nds32: Device tree support

This patch adds support for device tree.
Signed-off-by: Vincent Chen <vincentc@andestech.com>
Signed-off-by: Greentime Hu <greentime@andestech.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>

arch/nds32/boot/dts/Makefile

+ifneq '$(CONFIG_NDS32_BUILTIN_DTB)' '""'
+BUILTIN_DTB := $(patsubst "%",%,$(CONFIG_NDS32_BUILTIN_DTB)).dtb.o
+else
+BUILTIN_DTB :=
+endif
+obj-$(CONFIG_OF) += $(BUILTIN_DTB)
+
+clean-files := *.dtb *.dtb.S

arch/nds32/boot/dts/ae3xx.dts

+/dts-v1/;
+/ {
+	compatible = "andestech,ae3xx";
+	#address-cells = <1>;
+	#size-cells = <1>;
+	interrupt-parent = <&intc>;
+
+	chosen {
+		stdout-path = &serial0;
+	};
+
+	memory@0 {
+		device_type = "memory";
+		reg = <0x00000000 0x40000000>;
+	};
+
+	cpus {
+		#address-cells = <1>;
+		#size-cells = <0>;
+		cpu@0 {
+			device_type = "cpu";
+			compatible = "andestech,n13", "andestech,nds32v3";
+			reg = <0>;
+			clock-frequency = <60000000>;
+			next-level-cache = <&L2>;
+		};
+	};
+
+	intc: interrupt-controller {
+		compatible = "andestech,ativic32";
+		#interrupt-cells = <1>;
+		interrupt-controller;
+	};
+
+	clock: clk {
+		#clock-cells = <0>;
+		compatible = "fixed-clock";
+		clock-frequency = <30000000>;
+	};
+
+	apb {
+		compatible = "simple-bus";
+		#address-cells = <1>;
+		#size-cells = <1>;
+		ranges;
+
+		serial0: serial@f0300000 {
+			compatible = "andestech,uart16550", "ns16550a";
+			reg = <0xf0300000 0x1000>;
+			interrupts = <8>;
+			clock-frequency = <14745600>;
+			reg-shift = <2>;
+			reg-offset = <32>;
+			no-loopback-test = <1>;
+		};
+
+		timer0: timer@f0400000 {
+			compatible = "andestech,atcpit100";
+			reg = <0xf0400000 0x1000>;
+			interrupts = <2>;
+			clocks = <&clock>;
+			clock-names = "PCLK";
+		};
+	};
+
+	ahb {
+		compatible = "simple-bus";
+		#address-cells = <1>;
+		#size-cells = <1>;
+		ranges;
+
+		L2: cache-controller@e0500000 {
+			compatible = "andestech,atl2c";
+			reg = <0xe0500000 0x1000>;
+			cache-unified;
+			cache-level = <2>;
+		};
+
+		mac0: ethernet@e0100000 {
+			compatible = "andestech,atmac100";
+			reg = <0xe0100000 0x1000>;
+			interrupts = <18>;
+		};
+	};
+};

arch/nds32/kernel/devtree.c

+// SPDX-License-Identifier: GPL-2.0
+// Copyright (C) 2005-2017 Andes Technology Corporation
+
+#include <linux/bug.h>
+#include <linux/printk.h>
+#include <linux/of_fdt.h>
+
+void __init early_init_devtree(void *params)
+{
+	if (!params || !early_init_dt_scan(params)) {
+		pr_crit("\n"
+			"Error: invalid device tree blob at (virtual address 0x%p)\n"
+			"\nPlease check your bootloader.", params);
+
+		BUG_ON(1);
+	}
+
+	dump_stack_set_arch_desc("%s (DT)", of_flat_dt_get_machine_name());
+}