rock960c

[Trevor Woerner <twoerner@gmail.com>]

Hi,

I was hoping that one day support would be added for the rockchip rock960c
board (from the 96boards series, https://www.96boards.org/product/rock960c/).
NOTE: this board is different from the rock960 board (aka rock960 a/b) that is
currently supported.

Schematics and datasheets aren't easy to come by. A while back someone
mentioned that the only difference between the rock960 a/b and the rock960c is
that the rock960c uses different SDRAM (LPDDR4 instead of LPDDR3). Searching
around on the Internet it would appear that the rock960c uses the same SDRAM
as the rock-pi-4 devices (maybe?).

The actual SDRAM on the board is H9HCNNN4KUML-HRNMN, but I can't find a
datasheet for it anywhere, not even on Hynix's website.

I tried creating a rock960c device by copying the rock960 things. The one
change I made was that my rk3399-rock960c-u-boot.dtsi file has:

	#include "rk3399-sdram-lpddr4-100.dtsi"

(which is what the rock-pi-4 is using) instead of:

	#include "rk3399-sdram-lpddr3-2GB-1600.dtsi"

(which is what rk3399-rock960-u-boot.dtsi is using). Unfortunately this
doesn't succeed. The TPL is invoked, then there's nothing else on the console:

	U-Boot TPL 2021.04 (Jun 30 2021 - 18:16:57)

I then tried building and using the vendor-supplied u-boot fork for the
rock960c which is found here:

	git://github.com/96rocks/u-boot.git

but it is quite old (U-Boot 2017.09) and pre-dates the TPL/idbloader things.
If I understand things correctly, the vendor branch only builds u-boot and the
spl, I then need to mash in some sort of binary ddr file to the spl to get a
working first-stage bootloader (?). I'm unclear how to take the build output
from the vendor branch and create a working bootloader to load on my sdcard
(the only docs for the rk3399 in that branch are generic and don't refer to
things that come out of the build for the rock960c).

In any case, if anyone has any any tips etc I'd appreciate it :-)

Best regards,
	Trevor