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, 34 insertions, 13 deletions

diff --git a/drivers/usb/serial/generic.c b/drivers/usb/serial/generic.c
index ad4823bbfa19..1a134f9c64f3 100644
--- a/drivers/usb/serial/generic.c
+++ b/drivers/usb/serial/generic.c
@@ -167,12 +167,35 @@ void usb_serial_generic_close(struct usb_serial_port *port)
 }
 EXPORT_SYMBOL_GPL(usb_serial_generic_close);
 
+int usb_serial_generic_prepare_write_buffer(struct usb_serial_port *port,
+                void **dest, size_t size, const void *src, size_t count)
+{
+        if (!*dest) {
+                size = count;
+                *dest = kmalloc(count, GFP_ATOMIC);
+                if (!*dest) {
+                        dev_err(&port->dev, "%s - could not allocate buffer\n",
+                                        __func__);
+                        return -ENOMEM;
+                }
+        }
+        if (src) {
+                count = size;
+                memcpy(*dest, src, size);
+        } else {
+                count = kfifo_out_locked(&port->write_fifo, *dest, size,
+                                                                &port->lock);
+        }
+        return count;
+}
+EXPORT_SYMBOL_GPL(usb_serial_generic_prepare_write_buffer);
+
 static int usb_serial_multi_urb_write(struct tty_struct *tty,
         struct usb_serial_port *port, const unsigned char *buf, int count)
 {
         unsigned long flags;
         struct urb *urb;
-        unsigned char *buffer;
+        void *buffer;
         int status;
 
         spin_lock_irqsave(&port->lock, flags);
@@ -191,16 +214,14 @@ static int usb_serial_multi_urb_write(struct tty_struct *tty,
                 goto err_urb;
         }
 
+        buffer = NULL;
         count = min_t(int, count, PAGE_SIZE);
-        buffer = kmalloc(count, GFP_ATOMIC);
-        if (!buffer) {
-                dev_err(&port->dev, "%s - could not allocate buffer\n",
-                                __func__);
-                status = -ENOMEM;
+        count = port->serial->type->prepare_write_buffer(port, &buffer, 0,
+                                                                buf, count);
+        if (count < 0) {
+                status = count;
                 goto err_buf;
         }
-
-        memcpy(buffer, buf, count);
         usb_serial_debug_data(debug, &port->dev, __func__, count, buffer);
         usb_fill_bulk_urb(urb, port->serial->dev,
                         usb_sndbulkpipe(port->serial->dev,
@@ -242,7 +263,6 @@ err_urb:
  */
 static int usb_serial_generic_write_start(struct usb_serial_port *port)
 {
-        unsigned char *data;
         int result;
         int count;
         unsigned long flags;
@@ -255,10 +275,11 @@ static int usb_serial_generic_write_start(struct usb_serial_port *port)
         port->write_urb_busy = 1;
         spin_unlock_irqrestore(&port->lock, flags);
 
-        data = port->write_urb->transfer_buffer;
-        count = kfifo_out_locked(&port->write_fifo, data, port->bulk_out_size, &port->lock);
-        usb_serial_debug_data(debug, &port->dev, __func__, count, data);
-
+        count = port->serial->type->prepare_write_buffer(port,
+                                        &port->write_urb->transfer_buffer,
+                                        port->bulk_out_size, NULL, 0);
+        usb_serial_debug_data(debug, &port->dev, __func__,
+                                count, port->write_urb->transfer_buffer);
         port->write_urb->transfer_buffer_length = count;
 
         /* send the data out the bulk port */