linux-kernel - Re: [PATCH v2] PCI: Introduce flag for detached virtual functions

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Date:   Thu, 13 Aug 2020 09:11:20 -0400
From:   Matthew Rosato <mjrosato@...ux.ibm.com>
To:     Niklas Schnelle <schnelle@...ux.ibm.com>,
        "Oliver O'Halloran" <oohall@...il.com>
Cc:     Alex Williamson <alex.williamson@...hat.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>, pmorel@...ux.ibm.com,
        Michael Ellerman <mpe@...erman.id.au>,
        linux-s390@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        KVM list <kvm@...r.kernel.org>,
        linux-pci <linux-pci@...r.kernel.org>,
        Alexey Kardashevskiy <aik@...abs.ru>
Subject: Re: [PATCH v2] PCI: Introduce flag for detached virtual functions

On 8/13/20 8:34 AM, Niklas Schnelle wrote:
> 
> 
> On 8/13/20 12:40 PM, Niklas Schnelle wrote:
>>
>>
>> On 8/13/20 11:59 AM, Oliver O'Halloran wrote:
>>> On Thu, Aug 13, 2020 at 7:00 PM Niklas Schnelle <schnelle@...ux.ibm.com> wrote:
>>>>
>>>>
>>>> On 8/13/20 3:55 AM, Oliver O'Halloran wrote:
>>>>> On Thu, Aug 13, 2020 at 5:21 AM Matthew Rosato <mjrosato@...ux.ibm.com> wrote:
>>>>>> *snip*
>>>>>> diff --git a/arch/s390/pci/pci.c b/arch/s390/pci/pci.c
>>>>>> index 3902c9f..04ac76d 100644
>>>>>> --- a/arch/s390/pci/pci.c
>>>>>> +++ b/arch/s390/pci/pci.c
>>>>>> @@ -581,6 +581,14 @@ int pcibios_enable_device(struct pci_dev *pdev, int mask)
>>>>>>   {
>>>>>>          struct zpci_dev *zdev = to_zpci(pdev);
>>>>>>
>>>>>> +       /*
>>>>>> +        * If we have a VF on a non-multifunction bus, it must be a VF that is
>>>>>> +        * detached from its parent PF.  We rely on firmware emulation to
>>>>>> +        * provide underlying PF details.
>>>>>> +        */
>>>>>> +       if (zdev->vfn && !zdev->zbus->multifunction)
>>>>>> +               pdev->detached_vf = 1;
>>>>>
>>>>> The enable hook seems like it's a bit too late for this sort of
>>>>> screwing around with the pci_dev. Anything in the setup path that
>>>>> looks at ->detached_vf would see it cleared while anything that looks
>>>>> after the device is enabled will see it set. Can this go into
>>>>> pcibios_add_device() or a fixup instead?
>>>>>
>>>>
>>>> This particular check could go into pcibios_add_device() yes.
>>>> We're also currently working on a slight rework of how
>>>> we establish the VF to parent PF linking including the sysfs
>>>> part of that. The latter sadly can only go after the sysfs
>>>> for the virtfn has been created and that only happens
>>>> after all fixups. We would like to do both together because
>>>> the latter sets pdev->is_virtfn which I think is closely related.
>>>>
>>>> I was thinking of starting another discussion
>>>> about adding a hook that is executed just after the sysfs entries
>>>> for the PCI device are created but haven't yet.
>>>
>>> if all you need is sysfs then pcibios_bus_add_device() or a bus
>>> notifier should work
>>
>> So this might go a bit off track but the problem is that
>> on s390 a VF can be disabled and reenabled with disable_slot()/enable_slot().
>> In this case pcibios_bus_add_device() is not called again but
>> the PF/VF link needs to be reestablished.
> 
> Scratch that I must have made some stupid mistake last time I tried
> this, with your suggestion I tried again and it works perfectly
> moving the setup into pcibios_bus_add_device().
> Thank you, this is actually much nicer!
> 

OK, and I can likewise relocate the setting of detached_vf to 
pcibios_bus_add_device().