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USB: usb_debug, usb_generic_serial: implement multi urb write

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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: Jason Wessel <jason.wessel@windriver.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
This commit is contained in:
Jason Wessel 2009-05-11 15:24:07 -05:00 • committed by Greg Kroah-Hartman
parent b0cda8c5f7
commit 715b1dc01f
3 changed files with 120 additions and 7 deletions
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2
drivers/usb/serial/usb_debug.c
View file

@ -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)