serial: samsung: alloc dma stucture in ourport

When we have "dmas" property in serial node in device-tree, we do
memory alocation for dma structure which will be used in DMA handling
code.

Based on previous work of Sylwester Nawrocki and Lukasz Czerwinski.
Signed-off-by: Robert Baldyga <r.baldyga@samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/samsung.c

@@ -1209,6 +1209,18 @@ static int s3c24xx_serial_init_port(struct s3c24xx_uart_port *ourport,
 	ret = platform_get_irq(platdev, 1);
 	if (ret > 0)
 		ourport->tx_irq = ret;
+	/*
+	 * DMA is currently supported only on DT platforms, if DMA properties
+	 * are specified.
+	 */
+	if (platdev->dev.of_node && of_find_property(platdev->dev.of_node,
+						     "dmas", NULL)) {
+		ourport->dma = devm_kzalloc(port->dev,
+					    sizeof(*ourport->dma),
+					    GFP_KERNEL);
+		if (!ourport->dma)
+			return -ENOMEM;
+	}
 
 	ourport->clk	= clk_get(&platdev->dev, "uart");
 	if (IS_ERR(ourport->clk)) {