rockusb: Ability to download u-boot TPL/SPL binary instead of packed image

[obbardc]

Right now the download-boot command accepts images packed by rkbin's boot_merger a la:

$ tools/boot_merger RKBOOT/RK3399MINIALL.ini
$ rockusb download-boot rk3399_loader_v1.27.126.bin

It'd be great to be able to pass in a u-boot TPL/SPL and load that over USB instead, removing the need for the extra pack step.

[sjoerdsimons]

Adding seperate commands to directly write to the 471/472 (or any other code, but i've not seem those used) would be rather straight-forward and i'm entirely fine with that. useful for experimentation ..

Keep in mind that it's not very user-friendly though; e.g. for some RK35xx boards you need to upload 2 blobs to 471 ("usbhead", TPL/ddr training) and then the SPL to 472 -- So it would be nicer if upstream u-boot could also generate a rockchip compatible boot file similar to how it these days generates a single rockchip image to flash to spi/emmc as well with the lot bundled

[dsx724]

I'm going to try to rework u-boot to generate the proper files. Just to check to make sure my understanding is correct.

1. u-boot's TPL brings up DRAM and then goes back to BootROM so we should transfer TPL to DRAM via 471.
2. transfer SPL and atf/u-boot ITB to DRAM via 472 and execute the SPL: copy the SPL and ITB to somewhere in DRAM, have SPL detect that it was loaded over USB or just try DRAM before SPI/MMC

If there's something I didn't think of or if there's a less intrusive way, please let me know.

[dsx724]

For those interested in booting to RAM, you need modifications like this: libre-computer-project/libretech-u-boot@508b23f