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, 2 insertions, 6 deletions

diff --git a/include/linux/usb/serial.h b/include/linux/usb/serial.h
index 70b6d6b28997..061c997ae0cf 100644
--- a/include/linux/usb/serial.h
+++ b/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);