serial: core: set missing supported flag for RX during TX GPIO

If the RS485 feature RX-during-TX is supported by means of a GPIO set the
according supported flag. Otherwise setting this feature from userspace may
not be possible, since in uart_sanitize_serial_rs485() the passed RS485
configuration is matched against the supported features and unsupported
settings are thereby removed and thus take no effect.

Cc:  <[email protected]>
Fixes: 163f080 ("serial: core: Add option to output RS485 RX_DURING_TX state via GPIO")
Reviewed-by: Ilpo Järvinen <[email protected]>
Signed-off-by: Lino Sanfilippo <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: linosanfilippo-kunbus

drivers/tty/serial/serial_core.c

@@ -3649,6 +3649,8 @@ int uart_get_rs485_mode(struct uart_port *port)
 	if (IS_ERR(desc))
 		return dev_err_probe(dev, PTR_ERR(desc), "Cannot get rs485-rx-during-tx-gpios\n");
 	port->rs485_rx_during_tx_gpio = desc;
+	if (port->rs485_rx_during_tx_gpio)
+		port->rs485_supported.flags |= SER_RS485_RX_DURING_TX;
 
 	return 0;
 }