Re: [PATCH 02/10] hw/riscv/virt: Add a switch to enable/disable ACPI

[Bin Meng]

On Mon, Feb 6, 2023 at 8:36 PM Andrew Jones <ajones@ventanamicro.com> wrote:
>
> On Mon, Feb 06, 2023 at 12:18:06PM +0100, Philippe Mathieu-Daudé wrote:
> > On 6/2/23 11:54, Andrea Bolognani wrote:
> > > On Thu, Feb 02, 2023 at 10:22:15AM +0530, Sunil V L wrote:
> > > > +    object_class_property_add(oc, "acpi", "OnOffAuto",
> > > > +                              virt_get_acpi, virt_set_acpi,
> > > > +                              NULL, NULL);
> > > > +    object_class_property_set_description(oc, "acpi",
> > > > +                                          "Enable ACPI");
> > >
> > > The way this works on other architectures (x86_64, aarch64) is that
> > > you get ACPI by default and can use -no-acpi to disable it if
> > > desired. Can we have the same on RISC-V, for consistency?
>
> Default on, with a user control to turn off, can be done with a boolean.
> I'm not sure why/if Auto is needed for acpi. Auto is useful when a
> configuration doesn't support a default setting for a feature. If the
> user hasn't explicitly requested the feature to be on or off, then the
> configuration can silently select what works. If, however, the user
> explicitly chooses what doesn't work, then qemu will fail with an error
> instead.

I have a confusion about "OnOffAuto" vs. "bool" type.

Both "OnOffAuto" vs. "bool" type property can have a default value if
user does not assign a value to it from command line. The default
value is:

- ON_OFF_AUTO_AUTO for "OnOffAuto"
- false for "bool"

But the default value can be overridden in the machine's init
function, like in this patch.

So I am not really sure how these 2 types of properties are different.
Why did we introduce a "OnOffAuto" type, and how is that type supposed
to be used in which scenario?

>
> >
> > -no-acpi rather seems a x86-specific hack for the ISA PC machine, and
> > has a high maintenance cost / burden.
> >
> > If hardware provides ACPI support, QEMU should expose it to the guest.
> >
> > Actually, what is the value added by '-no-acpi'?
>
> IIRC, when booting, at least arm guests, with edk2 and ACPI tables,
> then edk2 will provide the guest ACPI tables instead of DT. To ensure
> we can boot with edk2, but still allow the guest to boot with DT, we
> need a way to disable the generation of ACPI tables.
>

Regards,
Bin