Re: QEMU RISC-V virt machine poweroff driver

[Anup Patel <anup@brainfault.org>]

On Sat, Nov 16, 2019 at 3:45 AM Nick Kossifidis <mick@ics.forth.gr> wrote:
>
> Στις 2019-11-07 23:24, Christoph Hellwig έγραψε:
> > Hi all,
> >
> > this patch add a driver for the test device in the Qemu RISC-V
> > virt machine which allows properly shutting down the VM.
> > It also is added to the riscv defconfig given that qemu-virt
> > is the most popular riscv platform.
> >
> > _______________________________________________
> > linux-riscv mailing list
> > linux-riscv@lists.infradead.org
> > http://lists.infradead.org/mailman/listinfo/linux-riscv
>
> We do this already through OpenSBI, I contributed a patch for this some
> time ago.
>
> https://github.com/riscv/opensbi/commit/51e543511a7425da1a5378e149de0b45928c7111#diff-36ecc47313ff13e406c53b99471f294e
>
> Last time I checked I could just halt and the system would shut down
> properly.

We only have poweroff SBI call in SBI v0.1 spec.

Also, we had proposed SBI v0.2 SRST extension having both
Poweroff and Reboot SBI calls but before we can have this SBI
extension we need to clarify scope of SBI interface in RISC-V
privilege spec so that we can have system-level SBI calls defined
in SBI spec. In future, we will bring back the proposal for SBI v0.2
SRST extension.

There are two cases in which we might need SOC specific
Poweroff and Reboot drivers in Linux:
1. SBI v0.2 onwards all SBI calls are optional so SOC vendor
can choose to provide explicit driver instead of implementing
SBI calls for Poweroff and Reboot.
2. The M-mode NOMMU Linux does not have SBI interface
so for this case SOC vendors will have to provide explicit
drivers.

If SOC Poweroff and Reboot mechanisms are simple enough
then SOC vendors can straight away use SYSCON Poweroff
and SYSCON Reboot drivers instead of writing it from scratch.

Regards,
Anup

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