+#ifdef CONFIG_SERIAL_SH_SCI_DMA
+ /*
+ * Calculate delay for 1.5 DMA buffers: see
+ * drivers/serial/serial_core.c::uart_update_timeout(). With 10 bits
+ * (CS8), 250Hz, 115200 baud and 64 bytes FIFO, the above function
+ * calculates 1 jiffie for the data plus 5 jiffies for the "slop(e)."
+ * Then below we calculate 3 jiffies (12ms) for 1.5 DMA buffers (3 FIFO
+ * sizes), but it has been found out experimentally, that this is not
+ * enough: the driver too often needlessly runs on a DMA timeout. 20ms
+ * as a minimum seem to work perfectly.
+ */
+ if (s->chan_rx) {
+ s->rx_timeout = (port->timeout - HZ / 50) * s->buf_len_rx * 3 /
+ port->fifosize / 2;
+ dev_dbg(port->dev,
+ "DMA Rx t-out %ums, tty t-out %u jiffies\n",
+ s->rx_timeout * 1000 / HZ, port->timeout);
+ if (s->rx_timeout < msecs_to_jiffies(20))
+ s->rx_timeout = msecs_to_jiffies(20);
+ }
+#endif
+