USB: serial: remove multi-urb write from generic driver

Remove multi-urb write from the generic driver and simplify the
prepare_write_buffer prototype:

	int (*prepare_write_buffer)(struct usb_serial_port *port,
						void *dest, size_t size);

The default implementation simply fills dest with data from port write
fifo but drivers can override it if they need to process the outgoing
data (e.g. add headers).

Turn ftdi_sio into a generic fifo-based driver, which lowers CPU usage
significantly for small writes while retaining maximum throughput.
Signed-off-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/serial/aircable.c

@@ -84,9 +84,10 @@ static const struct usb_device_id id_table[] = {
 MODULE_DEVICE_TABLE(usb, id_table);
 
 static int aircable_prepare_write_buffer(struct usb_serial_port *port,
-		void **dest, size_t size, const void *src, size_t count)
+						void *dest, size_t size)
 {
-	unsigned char *buf = *dest;
+	int count;
+	unsigned char *buf = dest;
 
 	count = kfifo_out_locked(&port->write_fifo, buf + HCI_HEADER_LENGTH,
 					size - HCI_HEADER_LENGTH, &port->lock);
@@ -185,8 +186,6 @@ static struct usb_serial_driver aircable_device = {
 	.id_table = 		id_table,
 	.num_ports =		1,
 	.bulk_out_size =	HCI_COMPLETE_FRAME,
-	/* Must modify prepare_write_buffer if multi_urb_write is changed. */
-	.multi_urb_write =	0,
 	.probe =		aircable_probe,
 	.process_read_urb =	aircable_process_read_urb,
 	.prepare_write_buffer =	aircable_prepare_write_buffer,

drivers/usb/serial/ftdi_sio.c

@@ -781,7 +781,7 @@ static void ftdi_close(struct usb_serial_port *port);
 static void ftdi_dtr_rts(struct usb_serial_port *port, int on);
 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);
+						void *dest, size_t size);
 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);
@@ -808,8 +808,7 @@ 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,
+	.bulk_out_size =	256,
 	.probe =		ftdi_sio_probe,
 	.port_probe =		ftdi_sio_port_probe,
 	.port_remove =		ftdi_sio_port_remove,
@@ -1531,15 +1530,6 @@ static int ftdi_sio_port_probe(struct usb_serial_port *port)
 		quirk->port_probe(priv);
 
 	priv->port = port;
-
-	/* Free port's existing write urb and transfer buffer. */
-	if (port->write_urb) {
-		usb_free_urb(port->write_urb);
-		port->write_urb = NULL;
-	}
-	kfree(port->bulk_out_buffer);
-	port->bulk_out_buffer = NULL;
-
 	usb_set_serial_port_data(port, priv);
 
 	ftdi_determine_type(port);
@@ -1734,8 +1724,7 @@ static void ftdi_close(struct usb_serial_port *port)
 
 	dbg("%s", __func__);
 
-	/* shutdown our bulk read */
-	usb_kill_urb(port->read_urb);
+	usb_serial_generic_close(port);
 	kref_put(&priv->kref, ftdi_sio_priv_release);
 }
 
@@ -1747,40 +1736,34 @@ static void ftdi_close(struct usb_serial_port *port)
  * The new devices do not require this byte
  */
 static int ftdi_prepare_write_buffer(struct usb_serial_port *port,
-		void **dest, size_t size, const void *src, size_t count)
+						void *dest, size_t size)
 {
 	struct ftdi_private *priv;
-	unsigned char *buffer;
-	int len;
+	int count;
+	unsigned long flags;
 
 	priv = usb_get_serial_port_data(port);
 
-	len = count;
-	if (priv->chip_type == SIO && count != 0)
-		len += ((count - 1) / (priv->max_packet_size - 1)) + 1;
-
-	buffer = kmalloc(len, GFP_ATOMIC);
-	if (!buffer) {
-		dev_err(&port->dev, "%s - could not allocate buffer\n",
-				__func__);
-		return -ENOMEM;
-	}
-
 	if (priv->chip_type == SIO) {
-		int i, msg_len;
-
-		for (i = 0; i < len; i += priv->max_packet_size) {
-			msg_len = min_t(int, len - i, priv->max_packet_size) - 1;
-			buffer[i] = (msg_len << 2) + 1;
-			memcpy(&buffer[i + 1], src, msg_len);
-			src += msg_len;
+		unsigned char *buffer = dest;
+		int i, len, c;
+
+		count = 0;
+		spin_lock_irqsave(&port->lock, flags);
+		for (i = 0; i < size - 1; i += priv->max_packet_size) {
+			len = min_t(int, size - i, priv->max_packet_size) - 1;
+			buffer[i] = (len << 2) + 1;
+			c = kfifo_out(&port->write_fifo, &buffer[i + 1], len);
+			if (!c)
+				break;
+			count += c + 1;
 		}
+		spin_unlock_irqrestore(&port->lock, flags);
 	} else {
-		memcpy(buffer, src, count);
+		count = kfifo_out_locked(&port->write_fifo, dest, size,
+								&port->lock);
 	}
 
-	*dest = buffer;
-
 	return count;
 }
 

drivers/usb/serial/generic.c

@@ -26,8 +26,6 @@
 
 static int debug;
 
-#define MAX_TX_URBS		40
-
 #ifdef CONFIG_USB_SERIAL_GENERIC
 
 static int generic_probe(struct usb_interface *interface,
@@ -172,90 +170,9 @@ void usb_serial_generic_close(struct usb_serial_port *port)
 EXPORT_SYMBOL_GPL(usb_serial_generic_close);
 
 int usb_serial_generic_prepare_write_buffer(struct usb_serial_port *port,
-		void **dest, size_t size, const void *src, size_t count)
+						void *dest, size_t size)
 {
-	if (!*dest) {
-		size = count;
-		*dest = kmalloc(count, GFP_ATOMIC);
-		if (!*dest) {
-			dev_err(&port->dev, "%s - could not allocate buffer\n",
-					__func__);
-			return -ENOMEM;
-		}
-	}
-	if (src) {
-		count = size;
-		memcpy(*dest, src, size);
-	} else {
-		count = kfifo_out_locked(&port->write_fifo, *dest, size,
-								&port->lock);
-	}
-	return count;
-}
-EXPORT_SYMBOL_GPL(usb_serial_generic_prepare_write_buffer);
-
-static int usb_serial_multi_urb_write(struct tty_struct *tty,
-	struct usb_serial_port *port, const unsigned char *buf, int count)
-{
-	unsigned long flags;
-	struct urb *urb;
-	void *buffer;
-	int status;
-
-	spin_lock_irqsave(&port->lock, flags);
-	if (port->tx_urbs == MAX_TX_URBS) {
-		spin_unlock_irqrestore(&port->lock, flags);
-		dbg("%s - write limit hit", __func__);
-		return 0;
-	}
-	port->tx_urbs++;
-	spin_unlock_irqrestore(&port->lock, flags);
-
-	urb = usb_alloc_urb(0, GFP_ATOMIC);
-	if (!urb) {
-		dev_err(&port->dev, "%s - no free urbs available\n", __func__);
-		status = -ENOMEM;
-		goto err_urb;
-	}
-
-	buffer = NULL;
-	count = min_t(int, count, PAGE_SIZE);
-	count = port->serial->type->prepare_write_buffer(port, &buffer, 0,
-								buf, count);
-	if (count < 0) {
-		status = count;
-		goto err_buf;
-	}
-	usb_serial_debug_data(debug, &port->dev, __func__, count, buffer);
-	usb_fill_bulk_urb(urb, port->serial->dev,
-			usb_sndbulkpipe(port->serial->dev,
-					port->bulk_out_endpointAddress),
-			buffer, count,
-			port->serial->type->write_bulk_callback, port);
-
-	status = usb_submit_urb(urb, GFP_ATOMIC);
-	if (status) {
-		dev_err(&port->dev, "%s - error submitting urb: %d\n",
-				__func__, status);
-		goto err;
-	}
-	spin_lock_irqsave(&port->lock, flags);
-	port->tx_bytes += urb->transfer_buffer_length;
-	spin_unlock_irqrestore(&port->lock, flags);
-
-	usb_free_urb(urb);
-
-	return count;
-err:
-	kfree(buffer);
-err_buf:
-	usb_free_urb(urb);
-err_urb:
-	spin_lock_irqsave(&port->lock, flags);
-	port->tx_urbs--;
-	spin_unlock_irqrestore(&port->lock, flags);
-
-	return status;
+	return kfifo_out_locked(&port->write_fifo, dest, size, &port->lock);
 }
 
 /**
@@ -286,8 +203,8 @@ static int usb_serial_generic_write_start(struct usb_serial_port *port)
 
 	urb = port->write_urbs[i];
 	count = port->serial->type->prepare_write_buffer(port,
-						&urb->transfer_buffer,
-						port->bulk_out_size, NULL, 0);
+						urb->transfer_buffer,
+						port->bulk_out_size);
 	urb->transfer_buffer_length = count;
 	usb_serial_debug_data(debug, &port->dev, __func__, count,
 						urb->transfer_buffer);
@@ -328,7 +245,6 @@ static int usb_serial_generic_write_start(struct usb_serial_port *port)
 int usb_serial_generic_write(struct tty_struct *tty,
 	struct usb_serial_port *port, const unsigned char *buf, int count)
 {
-	struct usb_serial *serial = port->serial;
 	int result;
 
 	dbg("%s - port %d", __func__, port->number);
@@ -340,23 +256,18 @@ int usb_serial_generic_write(struct tty_struct *tty,
 	if (!count)
 		return 0;
 
-	if (serial->type->multi_urb_write)
-		return usb_serial_multi_urb_write(tty, port, buf, count);
-
 	count = kfifo_in_locked(&port->write_fifo, buf, count, &port->lock);
 	result = usb_serial_generic_write_start(port);
+	if (result)
+		return result;
 
-	if (result >= 0)
-		result = count;
-
-	return result;
+	return count;
 }
 EXPORT_SYMBOL_GPL(usb_serial_generic_write);
 
 int usb_serial_generic_write_room(struct tty_struct *tty)
 {
 	struct usb_serial_port *port = tty->driver_data;
-	struct usb_serial *serial = port->serial;
 	unsigned long flags;
 	int room;
 
@@ -366,10 +277,7 @@ int usb_serial_generic_write_room(struct tty_struct *tty)
 		return 0;
 
 	spin_lock_irqsave(&port->lock, flags);
-	if (serial->type->multi_urb_write)
-		room = (MAX_TX_URBS - port->tx_urbs) * PAGE_SIZE;
-	else
-		room = kfifo_avail(&port->write_fifo);
+	room = kfifo_avail(&port->write_fifo);
 	spin_unlock_irqrestore(&port->lock, flags);
 
 	dbg("%s - returns %d", __func__, room);
@@ -379,7 +287,6 @@ int usb_serial_generic_write_room(struct tty_struct *tty)
 int usb_serial_generic_chars_in_buffer(struct tty_struct *tty)
 {
 	struct usb_serial_port *port = tty->driver_data;
-	struct usb_serial *serial = port->serial;
 	unsigned long flags;
 	int chars;
 
@@ -389,10 +296,7 @@ int usb_serial_generic_chars_in_buffer(struct tty_struct *tty)
 		return 0;
 
 	spin_lock_irqsave(&port->lock, flags);
-	if (serial->type->multi_urb_write)
-		chars = port->tx_bytes;
-	else
-		chars = kfifo_len(&port->write_fifo) + port->tx_bytes;
+	chars = kfifo_len(&port->write_fifo) + port->tx_bytes;
 	spin_unlock_irqrestore(&port->lock, flags);
 
 	dbg("%s - returns %d", __func__, chars);
@@ -479,35 +383,25 @@ void usb_serial_generic_write_bulk_callback(struct urb *urb)
 
 	dbg("%s - port %d", __func__, port->number);
 
-	if (port->serial->type->multi_urb_write) {
-		kfree(urb->transfer_buffer);
+	for (i = 0; i < ARRAY_SIZE(port->write_urbs); ++i)
+		if (port->write_urbs[i] == urb)
+			break;
 
-		spin_lock_irqsave(&port->lock, flags);
-		port->tx_bytes -= urb->transfer_buffer_length;
-		port->tx_urbs--;
-		spin_unlock_irqrestore(&port->lock, flags);
-	} else {
-		for (i = 0; i < ARRAY_SIZE(port->write_urbs); ++i)
-			if (port->write_urbs[i] == urb)
-				break;
+	spin_lock_irqsave(&port->lock, flags);
+	port->tx_bytes -= urb->transfer_buffer_length;
+	set_bit(i, &port->write_urbs_free);
+	spin_unlock_irqrestore(&port->lock, flags);
+
+	if (status) {
+		dbg("%s - non-zero urb status: %d", __func__, status);
 
 		spin_lock_irqsave(&port->lock, flags);
-		port->tx_bytes -= urb->transfer_buffer_length;
-		set_bit(i, &port->write_urbs_free);
+		kfifo_reset_out(&port->write_fifo);
 		spin_unlock_irqrestore(&port->lock, flags);
-
-		if (status) {
-			spin_lock_irqsave(&port->lock, flags);
-			kfifo_reset_out(&port->write_fifo);
-			spin_unlock_irqrestore(&port->lock, flags);
-		} else {
-			usb_serial_generic_write_start(port);
-		}
+	} else {
+		usb_serial_generic_write_start(port);
 	}
 
-	if (status)
-		dbg("%s - non-zero urb status: %d", __func__, status);
-
 	usb_serial_port_softint(port);
 }
 EXPORT_SYMBOL_GPL(usb_serial_generic_write_bulk_callback);

include/linux/usb/serial.h

@@ -67,7 +67,6 @@ enum port_dev_state {
  * @write_urbs: pointers to the bulk out urbs for this port
  * @write_urbs_free: status bitmap the for bulk out urbs
  * @tx_bytes: number of bytes currently in host stack queues
- * @tx_urbs: number of urbs currently in host stack queues
  * @bulk_out_endpointAddress: endpoint address for the bulk out pipe for this
  *	port.
  * @flags: usb serial port flags
@@ -112,7 +111,6 @@ struct usb_serial_port {
 	__u8			bulk_out_endpointAddress;
 
 	int			tx_bytes;
-	int			tx_urbs;
 
 	unsigned long		flags;
 	wait_queue_head_t	write_wait;
@@ -238,8 +236,6 @@ struct usb_serial_driver {
 	struct usb_driver	*usb_driver;
 	struct usb_dynids	dynids;
 
-	unsigned char		multi_urb_write:1;
-
 	size_t			bulk_in_size;
 	size_t			bulk_out_size;
 
@@ -291,7 +287,7 @@ struct usb_serial_driver {
 	void (*process_read_urb)(struct urb *urb);
 	/* Called by the generic write implementation */
 	int (*prepare_write_buffer)(struct usb_serial_port *port,
-		void **dest, size_t size, const void *src, size_t count);
+						void *dest, size_t size);
 };
 #define to_usb_serial_driver(d) \
 	container_of(d, struct usb_serial_driver, driver)
@@ -345,7 +341,7 @@ extern int usb_serial_generic_submit_read_urb(struct usb_serial_port *port,
 						 gfp_t mem_flags);
 extern void usb_serial_generic_process_read_urb(struct urb *urb);
 extern int usb_serial_generic_prepare_write_buffer(struct usb_serial_port *port,
-		void **dest, size_t size, const void *src, size_t count);
+						void *dest, size_t size);
 extern int usb_serial_handle_sysrq_char(struct tty_struct *tty,
 					struct usb_serial_port *port,
 					unsigned int ch);