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

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Message-ID: <17be8c41-8989-f1da-a843-30f0761f42de@linux.ibm.com>
Date:   Thu, 13 Aug 2020 14:34:12 +0200
From:   Niklas Schnelle <schnelle@...ux.ibm.com>
To:     "Oliver O'Halloran" <oohall@...il.com>
Cc:     Matthew Rosato <mjrosato@...ux.ibm.com>,
        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 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!

> 
> ... snip ...
>