port to read from
data buffer (in kernel space)
number of bytes of data to transfer
This will read up to len bytes of buffer to the port specified, using the IEEE 1284 transfer mode most recently negotiated to (using parport_negotiate), as long as that mode supports reverse transfers (peripheral to host).
It is the caller's responsibility to ensure that the first len bytes of buffer are available to write to.
This function returns the number of bytes transferred (if zero or positive), or else an error code.