> -----Original Message-----
> From: Bin Meng <bmeng.cn@...>
> Sent: 01 April 2020 10:29
> To: Anup Patel <Anup.Patel@...>
> Cc: tech-unixplatformspec@...; Atish Patra
> <Atish.Patra@...>
> Subject: Re: [RISC-V] [tech-unixplatformspec] [PATCH] Add system reboot
> extension
>
> On Tue, Mar 31, 2020 at 12:13 PM Anup Patel <anup.patel@...> wrote:
> >
> > This patch adds SBI v0.2 compliant system reboot extension. It defines
> > two functions:
> > 1. sbi_reboot - A system reboot call with reboot type as parameter 2.
> > sbi_shutdown - A system shutdown/poweroff call
> >
> > The sbi_shutdown function defined here replaces SBI v0.1 shutdown
> > function.
> >
> > Signed-off-by: Atish Patra <atish.patra@...>
> > Signed-off-by: Anup Patel <anup.patel@...>
> > ---
> >  riscv-sbi.adoc | 64
> > ++++++++++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 64 insertions(+)
> >
>
> One generic comment, pretty much similar to the SBI PMP extension I
> proposed, is that why is this necessary to introduce a new SBI extension to
> support reboot and shutdown?
>
> Do these functionalities have to be operated from M-mode?

There are two cases:

1. If a system is partitioned between secure and non-secure world then we
cannot allow non-secure S-mode software to shutdown/reboot the system
without secure S-mode software knowing about it. The SBI shutdown/reboot
calls help M-mode software (OpenSBI) to mediate the shutdown/reboot
request coming from non-secure S-mode software.

2. In virtualization world, we don't have a standard way to shutdown/reboot
Guest/VM across architectures. To tackle this, we generally have architecture
specific hypercall for shutdown/reboot. For RISC-V, we don't want each
hypervisor coming up with its own hypercalls so we standardize these as
SBI calls (This rationale is similar to ARM PSCI shutdown/reboot calls).

Regards,
Anup