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

[Andrew Jones]

On Tue, Feb 07, 2023 at 09:50:29AM +0100, Philippe Mathieu-Daudé wrote:
> On 6/2/23 13:56, Gerd Hoffmann 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?
> > > 
> > > -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 ...
> 
> Yeah I concur. There is no point in disabling ACPI on the RISCV virt
> machine IMO.

edk2 will only present DT or ACPI to the guest, not both. However, RISCV
Linux supports both. If we don't offer '-no-acpi' as a way to switch to
DT, then edk2+DT users will need to configure the varstore to select it.
And, since testing needs to be done with both, that varstore change will
need to be added to all the testcases which need DT (or a varstore with
DT already selected will need to be maintained and used by the testsuites)

IMO, the generation of the ACPI tables should be 'on' by default, but then
the, already present, '-no-acpi' command line option should be made
available in order to easily inform edk2 to present DT instead of ACPI.

Thanks,
drew