I have been working on getting U-boot upstream up to speed for the Radxa Rock-5B Rockchip RK3588 board.

One of the cool features that I recently published upstream is the ability to boot the board without any kind of non-volatile media (NVM) used.

Rockchip provides a way to boot the second stage using a proprietary protocol called rockusb. When you boot the board into maskrom mode (by holding a button pressed), the bootrom inside the SoC will start the USB into gadget mode and listen to rockusb commands. Then you can basically upload the next stage (in our case the U-boot SPL) via USB directly to the memory and boot it, using rockusb tools like the opensource rockusbrs.

So far, the SPL could only boot from an NVM like eMMC, SD-Card, or SPI flash. What is new with the patches that I sent is the fact that the SPL can now also probe the USB into gadget mode and then try to download the next stage.

For this I selected the DFU (Device Firmware Upgrade) protocol to get the U-boot proper into the memory. SPL will detect that it was booted via rockusb, and then it will wait for DFU commands. Once the board is ready, one can use a tool like dfu-util and just upload the U-boot proper file from the host computer to the board, and SPL will boot it.

Once U-boot proper boots, one can use any network protocol like TFTP to get the kernel, and boot with a file system from e.g. NFS.

In the end, the board boots without the use of any media, which was the goal of this exercise.

This summary is short, with a lot of specific terms, so if you have any questions about DFU, U-boot, SPL, USB, rockusb, or any other thing that may appear new or you want to know more about, feel free to comment or reach out to me!