Re: [PATCH v7 0/4] hw/acpi: add indication for i8042 in IA-PC boot flags of the FADT table

[Ani Sinha]

On Mon, Mar 7, 2022 at 3:06 AM Michael S. Tsirkin <mst@redhat.com> wrote:
>
> On Fri, Mar 04, 2022 at 09:10:28PM +0530, Ani Sinha wrote:
> > This can allow the guest OS to determine more easily if i8042 controller
> > is present in the system or not, so it doesn't need to do probing of the
> > controller, but just initialize it immediately, before enumerating the
> > ACPI AML namespace.
> >
> > To allow "flexible" indication, I don't hardcode the bit at location 1
> > as on in the IA-PC boot flags, but try to search for i8042 on the ISA
> > bus to verify it exists in the system.
> >
> > Why this is useful you might ask - this patch allows the guest OS to
> > probe and use the i8042 controller without decoding the ACPI AML blob
> > at all. For example, as a developer of the SerenityOS kernel, I might
> > want to allow people to not try to decode the ACPI AML namespace (for
> > now, we still don't support ACPI AML as it's a work in progress), but
> > still to not probe for the i8042 but just use it after looking in the
> > IA-PC boot flags in the ACPI FADT table.
>
> I wonder how will such a guest work on an existing qemu release then.

I do not know about other such guests but looking at Serenity OS which
is the reason of motivation of this work, it seems to work by sending
commands to the command IO port:

https://github.com/SerenityOS/serenity/blob/455224d4766df886a43c19e9c015533c025d40dd/Kernel/Devices/HID/I8042Controller.cpp#L34

>  do_wait_then_write(I8042Port::Command, I8042Command::ReadConfiguration); 
> result.is_error())
> do_write(I8042Port::Command, I8042Command::TestPS2Controller);

etc.