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

[Gerd Hoffmann]

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?
> 
> -no-acpi rather seems a x86-specific hack for the ISA PC machine, and
> has a high maintenance cost / burden.

Under the hood it is actually a OnOffAuto machine property and -no-acpi
is just a shortcut to set that.

> Actually, what is the value added by '-no-acpi'?

On arm(64) the linux kernel can use either device trees or ACPI to find
the hardware.  Historical reasons mostly, when the platform started
there was no ACPI support.  Also the edk2 firmware uses Device Trees
for hardware discovery, likewise for historical reasons.

When ACPI is available for a platform right from the start I see little
reason to offer an option to turn it off though ...

take care,
  Gerd