doc: sifive: fu540: Update QEMU instruction when using U-Boot as the payload

Document that when U-Boot v2020.01 (or higher) is used as the payload,
we need adjust the instructions a little bit when testing OpenSBI with
QEMU 'sifive_u' machine.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Atish Patra <atish.patra@wdc.com>
This commit is contained in:
Bin Meng 2020-02-10 07:42:03 -08:00 committed by Anup Patel
parent 9a717ec12e
commit d6fa7f95bb

View file

@ -183,3 +183,13 @@ same instructions above, with the exception of not passing FW_PAYLOAD_FDT_PATH.
This is because QEMU generates a device tree blob on the fly based on the
command line parameters and it's compatible with the one used in the upstream
Linux kernel.
When U-Boot v2020.01 (or higher) is used as the payload, as the SiFive FU540
DTB for the real hardware is embedded in U-Boot binary itself, due to the same
reason above, we need to switch the U-Boot sifive_fu540_defconfig configuration
from CONFIG_OF_SEPARATE to CONFIG_OF_PRIOR_STAGE so that U-Boot uses the DTB
generated by QEMU, and u-boot.bin should be used as the payload image, like:
```
make PLATFORM=sifive/fu540 FW_PAYLOAD_PATH=<u-boot_build_dir>/u-boot.bin
```