RK3399 - Linux device trees

It isn't clear yet if I can just give a pointer to trash in memory or if U-boot will validate what it finds there.

The device tree idea is a way to allow the linux kernel to contain generic device drivers with details (like base addresses, interrupt numbers, and such) to be supplied by a device tree. The idea was invented when the linux kernel developers found themselves confronted with a myriad of ARM based boards with minor differences in details. Rather than generating a custom kernel for each one, the hope was that one kernel could be generated and a device tree alongside of it could supply details. I'll be honest that I am skeptical. At least I have not found that much in common between the various ARM based boards I am working with. But I am not making the decisions, and this is clearly an entrenched practice at this stage.
Here is an explanation from the horses mouth:

• Linux and the device tree
• Device tree syntax and structure (Zephr)
• The Devicetree Specification
• Device Tree structure (Nvidia)

The Zephyr link above seems to be the best explanation of the syntax. The Linux article explains the big concepts.

The syntax of the source files is one thing. Using the information in the tree from a device driver is something else entirely that I will ignore here. There is a well defined API for doing that and looking up information.

Getting started

First an xyz.dts file for a board is prepared. This is plain ascii. It is also possible (and common) to have abc.dtsi files ("i" for include). Then the dts file ("s" for source) is compiled into a dtb file ("b" for binary).
This is done with the "dtc" tool ("c" for compiler) as follows:

dtc -I dts -O dtb -o myboard.dtb myboard.dts

On my Fedora system, I needed to install dtc:

su ; dnf install dtc
[3/4] Installing libfdt-0:1.7.2-3.fc42
[4/4] Installing dtc-0:1.7.2-3.fc42

Here is a short bit of zynq-zc702.dts

/dts-v1/;
#include "zynq-7000.dtsi"

/ {
    model = "Xilinx ZC702 board";
    compatible = "xlnx,zynq-zc702", "xlnx,zynq-7000";

    aliases {
        ethernet0 = &gem0;
        serial0 = &uart1;
    };
    memory@0 {
        device_type = "memory";
        reg = <0x0 0x40000000>;
    };
	&uart1 {
		status = "okay";
		pinctrl-names = "default";
		pinctrl-0 = <&pinctrl_uart1_default>;
	};
};

A minimal device tree

/* Bogus empty device tree
 */
/dts-v1/;

/ {
    model = "Totally bogus";
};

dtc -I dts -O dtb -o bogus.dtb bogus.dts

dhcp
tftpboot 03000000 bogus.dtb
booti 0x02000000 - 03000000