How to enable UART?

[    3.994109] 3100000.serial: ttyTHS1 at MMIO 0x3100000 (irq = 112, base_baud = 0) is a TEGRA_UART
[    3.994548] 3110000.serial: ttyTHS2 at MMIO 0x3110000 (irq = 206, base_baud = 0) is a TEGRA_UART

There’re 2 UART interfaces enabled.

As a result, UART1 has been enabled.

For UART2, please decompile /boot/dtb/kernel_XXX.dtb and modify the following lines:

		serial@3140000 {
			resets = <0x03 0x68>;
			interrupts = <0x00 0x74 0x04>;
			clocks = <0x03 0x9f>;
			dma-names = "rx\0tx";
			compatible = "nvidia,tegra234-uart\0nvidia,tegra20-uart";
-			status = "disabled";
+			status = "okay";
			reg = <0x00 0x3140000 0x00 0x10000>;
			phandle = <0x241>;
			dmas = <0xee 0x14 0xee 0x14>;
		};
..
	aliases {
		i2c3 = "/bus@0/i2c@3190000";
		nvdla1 = "/bus@0/host1x@13e00000/nvdla1@158c0000";
		i2c1 = "/bus@0/i2c@c240000";
		mmc1 = "/bus@0/mmc@3400000";
		i2c8 = "/bus@0/i2c@31e0000";
		i2c6 = "/bus@0/i2c@31c0000";
		serial1 = "/bus@0/serial@3100000";
+		serial3 = "/bus@0/serial@3140000";
		tegra-camera-rtcpu = "/rtcpu@bc00000";
..

Similar steps to enable UART4(serial@3130000).

If you want to modify them in source and recompile kernel image/dtb.
You can modify them in tegra234-p3737-0000+p3701-xxxx-nv-common.dtsi for AGX Orin.