+ /*
+ * In a few places sdio_uart_irq() is called directly instead of
+ * waiting for the actual interrupt to be raised and the SDIO IRQ
+ * thread scheduled in order to reduce latency. However, some
+ * interaction with the tty core may end up calling us back
+ * (serial echo, flow control, etc.) through those same places
+ * causing undesirable effects. Let's stop the recursion here.
+ */
+ if (unlikely(port->in_sdio_uart_irq == current))
+ return;
+