serial: sh-sci: Fix receive on SCIFA/SCIFB variants with DMA

On SCIFA and SCIFB serial ports with DMA support (i.e. some ports on
R-Car Gen2 and RZ/G1 SoCs), receive DMA operations are submitted before
the DMA channel pointer is initialized.  Hence this fails, and the
driver tries to fall back to PIO.  However, at this early phase in the
initialization sequence, fallback to PIO does not work, leading to a
serial port that cannot receive any data.

Fix this by calling sci_submit_rx() after initialization of the DMA
channel pointer.

Reported-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Fixes: 2c4ee23 ("serial: sh-sci: Postpone DMA release when falling back to PIO")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Tested-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/sh-sci.c

@@ -1614,10 +1614,10 @@ static void sci_request_dma(struct uart_port *port)
 		hrtimer_init(&s->rx_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
 		s->rx_timer.function = rx_timer_fn;
 
+		s->chan_rx_saved = s->chan_rx = chan;
+
 		if (port->type == PORT_SCIFA || port->type == PORT_SCIFB)
 			sci_submit_rx(s);
-
-		s->chan_rx_saved = s->chan_rx = chan;
 	}
 }