serial: imx: Fill in rs485_supported

Add information on supported serial_rs485 features.

In the case where RTS is lacking, RS485 cannot be enabled so provide
zero rs485_supported for that case. Perhaps it would make sense to not
provide rs485_config() at all in that case but such a change would have
userspace visible impact/change in behavior so this patch does not
attempt it.
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20220606100433.13793-17-ilpo.jarvinen@linux.intel.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/imx.c

@@ -2200,6 +2200,14 @@ static enum hrtimer_restart imx_trigger_stop_tx(struct hrtimer *t)
 	return HRTIMER_NORESTART;
 }
 
+static const struct serial_rs485 imx_no_rs485 = {};	/* No RS485 if no RTS */
+static const struct serial_rs485 imx_rs485_supported = {
+	.flags = SER_RS485_ENABLED | SER_RS485_RTS_ON_SEND | SER_RS485_RTS_AFTER_SEND |
+		 SER_RS485_RX_DURING_TX,
+	.delay_rts_before_send = 1,
+	.delay_rts_after_send = 1,
+};
+
 /* Default RX DMA buffer configuration */
 #define RX_DMA_PERIODS		16
 #define RX_DMA_PERIOD_LEN	(PAGE_SIZE / 4)
@@ -2279,6 +2287,11 @@ static int imx_uart_probe(struct platform_device *pdev)
 	sport->port.has_sysrq = IS_ENABLED(CONFIG_SERIAL_IMX_CONSOLE);
 	sport->port.ops = &imx_uart_pops;
 	sport->port.rs485_config = imx_uart_rs485_config;
+	/* RTS is required to control the RS485 transmitter */
+	if (sport->have_rtscts || sport->have_rtsgpio)
+		sport->port.rs485_supported = &imx_rs485_supported;
+	else
+		sport->port.rs485_supported = &imx_no_rs485;
 	sport->port.flags = UPF_BOOT_AUTOCONF;
 	timer_setup(&sport->timer, imx_uart_timeout, 0);