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 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 command line parameters and it's compatible with the one used in the upstream
Linux kernel. 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
```