> From: John Baldwin [mailto:j...@freebsd.org]
> Sent: Thursday, April 20, 2017 02:34
> > Can we add the support of "ACPI0004" with the below one-line change?
> >
> >  acpi_sysres_probe(device_t dev)
> >  {
> > -    static char *sysres_ids[] = { "PNP0C01", "PNP0C02", NULL };
> > +    static char *sysres_ids[] = { "PNP0C01", "PNP0C02", "ACPI0004", NULL };
> >
> Hmm, so the role of C01 and C02 is to reserve system resources, though we
> in turn allow any child of acpi0 to suballocate those ranges (since 
> historically
> c01 and c02 tend to allocate I/O ranges that are then used by things like the
> EC, PS/2 keyboard controller, etc.).  From my reading of ACPI0004 in the ACPI
> 6.1 spec it's not quite clear that ACPI0004 is like that?  In particular, it
> seems that 004 should only allow direct children to suballocate?  This
> change might work, but it will allow more devices to allocate the ranges in
>  _CRS than otherwise.
> Do you have an acpidump from a guest system that contains an ACPI0004
> node that you can share?
> John Baldwin

Hi John,
Thanks for the help!

Please see the attached file, which is got by
"acpidump -dt | gzip -c9 > acpidump.dt.gz"

In the dump, we can see the "ACPI0004" node (VMOD) is the parent of
"VMBus" (VMBS). 
It looks the _CRS of ACPI0004 is dynamically generated. Though we can't
see the length of the MMIO range in the dumped asl code, it does have
a 512MB MMIO range [0xFE0000000, 0xFFFFFFFFF].

It looks FreeBSD can't detect ACPI0004 automatically.
With the above one-line change, I can first find the child device 
acpi_sysresource0 of acpi0, then call AcpiWalkResources() to get
the _CRS of acpi_sysresource0, i.e. the 512MB MMIO range.

If you think we shouldn't touch acpi_sysresource0 here, I guess
we can add a new small driver for ACPI0004, just like we added VMBus
driver as a child device of acpi0?

-- Dexuan
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