[PATCH 1/2] serial: Keep rs485 settings for devices without firmware node

[Gerhard Engleder <gerhard@engleder-embedded.com>]

From: Gerhard Engleder <eg@keba.com>

Commit fe7f0fa43cef ("serial: 8250: Support rs485 devicetree properties")
retrieves rs485 properties for 8250 drivers. These properties are read
from the firmware node of the device. If the firmware node does not
exist, then the rs485 flags are still reset. Thus, 8250 driver cannot
set rs485 flags to enable a defined rs485 mode during driver loading.
This is no problem so far, as no 8250 driver sets the rs485 flags.

If no firmware node exist, then it should be possible for the driver to
set a reasonable default rs485 mode. Therefore, reset rs485 flags only
if a firmware node exists.

Signed-off-by: Gerhard Engleder <eg@keba.com>
Cc: Lukas Wunner <lukas@wunner.de>
---
 drivers/tty/serial/serial_core.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index 4757293ece8c..366101f85048 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -3533,7 +3533,13 @@ int uart_get_rs485_mode(struct uart_port *port)
 	u32 rs485_delay[2];
 	int ret;
 
-	if (!(port->rs485_supported.flags & SER_RS485_ENABLED))
+	/*
+	 * Retrieve properties only if rs485 is supported and if a firmware node
+	 * exist. If no firmware node exist, then don't touch rs485 config and
+	 * keep initial rs485 properties set by driver.
+	 */
+	if (!(port->rs485_supported.flags & SER_RS485_ENABLED) ||
+	    !dev_fwnode(dev))
 		return 0;
 
 	ret = device_property_read_u32_array(dev, "rs485-rts-delay",
-- 
2.39.5