docs: Add a payload section about coreboot support #116

Signed-off-by: Shawn Chang <citypw@gmail.com>
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Shawn Chang 2019-04-24 17:44:58 +08:00 committed by Anup Patel
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OpenSBI as coreboot payload
==============================
[coreboot](https://www.coreboot.org/) is a free/libre and open source firmware platform support multiple hardware architectures( x86, ARMv7, arm64, PowerPC64, MIPS and RISC-V) and diverse hardware models. In RISC-V world, coreboot currently support HiFive Unleashed with OpenSBI as a payload to boot GNU/Linux:
```
SiFive HiFive unleashed's original firmware boot process:
+-----------+
+------+ +------+ +------+ | BBL |
| MSEL |--->| ZSBL |--->| FSBL |--->| +-------+
+------+ +------+ +------+ | | linux |
+---+-------+
coreboot boot process:
+---------------------------------------------------------------------+
| coreboot |
+------+ +------+ | +-----------+ +----------+ +----------+ +-----------------------+
| MSEL |-->| ZSBL |-->| | bootblock |->| romstage |->| ramstage |->| payload ( OpenSBI) |
+------+ +------+ | +-----------+ +----------+ +----------+ | +-------+ |
| | | linux | |
+---------------------------------------------+-------------+-------+-+
```
The upstreaming work is still in progress. There's a [documentation](https://github.com/hardenedlinux/embedded-iot_profile/blob/master/docs/riscv/hifiveunleashed_coreboot_notes-en.md) about how to build [out-of-tree code](https://github.com/hardenedlinux/coreboot-HiFiveUnleashed) to load OpenSBI.