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: Jason Wessel <jason.wessel@windriver.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
diff --git a/include/linux/usb/serial.h b/include/linux/usb/serial.h
index 8cdfed7..e2938fd 100644
--- a/include/linux/usb/serial.h
+++ b/include/linux/usb/serial.h
@@ -91,6 +91,9 @@
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 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);