Re: [PATCH] hw/riscv: virt: Enable booting M-mode or S-mode FW from pflash0

[Sunil V L]

On Fri, Apr 21, 2023 at 12:39:46PM +0800, Bin Meng wrote:
> On Fri, Apr 21, 2023 at 12:34 PM Sunil V L <sunilvl@ventanamicro.com> wrote:
> >
> > Currently, virt machine supports two pflash instances each with
> > 32MB size. However, the first pflash is always assumed to
> > contain M-mode firmware and reset vector is set to this if
> > enabled. Hence, for S-mode payloads like EDK2, only one pflash
> > instance is available for use. This means both code and NV variables
> > of EDK2 will need to use the same pflash.
> >
> > The OS distros keep the EDK2 FW code as readonly. When non-volatile
> > variables also need to share the same pflash, it is not possible
> > to keep it as readonly since variables need write access.
> >
> > To resolve this issue, the code and NV variables need to be separated.
> > But in that case we need an extra flash. Hence, modify the convention
> > such that pflash0 will contain the M-mode FW only when "-bios none"
> > option is used. Otherwise, pflash0 will contain the S-mode payload FW.
> > This enables both pflash instances available for EDK2 use.
> >
> > Example usage:
> > 1) pflash0 containing M-mode FW
> > qemu-system-riscv64 -bios none -pflash <mmode_fw> -machine virt
> > or
> > qemu-system-riscv64 -bios none \
> > -drive file=<mmode_fw>,if=pflash,format=raw,unit=0 -machine virt
> >
> > 2) pflash0 containing S-mode payload like EDK2
> > qemu-system-riscv64 -pflash <smode_fw_code> -pflash <smode_vars> -machine  
> > virt
> > or
> > qemu-system-riscv64 -bios <opensbi_fw> \
> > -pflash <smode_fw_code> \
> > -pflash <smode_vars> \
> > -machine  virt
> > or
> > qemu-system-riscv64 -bios <opensbi_fw> \
> > -drive file=<smode_fw_code>,if=pflash,format=raw,unit=0,readonly=on \
> > -drive file=<smode_fw_vars>,if=pflash,format=raw,unit=1 \
> > -machine virt
> 
> Please update the docs in docs/system/riscv/virt.rst to include how to
> run EDK2 bios with these settings.
> 
Thanks Bin. Shall I do it as a separate patch after this gets approved?
The reason is, I need to make changes in EDK2 to work with this. Once
EDK2 changes are also in place, will send a patch to update this
documentation. Does it make sense?

Thanks,
Sunil