Re: Question about loading bare metal firmware

[Bin Meng]

On Tue, Sep 13, 2022 at 5:39 PM Clément Chigot <chigot@adacore.com> wrote:
>
> Hi all,
>
> I'm wondering if there is an official way to load bare metal software
> within qemu emulations.
> I've seen a lot of people (including us) using -kernel. However, the
> doc seems to imply that the generic loader would be a better approach
> (cf [1]). I know that the compatibility with older Qemus is one of the
> reasons why -kernel is still highly used. I've also seen that the
> reset vector can be initialized automatically by -kernel unlike with
> the generic loader (this is the case with RiscV AFAICT).
> But is there any kind of official recommendation on that topic ?
>
> I'm asking that because a recent change in RiscV Polarfire Soc is
> forcing -dtb to be passed along -kernel. But in case of bare board
> software, -dtb isn't needed (at least in our use case).
> I've a patch that allows "-dtb" to be missing with "-kernel" only if
> "-bios none" is provided. But I'm not sure if this is the right way to
> say "it's a bare board software".
>
> @Bin Meng you're the one that added this -kernel support in PolarFire
> Soc. Thus, is my approach looking good for you or do you have a better
> one in mind ?
>

As Peter said, you probably need to use the generic loader for your
use case. The "-kernel" is mainly for the Linux kernel, or a kernel
with Linux kernel compatible boot protocol. In this case, Linux kernel
won't boot without a proper DTB provided, as QEMU PolarFire machine
does not generate a DTB like other RISC-V machines.

> [1] https://www.qemu.org/docs/master/system/qemu-manpage.html#hxtool-8

Regards,
Bin