tty: serial: meson: if no alias specified use an available id

At probe, the uart driver tries to get an id from a device tree alias.
When no alias was specified, the driver would return an error and probing
would fail.

Providing an alias for registering a serial device should not be mandatory.
If the device tree does not specify an alias, provide an id from a reserved
range so that the probing can continue.

Suggested-by: Rob Herring <[e-mail]>
Signed-off-by: Loys Ollivier <[e-mail]>
Reviewed-by: Neil Armstrong <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/tty/serial/meson_uart.c

···
 #define AML_UART_BAUD_USE		BIT(23)
 #define AML_UART_BAUD_XTAL		BIT(24)
 
-#define AML_UART_PORT_NUM		6
+#define AML_UART_PORT_NUM		12
+#define AML_UART_PORT_OFFSET		6
 #define AML_UART_DEV_NAME		"ttyAML"
 
 
···
 	struct resource *res_mem, *res_irq;
 	struct uart_port *port;
 	int ret = 0;
+	int id = -1;
 
 	if (pdev->dev.of_node)
 		pdev->id = of_alias_get_id(pdev->dev.of_node, "serial");
+
+	if (pdev->id < 0) {
+		for (id = AML_UART_PORT_OFFSET; id < AML_UART_PORT_NUM; id++) {
+			if (!meson_ports[id]) {
+				pdev->id = id;
+				break;
+			}
+		}
+	}
 
 	if (pdev->id < 0 || pdev->id >= AML_UART_PORT_NUM)
 		return -EINVAL;