Re: qemu direct kernel boot on LoongArch

["Thomas Weißschuh" <thomas@t-8ch.de>]

On 2024-09-05 17:18:07+0000, Jason A. Donenfeld wrote:
> On Thu, Sep 5, 2024 at 5:16 PM Thomas Weißschuh <thomas@t-8ch.de> wrote:
> >
> > On 2024-09-05 17:07:22+0000, Jason A. Donenfeld wrote:
> > > On Thu, Sep 5, 2024 at 5:05 PM Thomas Weißschuh <thomas@t-8ch.de> wrote:
> > > >
> > > > On 2024-09-05 16:53:55+0000, Jason A. Donenfeld wrote:
> > > > > On Thu, Sep 05, 2024 at 07:25:05AM +0200, Thomas Weißschuh wrote:
> > > > > > On 2024-09-05 06:04:12+0000, Jason A. Donenfeld wrote:
> > > > > > > On Thu, Sep 5, 2024 at 5:45 AM maobibo <maobibo@loongson.cn> wrote:
> > > > > > > >
> > > > > > > > Jason,
> > > > > > > >
> > > > > > > > With the latest qemu 9.1 version, elf format booting is supported.
> > > > > > >
> > > > > > > Thanks, I just figured this out too, about 4 minutes ago. Excellent.
> > > > > > > And the 1G minimum ram limit is gone too.
> > > > > > >
> > > > > > > Now working on how to trigger resets.
> > > > > >
> > > > > > With "reset" do you mean normal (non-panic) system shutdown/poweroff?
> > > > > > Since QEMU 9.1 and a recent kernel you can use the pvpanic device for
> > > > > > that in a cross-architecture way.
> > > > >
> > > > > What I mean is that I need for userspace calling `reboot(RB_AUTOBOOT);`
> > > > > to actually result in QEMU being told to reboot the system. Sounds like
> > > > > that's not possible (yet?) in 9.1?
> > > >
> > > > With reboot(RB_POWER_OFF) this is indeed the exact usecase for pvpanic
> > >
> > > I'm actually using reboot(RB_AUTOBOOT) wth QEMU's -no-reboot, because
> > > that tends to be far more compatible with a greater number of
> > > platforms, for example, x86 without acpi. Shucks.
> >
> > You can check that both QEMU and the kernel support pvpanic shutdown
> > through sysfs and if so use reboot(RB_POWER_OFF); and
> > reboot(RB_AUTOBOOT) otherwise.
> 
> I guess. But the whole idea is to bloat the code as little as possible
> and use one interface for everything. Pushing that all up into
> userspace is pretty icky.

If it works through ACPI everywhere then sure.

> It sounds like LoongArch already supports this via ACPI GED, but
> there's some plumbing that needs to be done still. So maybe I'll just
> wait for that.

Also sounds reasonable.

> Meanwhile, any idea about adding a second serial to the platform? I've
> been futzing with it for a bit now to no avail.

No idea, sorry.