} else {
-		spin_lock_irqsave(&priv->tx_lock, flags);
-		priv->tx_outstanding_bytes += count;
-		spin_unlock_irqrestore(&priv->tx_lock, flags);
-	}
+	*dest = buffer;
 
-	/* we are done with this urb, so let the host driver
-	 * really free it when it is finished with it */
-	usb_free_urb(urb);
-
-	dbg("%s write returning: %d", __func__, count);
-	return count;
-error:
-	usb_free_urb(urb);
-error_no_urb:
-	kfree(buffer);
-error_no_buffer:
-	spin_lock_irqsave(&priv->tx_lock, flags);
-	priv->tx_outstanding_urbs--;
-	spin_unlock_irqrestore(&priv->tx_lock, flags);
 	return count;
 }
 
-/* This function may get called when the device is closed */
-static void ftdi_write_bulk_callback(struct urb *urb)
-{
-	unsigned long flags;
-	struct usb_serial_port *port = urb->context;
-	struct ftdi_private *priv;
-	int data_offset;       /* will be 1 for the SIO and 0 otherwise */
-	unsigned long countback;
-	int status = urb->status;
-
-	/* free up the transfer buffer, as usb_free_urb() does not do this */
-	kfree(urb->transfer_buffer);
-
-	dbg("%s - port %d", __func__, port->number);
-
-	priv = usb_get_serial_port_data(port);
-	if (!priv) {
-		dbg("%s - bad port private data pointer - exiting", __func__);
-		return;
-	}
-	/* account for transferred data */
-	countback = urb->transfer_buffer_length;
-	data_offset = priv->write_offset;
-	if (data_offset > 0) {
-		/* Subtract the control bytes */
-		countback -= (data_offset * DIV_ROUND_UP(countback, priv->max_packet_size));
-	}
-	spin_lock_irqsave(&priv->tx_lock, flags);
-	--priv->tx_outstanding_urbs;
-	priv->tx_outstanding_bytes -= countback;
-	spin_unlock_irqrestore(&priv->tx_lock, flags);
-
-	if (status) {
-		dbg("nonzero write bulk status received: %d", status);
-	}
-
-	usb_serial_port_softint(port);
-}
-
-static int ftdi_write_room(struct tty_struct *tty)
-{
-	struct usb_serial_port *port = tty->driver_data;
-	struct ftdi_private *priv = usb_get_serial_port_data(port);
-	int room;
-	unsigned long flags;
-
-	dbg("%s - port %d", __func__, port->number);
-
-	spin_lock_irqsave(&priv->tx_lock, flags);
-	if (priv->tx_outstanding_urbs < URB_UPPER_LIMIT) {
-		/*
-		 * We really can take anything the user throws at us
-		 * but let's pick a nice big number to tell the tty
-		 * layer that we have lots of free space
-		 */
-		room = 2048;
-	} else {
-		room = 0;
-	}
-	spin_unlock_irqrestore(&priv->tx_lock, flags);
-	return room;
-}
-
-static int ftdi_chars_in_buffer(struct tty_struct *tty)
-{
-	struct usb_serial_port *port = tty->driver_data;
-	struct ftdi_private *priv = usb_get_serial_port_data(port);
-	int buffered;
-	unsigned long flags;
-
-	dbg("%s - port %d", __func__, port->number);
-
-	spin_lock_irqsave(&priv->tx_lock, flags);
-	buffered = (int)priv->tx_outstanding_bytes;
-	spin_unlock_irqrestore(&priv->tx_lock, flags);
-	if (buffered < 0) {
-		dev_err(&port->dev, "%s outstanding tx bytes is negative!\n",
-			__func__);
-		buffered = 0;
-	}
-	return buffered;
-}
-
 static int ftdi_process_packet(struct tty_struct *tty,
 		struct usb_serial_port *port, struct ftdi_private *priv,
 		char *packet, int len)