arm64: dts: imx8mm-venice-gw73xx-0x: add dt overlays for serial modes

The imx8mm-venice-gw73xx-0x som+baseboard combination has a multi-protocol
RS-232/RS-485/RS-422 transceiver to an off-board connector which
can be configured in a number of ways via UART and GPIO configuration.

The default configuration per the imx8mm-venice-gw73xx-0x dts is for
UART2 TX/RX and UART4 TX/RX to be available as RS-232:
 J15.1 UART2 TX out
 J15.2 UART2 RX in
 J15.3 UART4 TX out
 J15.4 UART4 RX in
 J15.5 GND

Add dt overlays to allow additional the modes of operation:

rs232-rts (UART2 RS-232 with RTS/CTS hardware flow control)
 J15.1 TX out
 J15.2 RX in
 J15.3 RTS out
 J15.4 CTS in
 J15.5 GND

rs485 (UART2 RS-485 half duplex)
 J15.1 TXRX-
 J15.2 N/C
 J15.3 TXRX+
 J15.4 N/C
 J15.5 GND

rs422 (UART2 RS-422 full duplex)
 J15.1 TX-
 J15.2 RX+
 J15.3 TX+
 J15.4 RX-
 J15.5 GND
Signed-off-by: Tim Harvey <tharvey@gateworks.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm64/boot/dts/freescale/Makefile

@@ -99,6 +99,14 @@ dtb-$(CONFIG_ARCH_MXC) += imx8qxp-colibri-eval-v3.dtb
 dtb-$(CONFIG_ARCH_MXC) += imx8qxp-mek.dtb
 dtb-$(CONFIG_ARCH_MXC) += imx8ulp-evk.dtb
 
+imx8mm-venice-gw73xx-0x-rs232-rts-dtbs	:= imx8mm-venice-gw73xx-0x.dtb imx8mm-venice-gw73xx-0x-rs232-rts.dtbo
+imx8mm-venice-gw73xx-0x-rs422-dtbs	:= imx8mm-venice-gw73xx-0x.dtb imx8mm-venice-gw73xx-0x-rs422.dtbo
+imx8mm-venice-gw73xx-0x-rs485-dtbs	:= imx8mm-venice-gw73xx-0x.dtb imx8mm-venice-gw73xx-0x-rs485.dtbo
+
+dtb-$(CONFIG_ARCH_MXC) += imx8mm-venice-gw73xx-0x-rs232-rts.dtb
+dtb-$(CONFIG_ARCH_MXC) += imx8mm-venice-gw73xx-0x-rs422.dtb
+dtb-$(CONFIG_ARCH_MXC) += imx8mm-venice-gw73xx-0x-rs485.dtb
+
 dtb-$(CONFIG_ARCH_S32) += s32g274a-evb.dtb
 dtb-$(CONFIG_ARCH_S32) += s32g274a-rdb2.dtb
 dtb-$(CONFIG_ARCH_S32) += s32v234-evb.dtb

arch/arm64/boot/dts/freescale/imx8mm-venice-gw73xx-0x-rs232-rts.dts

+// SPDX-License-Identifier: (GPL-2.0+ OR MIT)
+/*
+ * Copyright 2022 Gateworks Corporation
+ *
+ * GW73xx RS232 with RTS/CTS hardware flow control:
+ *  - GPIO4_0 rs485_en needs to be driven low (in-active)
+ *  - UART4_TX becomes RTS
+ *  - UART4_RX becomes CTS
+ */
+
+#include <dt-bindings/gpio/gpio.h>
+
+#include "imx8mm-pinfunc.h"
+
+/dts-v1/;
+/plugin/;
+
+&{/} {
+	compatible = "gw,imx8mm-gw73xx-0x";
+};
+
+&gpio4 {
+	rs485_en {
+		gpio-hog;
+		gpios = <0 GPIO_ACTIVE_HIGH>;
+		output-low;
+		line-name = "rs485_en";
+	};
+};
+
+&uart2 {
+	pinctrl-names = "default";
+	pinctrl-0 = <&pinctrl_uart2>;
+	rts-gpios = <&gpio5 29 GPIO_ACTIVE_LOW>;
+	cts-gpios = <&gpio5 28 GPIO_ACTIVE_LOW>;
+	uart-has-rtscts;
+	status = "okay";
+};
+
+&uart4 {
+	status = "disabled";
+};
+
+&iomuxc {
+	pinctrl_uart2: uart2grp {
+		fsl,pins = <
+			MX8MM_IOMUXC_UART2_RXD_UART2_DCE_RX     0x140
+			MX8MM_IOMUXC_UART2_TXD_UART2_DCE_TX     0x140
+			MX8MM_IOMUXC_UART4_TXD_GPIO5_IO29	0x140
+			MX8MM_IOMUXC_UART4_RXD_GPIO5_IO28	0x140
+		>;
+	};
+};

arch/arm64/boot/dts/freescale/imx8mm-venice-gw73xx-0x-rs422.dts

+// SPDX-License-Identifier: (GPL-2.0+ OR MIT)
+/*
+ * Copyright 2021 Gateworks Corporation
+ *
+ * GW73xx RS422 (RS485 full duplex):
+ *  - GPIO1_0 rs485_term selects on-chip termination
+ *  - GPIO4_0 rs485_en needs to be driven high (active)
+ *  - GPIO4_2 rs485_hd needs to be driven low (in-active)
+ *  - UART4_TX is DE for RS485 transmitter
+ *  - RS485_EN needs to be pulled high
+ *  - RS485_HALF needs to be low
+ */
+
+#include <dt-bindings/gpio/gpio.h>
+
+#include "imx8mm-pinfunc.h"
+
+/dts-v1/;
+/plugin/;
+
+&{/} {
+	compatible = "gw,imx8mm-gw73xx-0x";
+};
+
+&gpio4 {
+	rs485_en {
+		gpio-hog;
+		gpios = <0 GPIO_ACTIVE_HIGH>;
+		output-high;
+		line-name = "rs485_en";
+	};
+
+	rs485_hd {
+		gpio-hog;
+		gpios = <2 GPIO_ACTIVE_HIGH>;
+		output-low;
+		line-name = "rs485_hd";
+	};
+};
+
+&uart2 {
+	pinctrl-names = "default";
+	pinctrl-0 = <&pinctrl_uart2>;
+	rts-gpios = <&gpio5 29 GPIO_ACTIVE_HIGH>;
+	linux,rs485-enabled-at-boot-time;
+	status = "okay";
+};
+
+&uart4 {
+	status = "disabled";
+};
+
+&iomuxc {
+	pinctrl_uart2: uart2grp {
+		fsl,pins = <
+			MX8MM_IOMUXC_UART2_RXD_UART2_DCE_RX     0x140
+			MX8MM_IOMUXC_UART2_TXD_UART2_DCE_TX     0x140
+			MX8MM_IOMUXC_UART4_TXD_GPIO5_IO29	0x140
+		>;
+	};
+};

arch/arm64/boot/dts/freescale/imx8mm-venice-gw73xx-0x-rs485.dts

+// SPDX-License-Identifier: (GPL-2.0+ OR MIT)
+/*
+ * Copyright 2021 Gateworks Corporation
+ *
+ * GW73xx RS485 HD:
+ *  - GPIO1_0 rs485_term selects on-chip termination
+ *  - GPIO4_0 rs485_en needs to be driven high (active)
+ *  - GPIO4_2 rs485_hd needs to be driven high (active)
+ *  - UART4_TX is DE for RS485 transmitter
+ *  - RS485_EN needs to be pulled high
+ *  - RS485_HALF needs to be pulled high
+ */
+
+#include <dt-bindings/gpio/gpio.h>
+
+#include "imx8mm-pinfunc.h"
+
+/dts-v1/;
+/plugin/;
+
+&{/} {
+	compatible = "gw,imx8mm-gw73xx-0x";
+};
+
+&gpio4 {
+	rs485_en {
+		gpio-hog;
+		gpios = <0 GPIO_ACTIVE_HIGH>;
+		output-high;
+		line-name = "rs485_en";
+	};
+
+	rs485_hd {
+		gpio-hog;
+		gpios = <2 GPIO_ACTIVE_HIGH>;
+		output-high;
+		line-name = "rs485_hd";
+	};
+};
+
+&uart2 {
+	pinctrl-names = "default";
+	pinctrl-0 = <&pinctrl_uart2>;
+	rts-gpios = <&gpio5 29 GPIO_ACTIVE_HIGH>;
+	linux,rs485-enabled-at-boot-time;
+	status = "okay";
+};
+
+&uart4 {
+	status = "disabled";
+};
+
+&iomuxc {
+	pinctrl_uart2: uart2grp {
+		fsl,pins = <
+			MX8MM_IOMUXC_UART2_RXD_UART2_DCE_RX     0x140
+			MX8MM_IOMUXC_UART2_TXD_UART2_DCE_TX     0x140
+			MX8MM_IOMUXC_UART4_TXD_GPIO5_IO29	0x140
+		>;
+	};
+};