Re: [PATCH v2] hw/riscv: virt: Assume M-mode FW in pflash0 only when "-bios none"

[Andrea Bolognani <abologna@redhat.com>]

On Wed, May 17, 2023 at 02:57:12PM +1000, Alistair Francis wrote:
> On Mon, May 8, 2023 at 9:45 PM Andrea Bolognani <abologna@redhat.com> wrote:
> > > > Taking a step back, what is even the use case for having M-mode code
> > > > in pflash0? If you want to use an M-mode firmware, can't you just use
> > > > -bios instead? In other words, can we change the behavior so that
> > > > pflash being present always mean loading S-mode firmware off it?
>
> It was originally added to support Oreboot (the Rust version of
> Coreboot). The idea was that Oreboot (ROM) would be in flash and then
> go from there.
>
> It also applies to other ROM code that a user might want to test that
> runs before OpenSBI.

Is there a reason why these would have to be loaded into pflash
instead of being passed to -bios? From a quick look at the
documentation for oreboot[1], it looks like they're doing the latter.

Either way, assuming that there's a genuine reason why pflash must be
used, I think the behavior implemented in v1 (pflash0 is M-mode when
-bios none is used, S-mode otherwise) maps very well conceptually,
and results in behavior matching that of other architectures out of
the box. That's good enough for me :) I was just wondering whether we
could keep things even simpler.


[1] https://github.com/oreboot/oreboot/blob/main/src/mainboard/emulation/qemu-riscv/QEMU.md
-- 
Andrea Bolognani / Red Hat / Virtualization