Re: About hotplug multifunction

["Michael S. Tsirkin" <mst@redhat.com>]

On Sun, Sep 11, 2011 at 12:01:49PM -0300, Marcelo Tosatti wrote:
> On Sun, Sep 11, 2011 at 12:23:57PM +0300, Michael S. Tsirkin wrote:
> > On Fri, Sep 09, 2011 at 03:34:26PM -0300, Marcelo Tosatti wrote:
> > > > > something I noted when readin our acpi code:
> > > > > we currently pass eject request for function 0 only:
> > > > >                Name (_ADR, nr##0000)
> > > > > We either need a device per function there (acpi 1.0),
> > > > > send eject request for them all, or use ffff
> > > > > as function number (newer acpi, not sure which version).
> > > > > Need to see which guests (windows,linux) can handle which form.
> > > > 
> > > > I'd guess we need to change that to ffff.
> > > 
> > > No need, only make sure function 0 is there and all other functions
> > > should be removed automatically by the guest on eject notification.
> > 
> > Hmm, the ACPI spec explicitly says:
> > 
> > High word = Device #, Low word = Function #.
> > (e.g., device 3, function 2 is 0x00030002). To refer
> > to all the functions on a device #, use a function
> > number of FFFF).
> 
> Right, but this is the _ADR of the device instance in ACPI. 
> The communication between QEMU and the ACPI DSL code is all 
> based in slots.

It's easy to extend that if we like though.

> > > ACPI PCI hotplug is based on slots, not on functions. It does not
> > > support addition/removal of individual functions.
> > 
> > Interesting. Is this just based on general logic,
> > reading of the linux driver or the ACPI spec?
> 
> Its based on Seabios ACPI DST implementation and its relationship with
> the QEMU implementation in acpi_piix4.c.
> 
> > The ACPI spec itself seems pretty vague. All tables
> > list devices, where each device has an _ADR entry,
> > which is built up of PCI device # and function #.
> 
> Yes, it is vague. Given the mandate from the PCI spec a device _must
> contain_ function 0, usage (including hotplug/unplug) of individual
> functions other than 0 as separate devices is a no-go.

It doesn't seem to be a big issue.
We could, for example, keep a stub function 0 around.

-- 
MST