When using software-level RTS/CTS flow control (or Xon/Xoff), we could leak at most the UART FIFO size of bytes after getting the flow control signal. This is because the bytes might be loaded in the FIFO when the flow control signal comes through and the UART will send them out the wire. Consider a case where I have a UART with a 128 byte FIFO. The TTY_THRESHOLD_THROTTLE is set at 128 bytes in n_tty.c. So, isn't it possible that potentially we lose bytes when moving data to the TTY line discipline buffer? If the line discipline buffer is almost full (say the receiving room is 120 bytes), it calls throttle and even if the other end gets the throttle in time, it could potentially send 128 bytes (but there is only 120 bytes of space in the buffer). So when we are flushing to ldisc, we will transfer only the receive_room amount of data and discard the rest? Is there any way of avoiding this? I know there is no way of knowing what the FIFO size of the other side might be! I was wondering if this happens, could we potentially flag a buffer overflow error? We know how many bytes are coming in from the UART and when we are trying to flush to ldisc, if the count is more than the throttle level, can we return an error? Thanks, Karthik -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
