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

[Sunil V L]

On Tue, Feb 07, 2023 at 11:57:29AM +0800, Bin Meng wrote:
> 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?
> 

I don't know either. Since it is the same property across architectures,
I used the OnOffAuto instead of a bool. 

May be Gerd and other qemu experts can help us to understand better.
https://github.com/qemu/qemu/commit/17e89077b7e3bc1d96540e21ddc7451c3e077049

Thanks,
Sunil