ramips: add support for ASUS RT-AX53U

Specifications:
- Device: ASUS RT-AX53U
- SoC: MT7621AT
- Flash: 128MB
- RAM: 256MB
- Switch: 1 WAN, 3 LAN (10/100/1000 Mbps)
- WiFi: MT7905 2x2 2.4G + MT7975 2x2 5G
- Ports: USB 3.0
- LEDs: 1x POWER (blue, configurable)
        3x LAN (blue, configurable)
        1x WAN (blue, configurable)
        1x USB (blue, not configurable)
	1x 2.4G (blue, not configurable)
	1x 5G (blue, not configurable)

Flash by U-Boot TFTP method:
- Configure your PC with IP 192.168.1.2
- Set up TFTP server and put the factory.bin image on your PC
- Connect serial port(rate:115200) and turn on AP, then interrupt "U-Boot Boot Menu" by hitting any key
   Select "2. Upgrade firmware"
   Press enter when show "Run firmware after upgrading? (Y/n):"
   Select 0 for TFTP method
   Input U-Boot's IP address: 192.168.1.1
   Input TFTP server's IP address: 192.168.1.2
   Input IP netmask: 255.255.255.0
   Input file name: openwrt-ramips-mt7621-asus_rt-ax53u-squashfs-factory.bin
- Restart AP aftre see the log "Firmware upgrade completed!"

Signed-off-by: Chuncheng Chen <ccchen1984@gmail.com>
(replaced led label, added key-* prefix to buttons, added note about
BBT)
Signed-off-by: Christian Lamparter <chunkeey@gmail.com>

target/linux/ramips/dts/mt7621_asus_rt-ax53u.dts

@@ -0,0 +1,164 @@
+// SPDX-License-Identifier: GPL-2.0-or-later OR MIT
+
+#include "mt7621.dtsi"
+
+#include <dt-bindings/gpio/gpio.h>
+#include <dt-bindings/input/input.h>
+#include <dt-bindings/leds/common.h>
+
+/ {
+	compatible = "asus,rt-ax53u", "mediatek,mt7621-soc";
+	model = "ASUS RT-AX53U";
+
+	aliases {
+		led-boot = &led_power;
+		led-failsafe = &led_power;
+		led-running = &led_power;
+		led-upgrade = &led_power;
+		label-mac-device = &gmac0;
+	};
+
+	chosen {
+		bootargs = "console=ttyS0,115200";
+		bootargs-override = "console=ttyS0,115200";
+	};
+
+	leds {
+		compatible = "gpio-leds";
+
+		led_power: led-0 {
+			color = <LED_COLOR_ID_BLUE>;
+                        function = LED_FUNCTION_POWER;
+			gpios = <&gpio 13 GPIO_ACTIVE_LOW>;
+		};
+	};
+
+	keys {
+		compatible = "gpio-keys";
+
+		key-restart {
+			label = "reset";
+			gpios = <&gpio 16 GPIO_ACTIVE_LOW>;
+			linux,code = <KEY_RESTART>;
+		};
+
+		key-wps {
+			label = "wps";
+			gpios = <&gpio 15 GPIO_ACTIVE_LOW>;
+			linux,code = <KEY_WPS_BUTTON>;
+		};
+	};
+};
+
+&nand {
+	status = "okay";
+
+	partitions {
+		compatible = "fixed-partitions";
+		#address-cells = <1>;
+		#size-cells = <1>;
+
+		partition@0 {
+			label = "u-boot";
+			reg = <0x0 0xe0000>;
+			read-only;
+		};
+
+		partition@e0000 {
+			label = "u-boot-env";
+			reg = <0xe0000 0x100000>;
+			read-only;
+		};
+
+		factory: partition@1e0000 {
+			label = "factory";
+			reg = <0x1e0000 0x100000>;
+			read-only;
+
+			compatible = "nvmem-cells";
+			#address-cells = <1>;
+			#size-cells = <1>;
+
+			macaddr_factory_4: macaddr@4 {
+				reg = <0x4 0x6>;
+			};
+		};
+
+		factory2: partition@2e0000 {
+			label = "factory2";
+			reg = <0x2e0000 0x100000>;
+			read-only;
+		};
+
+		partition@3e0000 {
+			label = "kernel";
+			reg = <0x3e0000 0x400000>;
+		};
+
+		partition@7e0000 {
+			label = "ubi";
+			reg = <0x7e0000 0x2e00000>;
+		};
+
+		partition@35e0000 {
+			label = "firmware2";
+			reg = <0x35e0000 0x3200000>;
+		};
+
+		/* Last 8M possibly store the bad block table */
+	};
+};
+
+&pcie {
+	status = "okay";
+};
+
+&pcie1 {
+	wifi@0,0 {
+		compatible = "mediatek,mt76";
+		reg = <0x0000 0 0 0 0>;
+		mediatek,mtd-eeprom = <&factory 0x0000>;
+	};
+};
+
+&gmac0 {
+	nvmem-cells = <&macaddr_factory_4>;
+	nvmem-cell-names = "mac-address";
+};
+
+&switch0 {
+	ports {
+		port@0 {
+			status = "okay";
+			label = "wan";
+		};
+
+		port@1 {
+			status = "okay";
+			label = "lan1";
+		};
+
+		port@2 {
+			status = "okay";
+			label = "lan2";
+		};
+
+		port@3 {
+			status = "okay";
+			label = "lan3";
+		};
+
+		port@4 {
+			status = "okay";
+			label = "lan4";
+		};
+	};
+};
+
+&state_default {
+	gpio {
+		groups = "i2c", "uart2", "uart3", "jtag", "wdt";
+		function = "gpio";
+	};
+};
+

target/linux/ramips/image/mt7621.mk

@@ -232,6 +232,23 @@ define Device/asus_rt-n56u-b1
 endef
 TARGET_DEVICES += asus_rt-n56u-b1
 
+define Device/asus_rt-ax53u
+  $(Device/dsa-migration)
+  DEVICE_VENDOR := ASUS
+  DEVICE_MODEL := RT-AX53U
+  IMAGE_SIZE := 51200k
+  UBINIZE_OPTS := -E 5
+  BLOCKSIZE := 128k
+  PAGESIZE := 2048
+  KERNEL_SIZE := 4096k
+  IMAGES += factory.bin
+  IMAGE/sysupgrade.bin := sysupgrade-tar | append-metadata
+  IMAGE/factory.bin := append-kernel | pad-to $$(KERNEL_SIZE) | append-ubi | \
+	check-size
+  DEVICE_PACKAGES := kmod-mt7915e kmod-usb3 uboot-envtools
+endef
+TARGET_DEVICES += asus_rt-ax53u
+
 define Device/beeline_smartbox-flash
   $(Device/dsa-migration)
   $(Device/uimage-lzma-loader)

target/linux/ramips/mt7621/base-files/lib/upgrade/platform.sh

@@ -53,6 +53,7 @@ platform_do_upgrade() {
 	ampedwireless,ally-r1900k|\
 	asus,rt-ac65p|\
 	asus,rt-ac85p|\
+	asus,rt-ax53u|\
 	beeline,smartbox-flash|\
 	dlink,dir-1960-a1|\
 	dlink,dir-2640-a1|\