serial: sh-sci: Fix fallback to PIO in sci_dma_rx_complete()

When submitting a DMA request fails in sci_dma_rx_complete(), the driver
tries to fall back to PIO, but that does not work: no more data will be
received, or the kernel will even crash.

Fix this similar as in (but not identical to) sci_submit_rx():
  - On SCIF, PIO cannot take over if any DMA transactions are pending,
    hence they must be terminated first.
  - All active cookies must be invalidated, else rx_timer_fn() may
    trigger a NULL pointer dereference.
  - Restarting the port is not needed, as it is already running, but
    serial port interrupts must be directed back from the DMA engine to
    the CPU.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/sh-sci.c

@@ -1337,8 +1337,9 @@ static void sci_dma_rx_complete(void *arg)
 	dev_warn(port->dev, "Failed submitting Rx DMA descriptor\n");
 	/* Switch to PIO */
 	spin_lock_irqsave(&port->lock, flags);
-	s->chan_rx = NULL;
-	sci_start_rx(port);
+	dmaengine_terminate_async(chan);
+	sci_dma_rx_chan_invalidate(s);
+	sci_dma_rx_reenable_irq(s);
 	spin_unlock_irqrestore(&port->lock, flags);
 }