RE: Add support for ACPI Module Device ACPI0004?

> From: John Baldwin
> Sent: Thursday, April 27, 2017 00:14
> On Wednesday, April 26, 2017 09:18:48 AM Sepherosa Ziehau wrote:
> > On Wed, Apr 26, 2017 at 4:36 AM, John Baldwin <jhb_at_freebsd.org> wrote:
> > > On Thursday, April 20, 2017 02:29:30 AM Dexuan Cui wrote:
> > >> > From: John Baldwin [mailto:jhb_at_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?
> > >
> > > Hmmm, so looking at this, the "right" thing is probably to have a device
> > > driver for the ACPI0004 device that parses its _CRS and then allows its
> > > child devices to sub-allocate resources from the ranges in _CRS.  However,
> > > this would mean make VMBus be a child of the ACPI0004 device.
> Suppose
> > > we called the ACPI0004 driver 'acpi_module' then the 'acpi_module0'
> device
> > > would need to create a child device for all of its child devices.  Right
> > > now acpi0 also creates devices for them which is somewhat messy (acpi0
> > > creates child devices anywhere in its namespace that have a valid _HID).
> > > You can find those duplicates and remove them during acpi_module0's
> attach
> > > routine before creating its own child device_t devices.  (We associate
> > > a device_t with each Handle when creating device_t's for ACPI handles
> > > which is how you can find the old device that is a direct child of acpi0
> > > so that it can be removed).
> >
> > The remove/reassociate vmbus part seems kinda "messy" to me.  I'd just
> > hook up a new acpi0004 driver, and let vmbus parse the _CRS like what
> > we did to the hyper-v's pcib0.
> 
> The acpi_pci driver used to do the remove/reassociate part.  What acpi0
> should probably be doing is only creating device_t nodes for immediate
> children.  This would require an ACPI-aware isa0 for LPC devices below
> the ISA bus in the ACPI namespace.  We haven't done that in part because
> BIOS vendors are not always consistent in placing LPC devices under an
> ISA bus.  However, you otherwise have no good way to find your parent
> ACPI0004 device.  You could perhaps find your ACPI handle, ask for its
> parent handle, then ask for the device_t of that handle to find the
> ACPI0004 device, but then you'd need to have all your bus_alloc_resource
> calls go to that device, not your "real" parent of acpi0, which means
> you can't use any of the standard bus_alloc_resource() methods like
> bus_alloc_resource_any() but would have to manually use
> BUS_ALLOC_RESOURCE
> with the ACPI0004 device as the explicit first argument.  It is primarily
> the ability to let ACPI0004's driver transparently intercept all the
> resource allocation so it can manage that is the reason for "VMBus"
> to be a child of ACPI0004 rather than its sibling.
> 
> --
> John Baldwin

Hi John,
Thank you for the detailed analysis, but IMHO this seems too complex? :-)

Can we just add a small driver for ACPI0004 like this:
https://reviews.freebsd.org/D10531

This way, we only need to make a small change in VMBus driver reusing
the current code:
https://reviews.freebsd.org/D10532

Looking forward to your comment!

Thanks,
-- Dexuan