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>

1 files changed, 3 insertions, 4 deletions

diff --git a/drivers/usb/serial/aircable.c b/drivers/usb/serial/aircable.c
index cac5162937b3..8a990a763c21 100644
--- a/drivers/usb/serial/aircable.c
+++ b/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,