Re: [Qemu-devel] [PATCH 1/2] PCI-e device multi-function hot-add support

[Cao jin]

Hi, Alex,
    Thanks very much for your quick review and I am sorry for my late 
response.

On 09/10/2015 11:29 PM, Alex Williamson wrote:
> On Thu, 2015-09-10 at 20:12 +0800, Cao jin wrote:
> > Enable PCI-e device multifunction hot, just ensure the function 0
> > added last, then driver will got the notification to scan all the
> > function in the slot.
> >
> > Signed-off-by: Cao jin <address@hidden>
> > ---
> >   hw/pci/pcie.c | 22 +++++++++++++---------
> >   1 file changed, 13 insertions(+), 9 deletions(-)
> >
> > diff --git a/hw/pci/pcie.c b/hw/pci/pcie.c
> > index 6e28985..61ebefd 100644
> > --- a/hw/pci/pcie.c
> > +++ b/hw/pci/pcie.c
> > @@ -249,16 +249,20 @@ void pcie_cap_slot_hotplug_cb(HotplugHandler 
> > *hotplug_dev, DeviceState *dev,
> >           return;
> >       }
> >
> > -    /* TODO: multifunction hot-plug.
> > -     * Right now, only a device of function = 0 is allowed to be
> > -     * hot plugged/unplugged.
> > +    /* To enable multifunction hot-plug, we just ensure the function
> > +     * 0 added last. Until function 0 added, we set the sltsta and
> > +     * inform OS via event notification.
> >        */
> > -    assert(PCI_FUNC(pci_dev->devfn) == 0);
> > -
> > -    pci_word_test_and_set_mask(exp_cap + PCI_EXP_SLTSTA,
> > -                               PCI_EXP_SLTSTA_PDS);
> > -    pcie_cap_slot_event(PCI_DEVICE(hotplug_dev),
> > -                        PCI_EXP_HP_EV_PDC | PCI_EXP_HP_EV_ABP);
> > +    if (!(pci_dev->cap_present & QEMU_PCI_CAP_MULTIFUNCTION) &&
> > +            PCI_FUNC(pci_dev->devfn) > 0) {
>
> The PCI spec is actually not entirely clear about whether each function
> in a multifunction device needs to have the multifunction bit set or if
> only function 0 needs to set it.  From a discovery perspective, a kernel
> should only scan for function 0 and only scan non-zero funcions if
> function 0 reports the multifunction bit set.  Therefore, it doesn't
> particularly matter what non-zero functions report for the multifunction
> bit.  QEMU allows either interpretation (see comment in
> pci_init_multifunction), so this appears to be a new requirement that
> breaks assumptions elsewhere.  Thanks,
>
> Alex
Yes, PCI Spec does not describe it clearly. The if() here, is based on 
the condition like following:

  (qemu) device_add e1000,bus=pb1,id=net1,addr=00.1
  (qemu) device_add e1000,bus=pb1,id=net0,addr=00.0
  PCI: 0.0 indicates single function, but 0.1 is already populated.

Now, we can see the net1 via "info pci" while can`t see net1 in guest 
via "lspci -t", so I think maybe it is not good condition, but no big 
deal, so I use the if() to prevent the condition.

will remove the if() in next version.

> > +        error_setg(errp, "single function device, function number must be 0,"
> > +                "but got %d", PCI_FUNC(pci_dev->devfn));
> > +    } else if (PCI_FUNC(pci_dev->devfn) == 0) {
> > +        pci_word_test_and_set_mask(exp_cap + PCI_EXP_SLTSTA,
> > +                                   PCI_EXP_SLTSTA_PDS);
> > +        pcie_cap_slot_event(PCI_DEVICE(hotplug_dev),
> > +                            PCI_EXP_HP_EV_PDC | PCI_EXP_HP_EV_ABP);
> > +    }
> >   }
> >
> >   void pcie_cap_slot_hot_unplug_request_cb(HotplugHandler *hotplug_dev,
>
>
>
> .

--
Yours Sincerely,

Cao Jin