USB: serial: generalise write buffer preparation

Generalise write buffer preparation.

This allows for drivers to manipulate (e.g. add headers) to bulk out
data before it is sent.

This adds a new function pointer to usb_serial_driver:

int (*prepare_write_buffer)(struct usb_serial_port *port,
		void **dest, size_t size, const void *src, size_t count);

The function is generic and can be used with either kfifo-based or
multi-urb writes:

If *dest is NULL the implementation should allocate dest.
If src is NULL the implementation should use the port write fifo.

If not set, a generic implementation is used which simply uses memcpy or
kfifo_out.

Signed-off-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 5 insertions, 0 deletions

diff --git a/include/linux/usb/serial.h b/include/linux/usb/serial.h
index 2a3283761600..a4c99ea390e7 100644
--- a/include/linux/usb/serial.h
+++ b/include/linux/usb/serial.h
@@ -277,6 +277,9 @@ struct usb_serial_driver {
         void (*write_bulk_callback)(struct urb *urb);
         /* Called by the generic read bulk callback */
         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);
 };
 #define to_usb_serial_driver(d) \
         container_of(d, struct usb_serial_driver, driver)
@@ -329,6 +332,8 @@ extern void usb_serial_generic_deregister(void);
 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);
 extern int usb_serial_handle_sysrq_char(struct tty_struct *tty,
                                         struct usb_serial_port *port,
                                         unsigned int ch);