serial: 8250: Mark txvr_ops as a deprecated interface

We added an interface in 8e9e459 ("8250: Allow client drivers to
control tranceivers") for RS-485 transceiver control, but this never
went upstream and is also not a requirement for a client driver to
implement RS-485 transceiver control.

However, this out-of-tree interface got exposed to the NI-Serial drivers,
and they were using it for their driver for the NI 987x devices, so we
can't (yet) drop it outright.

Mark this interface as deprecated and emit a warning when registering a
client driver that intends to use it.

Upstream-Status: Inappropriate [NI-specific]
Signed-off-by: Brenda Streiff <brenda.streiff@ni.com>
Acked-by: Gratian Crisan <gratian.crisan@ni.com>
Acked-by: Jason Smith <jason.smith@ni.com>

Author: bstreiff

drivers/tty/serial/8250/8250_core.c

@@ -1074,8 +1074,12 @@ int serial8250_register_8250_port(const struct uart_8250_port *up)
 			uart->port.serial_out = up->port.serial_out;
 		if (up->port.handle_irq)
 			uart->port.handle_irq = up->port.handle_irq;
-		if (up->port.txvr_ops)
+		if (up->port.txvr_ops) {
+			dev_warn(uart->port.dev,
+				 "txvr_ops is deprecated and will be removed in a future release\n");
+
 			uart->port.txvr_ops = up->port.txvr_ops;
+		}
 		/*  Possibly override set_termios call */
 		if (up->port.set_termios)
 			uart->port.set_termios = up->port.set_termios;

include/linux/serial_core.h

@@ -567,7 +567,7 @@ struct uart_port {
 	unsigned int		frame_time;		/* frame timing in ns */
 	unsigned int		type;			/* port type */
 	const struct uart_ops	*ops;
-	const struct txvr_ops	*txvr_ops;		/* transceiver ops */
+	const struct txvr_ops	*txvr_ops;		/* transceiver ops (deprecated) */
 	unsigned int		custom_divisor;
 	unsigned int		line;			/* port index */
 	unsigned int		minor;