Commit 715b1dc0 authored by Jason Wessel's avatar Jason Wessel Committed by Greg Kroah-Hartman
Browse files

USB: usb_debug, usb_generic_serial: implement multi urb write 



The usb_debug driver, when used as the console, will always fail to
insert the carriage return and new line sequence as well as randomly
drop console output.  This is a result of only having the single
write_urb and that the tty layer will have a lock that prevents the
processing of the back to back urb requests.

The solution is to allow more than one urb to be outstanding and have
a slightly deeper transmit queue.  The idea and some code is borrowed
from the ftdi_sio usb driver.

The generic usb serial driver was modified so as to allow the classic
method of 1 write urb, or a multi write urb scheme with N allowed
outstanding urbs where N is controlled by max_in_flight_urbs.  When
max_in_flight_urbs in a "struct usb_serial_driver" is non zero the
multi write urb scheme will be used.

The size of 4000 was selected for the usb_debug driver so that the
driver lowers possibility of losing the queued console messages during
the kernel startup.

Signed-off-by: default avatarJason Wessel <jason.wessel@windriver.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@suse.de>
parent b0cda8c5

drivers/usb/serial/generic.c

+114 −7
Original line number Diff line number Diff line
@@ -190,6 +190,88 @@ void usb_serial_generic_close(struct usb_serial_port *port) 
	generic_cleanup(port);

}



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;

	unsigned char *buffer;

	int status;

	int towrite;

	int bwrite = 0;



	dbg("%s - port %d", __func__, port->number);



	if (count == 0)

		dbg("%s - write request of 0 bytes", __func__);



	while (count > 0) {

		towrite = (count > port->bulk_out_size) ?

			port->bulk_out_size : count;

		spin_lock_irqsave(&port->lock, flags);

		if (port->urbs_in_flight >

		    port->serial->type->max_in_flight_urbs) {

			spin_unlock_irqrestore(&port->lock, flags);

			dbg("%s - write limit hit\n", __func__);

			return bwrite;

		}

		port->tx_bytes_flight += towrite;

		port->urbs_in_flight++;

		spin_unlock_irqrestore(&port->lock, flags);



		buffer = kmalloc(towrite, GFP_ATOMIC);

		if (!buffer) {

			dev_err(&port->dev,

			"%s ran out of kernel memory for urb ...\n", __func__);

			goto error_no_buffer;

		}



		urb = usb_alloc_urb(0, GFP_ATOMIC);

		if (!urb) {

			dev_err(&port->dev, "%s - no more free urbs\n",

				__func__);

			goto error_no_urb;

		}



		/* Copy data */

		memcpy(buffer, buf + bwrite, towrite);

		usb_serial_debug_data(debug, &port->dev, __func__,

				      towrite, 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, towrite,

			usb_serial_generic_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);

			goto error;

		}



		/* This urb is the responsibility of the host driver now */

		usb_free_urb(urb);

		dbg("%s write: %d", __func__, towrite);

		count -= towrite;

		bwrite += towrite;

	}

	return bwrite;



error:

	usb_free_urb(urb);

error_no_urb:

	kfree(buffer);

error_no_buffer:

	spin_lock_irqsave(&port->lock, flags);

	port->urbs_in_flight--;

	port->tx_bytes_flight -= towrite;

	spin_unlock_irqrestore(&port->lock, flags);

	return bwrite;

}



int usb_serial_generic_write(struct tty_struct *tty,

	struct usb_serial_port *port, const unsigned char *buf, int count)

{
@@ -207,6 +289,11 @@ int usb_serial_generic_write(struct tty_struct *tty, 
	/* only do something if we have a bulk out endpoint */

	if (serial->num_bulk_out) {

		unsigned long flags;



		if (serial->type->max_in_flight_urbs)

			return usb_serial_multi_urb_write(tty, port,

							  buf, count);



		spin_lock_irqsave(&port->lock, flags);

		if (port->write_urb_busy) {

			spin_unlock_irqrestore(&port->lock, flags);
@@ -257,15 +344,18 @@ 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 = 0;



	dbg("%s - port %d", __func__, port->number);



	/* FIXME: Locking */

	if (serial->num_bulk_out) {

		if (!(port->write_urb_busy))

	spin_lock_irqsave(&port->lock, flags);

	if (serial->type->max_in_flight_urbs) {

		if (port->urbs_in_flight < serial->type->max_in_flight_urbs)

			room = port->bulk_out_size;

	} else if (serial->num_bulk_out && !(port->write_urb_busy)) {

		room = port->bulk_out_size;

	}

	spin_unlock_irqrestore(&port->lock, flags);



	dbg("%s - returns %d", __func__, room);

	return room;
@@ -276,11 +366,16 @@ 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;

	int chars = 0;

	unsigned long flags;



	dbg("%s - port %d", __func__, port->number);



	if (serial->type->max_in_flight_urbs) {

		spin_lock_irqsave(&port->lock, flags);

		chars = port->tx_bytes_flight;

		spin_unlock_irqrestore(&port->lock, flags);

	} else if (serial->num_bulk_out) {

		/* FIXME: Locking */

	if (serial->num_bulk_out) {

		if (port->write_urb_busy)

			chars = port->write_urb->transfer_buffer_length;

	}
@@ -363,12 +458,24 @@ EXPORT_SYMBOL_GPL(usb_serial_generic_read_bulk_callback); 


void usb_serial_generic_write_bulk_callback(struct urb *urb)

{

	unsigned long flags;

	struct usb_serial_port *port = urb->context;

	int status = urb->status;



	dbg("%s - port %d", __func__, port->number);



	if (port->serial->type->max_in_flight_urbs) {

		spin_lock_irqsave(&port->lock, flags);

		--port->urbs_in_flight;

		port->tx_bytes_flight -= urb->transfer_buffer_length;

		if (port->urbs_in_flight < 0)

			port->urbs_in_flight = 0;

		spin_unlock_irqrestore(&port->lock, flags);

	} else {

		/* Handle the case for single urb mode */

		port->write_urb_busy = 0;

	}



	if (status) {

		dbg("%s - nonzero write bulk status received: %d",

		    __func__, status);

drivers/usb/serial/usb_debug.c

+2 −0
Original line number Diff line number Diff line
@@ -15,6 +15,7 @@ 
#include <linux/usb.h>

#include <linux/usb/serial.h>



#define URB_DEBUG_MAX_IN_FLIGHT_URBS	4000

#define USB_DEBUG_MAX_PACKET_SIZE	8



static struct usb_device_id id_table [] = {
@@ -46,6 +47,7 @@ static struct usb_serial_driver debug_device = { 
	.id_table =		id_table,

	.num_ports =		1,

	.open =			usb_debug_open,

	.max_in_flight_urbs =	URB_DEBUG_MAX_IN_FLIGHT_URBS,

};



static int __init debug_init(void)

include/linux/usb/serial.h

+4 −0
Original line number Diff line number Diff line
@@ -91,6 +91,9 @@ struct usb_serial_port { 
	int			write_urb_busy;

	__u8			bulk_out_endpointAddress;



	int			tx_bytes_flight;

	int			urbs_in_flight;



	wait_queue_head_t	write_wait;

	struct work_struct	work;

	char			throttled;
@@ -207,6 +210,7 @@ struct usb_serial_driver { 
	struct device_driver	driver;

	struct usb_driver	*usb_driver;

	struct usb_dynids	dynids;

	int			max_in_flight_urbs;



	int (*probe)(struct usb_serial *serial, const struct usb_device_id *id);

	int (*attach)(struct usb_serial *serial);

CRA Git | Maintained and supported by SUSTech CRA and CCSE