sixtyfourmb.dts

/dts-v1/;

/ {
	#address-cells = <0x01>;
	#size-cells = <0x01>;
	compatible = "riscv-minimal-nommu";
	model = "riscv-minimal-nommu,qemu";
        interrupt-parent = <&intc>;

	chosen {
		bootargs = "earlycon=uart8250,mmio,0x10000000,1000000 console=ttyS0";
	};

	memory@80000000 {
		device_type = "memory";
		reg = <0x80000000 0x3ffc000>;
	};

	cpus {
		#address-cells = <0x01>;
		#size-cells = <0x00>;
		timebase-frequency = <0xf4240>;

		cpu@0 {
			phandle = <0x01>;
			device_type = "cpu";
			reg = <0x00>;
			status = "okay";
			compatible = "riscv";
			riscv,isa = "rv32ima";
			mmu-type = "riscv,none";

			intc: interrupt-controller {
				#interrupt-cells = <0x01>;
				interrupt-controller;
				compatible = "riscv,cpu-intc";
				phandle = <0x02>;
			};
		};

		cpu-map {

			cluster0 {

				core0 {
					cpu = <0x01>;
				};
			};
		};
	};

	soc {
		#address-cells = <0x01>;
		#size-cells = <0x01>;
		compatible = "simple-bus";
		ranges;

		uart@10000000 {
			clock-frequency = <0x1000000>;
			reg = <0x10000000 0x100>;
			compatible = "ns16850";
		};

		poweroff {
			value = <0x5555>;
			offset = <0x00>;
			regmap = <0x04>;
			compatible = "syscon-poweroff";
		};

		reboot {
			value = <0x7777>;
			offset = <0x00>;
			regmap = <0x04>;
			compatible = "syscon-reboot";
		};

		syscon@11100000 {
			phandle = <0x04>;
			reg = <0x11100000 0x1000>;
			compatible = "syscon";
		};

		clint@11000000 {
			interrupts = <0x03 0x07>;
			reg = <0x11000000 0x10000>;
			compatible = "sifive,clint0", "riscv,clint0";
		};
                virtio_input {
                  compatible = "virtio,mmio";
                  status = "disabled";
                  interrupts = <8>;
                };
	};
};

vm.c

static const uint32_t virtio_base = 0x10010000;
                        if (true) {
                          int soc = fdt_path_offset(v_fdt, "/soc");
                          int virtio = fdt_path_offset(v_fdt, "/soc/virtio_input");
                          fdt_appendprop_addrrange(v_fdt, soc, virtio, "reg", virtio_base, 0x100);
                          fdt_setprop_string(v_fdt, virtio, "status", "okay");
                        }