The SPL port for the Allwinner D1 RISC-V SoC will probably take a while longer than porting U-Boot proper, as none of the relevant drivers are set up for DM in SPL. In the meantime, we are using[1][2] a fork[3] of Allwinner's boot0 loader, which they also call "spl" in their BSP. boot0 uses this TOC1 image format.
The vendor tools for generating TOC1 images require a binary config file generated by their FEX compiler. Instead of trying to support that, I made up a simple human-readable config file format. I didn't see any existing platform-agnostic parser for multi-image containers in mkimage.
I am sending this as RFC because it is only of temporary/limited use. It only works with one specific fork of boot0 which was modified to "behave" (the the original vendor version monkey-patches a custom header inside the U-Boot image during boot). So it will be obsolete once U-Boot SPL is ported. And it is Yet Another Image Format. On the other hand, it does work, and it is currently being used.
[1]: https://linux-sunxi.org/Allwinner_Nezha#U-Boot [2]: https://fedoraproject.org/wiki/Architectures/RISC-V/Allwinner [3]: https://github.com/smaeul/sun20i_d1_spl
Samuel Holland (1): tools: mkimage: Add Allwinner TOC1 support
common/image.c | 1 + include/image.h | 1 + include/sunxi_image.h | 26 ++++ tools/Makefile | 1 + tools/sunxi_toc1.c | 318 ++++++++++++++++++++++++++++++++++++++++++ 5 files changed, 347 insertions(+) create mode 100644 tools/sunxi_toc1.c