Coreboot RockPro64 support

On the official list of mainboards supported by coreboot there are two boards listed using the RK3399: Google Gru Chromebook (2017) and RockPro64. Both have a status of “unknown”. There is a src/soc/rockchip/rk3399/ directory that was last updated in 2021.

In 2021 Mortiz Fischer from Google added initial support for the RockPro64 (see mainboard/pine64/rockpro64: Add initial ROCKPro64 support and Gerrit 50625). Unfortunately, the implementation of DDR initialization based on U-Boot code was never completed. The Google Gru Chromebook uses DDR3 SDRAM, however the RockPro64 uses DDR4.

Additionally, comparing the Makefile.mk in the Gru and RockPro64 mainboard directories shows a great deal of potentially missing functionality. Perhaps a reasonable way to quickly determine the support for a board is by runnning:

wc -l src/mainboard/*/*/Makefile.mk | sort -hr

Mortiz was able to get soc/rockchip/rk3399/sdram: Add phy_ctrl_reset merged, which fixed an issue with the RockPro64 in sdram_init(), despite the fact that the RockPro64 support for SDRAM initialization was never merged.

Two additional related changes made by Mortiz were abandoned:

• soc/rockchip/rk3399/sdram: Introduce pctl_start
• soc/rockchip/rk3399/sdram: Move pwrup_srefresh_exit to array

Mortiz had four commits on mfischer/wip-rk3399-lpddr4 with the first commit pushed to Gerrit above. The three additional commits are:

• soc/rockchip/rk3399/sdram: Compute stride for 2 channels
• soc/rockchip/rk3399/sdram: Compute stride for 1 channel a
• soc/rockchip/rk3399/sdram: Add rank detection support

Note none of these changes include additional code in src/mainboard/pine64/rockpro64.

• Coreboot on ARM 2016 presentation by Julius Werner on YouTube lists the RK3288 and RK3399 as supported
• Arm Trusted Firmware for coreboot developers 2018 presentation by Julius Werner on YouTube

RockPro64 LPDDR4

The RockPro64 apparently shipped with either 2GB or 4GB. I purchased the 4GB model in October 2018.

• 1600 MHz Micron MT53B LPDDR4 SDRAM

The Google Kukui also uses a LPDDR4 MT53, but specifically the MT53E1G32DXNX.

I can’t find where U-Boot keeps SDRAM initialization code. Perhaps in arch/arm/dts/rk3399-sdram-lpddr4-100.dtsi, but shouldn’t it be board specific?

U-Boot Falcon Mode

As a intermediary step, until the coreboot implementation is complete, it may be possible to use U-Boot SPL in “Falcon Mode” to boot a stage containing a u-root initramfs with partial UEFI support.

Falcone mode requires booting the system with U-Boot and running spl export at the U-Boot prompt to write “parameters” in memory that can then be stored in persistent storage. The parameters presumably include a devicetree and kernel command-line. Then after resetting the system U-Boot SPL can read that data and pass it to the kernel, which is normally the responsibility of U-Boot.

It appears to deafult to reading from NAND, but also support NOR. There are also a falcon_args_file and falcon_image_file that are used in the SPL EXT and FAT filesystem code.

https://elixir.bootlin.com/u-boot/latest/source/doc/develop/falcon.rst