serial: sh-sci: Fix panic when serial console and DMA are enabled

BugLink: http://bugs.launchpad.net/bugs/1698799

commit 3c910176 upstream.

This patch fixes an issue that kernel panic happens when DMA is enabled
and we press enter key while the kernel booting on the serial console.

* An interrupt may occur after sci_request_irq().
* DMA transfer area is initialized by setup_timer() in sci_request_dma()
  and used in interrupt.

If an interrupt occurred between sci_request_irq() and setup_timer() in
sci_request_dma(), DMA transfer area has not been initialized yet.
So, this patch changes the order of sci_request_irq() and
sci_request_dma().

Fixes: 73a19e4c ("serial: sh-sci: Add DMA support.")
Signed-off-by: Takatoshi Akiyama <takatoshi.akiyama.kj@ps.hitachi-solutions.com>
[Shimoda changes the commit log]
Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Cc: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>

drivers/tty/serial/sh-sci.c

@@ -1800,11 +1800,13 @@ static int sci_startup(struct uart_port *port)
 
 	dev_dbg(port->dev, "%s(%d)\n", __func__, port->line);
 
+	sci_request_dma(port);
+
 	ret = sci_request_irq(s);
-	if (unlikely(ret < 0))
+	if (unlikely(ret < 0)) {
+		sci_free_dma(port);
 		return ret;
-
-	sci_request_dma(port);
+	}
 
 	spin_lock_irqsave(&port->lock, flags);
 	sci_start_tx(port);
@@ -1834,8 +1836,8 @@ static void sci_shutdown(struct uart_port *port)
 	}
 #endif
 
-	sci_free_dma(port);
 	sci_free_irq(s);
+	sci_free_dma(port);
 }
 
 static unsigned int sci_scbrr_calc(struct sci_port *s, unsigned int bps,