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

[Alex Williamson <alex.williamson@redhat.com>]

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 <caoj.fnst@cn.fujitsu.com>
> ---
>  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

> +        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,