serial: Add common rs485 device tree parsing function

Several drivers have the same device tree parsing code. Create
a common helper function for it.

This patch bases on work done by Sascha Hauer.
Signed-off-by: NUwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/serial_core.c

@@ -3026,5 +3026,41 @@ EXPORT_SYMBOL(uart_resume_port);
 EXPORT_SYMBOL(uart_add_one_port);
 EXPORT_SYMBOL(uart_remove_one_port);
 
+/**
+ * of_get_rs485_mode() - Implement parsing rs485 properties
+ * @np: uart node
+ * @rs485conf: output parameter
+ *
+ * This function implements the device tree binding described in
+ * Documentation/devicetree/bindings/serial/rs485.txt.
+ */
+void of_get_rs485_mode(struct device_node *np, struct serial_rs485 *rs485conf)
+{
+	u32 rs485_delay[2];
+	int ret;
+
+	ret = of_property_read_u32_array(np, "rs485-rts-delay", rs485_delay, 2);
+	if (!ret) {
+		rs485conf->delay_rts_before_send = rs485_delay[0];
+		rs485conf->delay_rts_after_send = rs485_delay[1];
+	} else {
+		rs485conf->delay_rts_before_send = 0;
+		rs485conf->delay_rts_after_send = 0;
+	}
+
+	/*
+	 * clear full-duplex and enabled flags to get to a defined state with
+	 * the two following properties.
+	 */
+	rs485conf->flags &= ~(SER_RS485_RX_DURING_TX | SER_RS485_ENABLED);
+
+	if (of_property_read_bool(np, "rs485-rx-during-tx"))
+		rs485conf->flags |= SER_RS485_RX_DURING_TX;
+
+	if (of_property_read_bool(np, "linux,rs485-enabled-at-boot-time"))
+		rs485conf->flags |= SER_RS485_ENABLED;
+}
+EXPORT_SYMBOL_GPL(of_get_rs485_mode);
+
 MODULE_DESCRIPTION("Serial driver core");
 MODULE_LICENSE("GPL");

include/linux/serial_core.h

@@ -501,4 +501,9 @@ static inline int uart_handle_break(struct uart_port *port)
 					 (cflag) & CRTSCTS || \
 					 !((cflag) & CLOCAL))
 
+/*
+ * Common device tree parsing helpers
+ */
+void of_get_rs485_mode(struct device_node *np, struct serial_rs485 *rs485conf);
+
 #endif /* LINUX_SERIAL_CORE_H */