serial: sh-sci: disable DMA for uart_console

commit 099506cbbc79c0bd52b19cb6b930f256dabc3950 upstream.

As noted in commit 84b40e3b ("serial: 8250: omap: Disable DMA for
console UART"), UART console lines use low-level PIO only access functions
which will conflict with use of the line when DMA is enabled, e.g. when
the console line is also used for systemd messages. So disable DMA
support for UART console lines.
Reported-by: NMichael Rodin <mrodin@de.adit-jv.com>
Link: https://patchwork.kernel.org/patch/10929511/Tested-by: NEugeniu Rosca <erosca@de.adit-jv.com>
Reviewed-by: NSimon Horman <horms+renesas@verge.net.au>
Reviewed-by: NWolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: NGeert Uytterhoeven <geert+renesas@glider.be>
Cc: stable@vger.kernel.org
Signed-off-by: NGeorge G. Davis <george_davis@mentor.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/sh-sci.c

@@ -1542,6 +1542,13 @@ static void sci_request_dma(struct uart_port *port)
 
 	dev_dbg(port->dev, "%s: port %d\n", __func__, port->line);
 
+	/*
+	 * DMA on console may interfere with Kernel log messages which use
+	 * plain putchar(). So, simply don't use it with a console.
+	 */
+	if (uart_console(port))
+		return;
+
 	if (!port->dev->of_node)
 		return;