OpenBSI and U-Boot

[Sean Anderson <seanga2@gmail.com>]

On 8/8/20 10:59 AM, Heinrich Schuchardt wrote:
> Hello Anup,
> 
> I have looking at you OpenSBI code firmware/payloads/test_head.S. Here

I think the real start is in firmware/fw_base.S. From there, secondary
harts loop first in _wait_relocate_copy_done, and then in
_wait_for_boot_hart, and then they execute the next stage via
_start_warm and sbi_init.

> like in U-Boot's common/spl/spl_opensbi.c you put all but one hart in to
> an enless loop (hang).

As far as I can tell, U-Boot has all harts execute the next stage when
SMP is enabled. smp_call_function has all harts execute that function.

> 
> When Linux boots via UEFI it will wake up the extra harts after
> ExitBootServices(). So I assume we should define function hang() in
> lib/hang.c as __efi_runtime to avoid seeing it overwritten by the EFI
> payload.
> 
> @Ard:
> Does Linux take care of the hanging harts and redirect them to its own
> routine before SetVirtualAddressMap()? Otherwise anything could happen.
> 
> On the Kendryte K210 we don't have SPL. So we will not boot in the
> sequence SPL->OpenSBI->U-Boot but OpenSBI->U-Boot. Does this imply that
> we have to implement the hart lottery at the entry point of main U-Boot
> in this case?

Isn't the hart lottery already implemented for U-Boot? E.g. around line
100 of arch/riscv/cpu/start.S.

On another note, does Linux support S-Mode NOMMU? I was under the
impression that NOMMU implied M-Mode (or the other way around).

--Sean