Re: [PATCH 1/2] PCI/IOV: Add function to allow Function Dependency Link override.

[David Daney]

On 08/22/2016 07:36 AM, Bjorn Helgaas wrote:
> Hi David & Omer,
>
> On Fri, Aug 19, 2016 at 03:32:12PM -0700, Omer Khaliq wrote:
> > From: David Daney <david.daney@xxxxxxxxxx>
> >
> > Some hardware presents an incorrect SR-IOV Function Dependency Link,
> > add a function to allow this to be overridden in the PF driver for
> > such devices.
> >
> > Signed-off-by: David Daney <david.daney@xxxxxxxxxx>
> > Signed-off-by: Omer Khaliq <okhaliq@xxxxxxxxxxxxxxxxxx>
> > ---
> >   drivers/pci/iov.c   | 14 ++++++++++++++
> >   include/linux/pci.h |  1 +
> >   2 files changed, 15 insertions(+)
> >
> > diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c
> > index 2194b44..81f0672 100644
> > --- a/drivers/pci/iov.c
> > +++ b/drivers/pci/iov.c
> > @@ -640,6 +640,20 @@ int pci_enable_sriov(struct pci_dev *dev, int nr_virtfn)
> >   EXPORT_SYMBOL_GPL(pci_enable_sriov);
> >
> >   /**
> > + * pci_sriov_fdl_override - fix incorrect Function Dependency Link
> > + * @dev: the PCI device
> > + * @fdl: the corrected Function Dependency Link value
> > + *
> > + * For hardware presenting an incorrect Function Dependency Link in
> > + * the SR-IOV Extended Capability, allow a driver to override it.
> > + */
> > +void pci_sriov_fdl_override(struct pci_dev *dev, u8 fdl)
> > +{
> > +	dev->sriov->link = fdl;
> > +}
> > +EXPORT_SYMBOL_GPL(pci_sriov_fdl_override);
>
> We usually use quirks to work around problems in config space.  That's
> a nice mechanism because we don't have to add new PCI core interfaces
> and it makes it clear that we're working around a hardware problem.
>
> Can you use a quirk here?  We allocate dev->sriov in the
> pci_init_capabilities() path, so it looks like a pci_fixup_final quirk
> should work.

The struct pci_sriov definition is private to drivers/pci, so in order 
to use a quirk to fix this, we would have to put it in 
drivers/pci/quirks.c.  I was trying to keep this very device specific 
code in the driver, which requires an accessor to be able to manipulate 
the dev->sriov->link field.

If you prefer a quirk in drivers/pci/quirks.c, we can certainly do that 
instead.

Thanks for taking the time to look at this,
David Daney




> > +
> > +/**
> >    * pci_disable_sriov - disable the SR-IOV capability
> >    * @dev: the PCI device
> >    */
> > diff --git a/include/linux/pci.h b/include/linux/pci.h
> > index 2599a98..da8a5b3 100644
> > --- a/include/linux/pci.h
> > +++ b/include/linux/pci.h
> > @@ -1823,6 +1823,7 @@ int pci_num_vf(struct pci_dev *dev);
> >   int pci_vfs_assigned(struct pci_dev *dev);
> >   int pci_sriov_set_totalvfs(struct pci_dev *dev, u16 numvfs);
> >   int pci_sriov_get_totalvfs(struct pci_dev *dev);
> > +void pci_sriov_fdl_override(struct pci_dev *dev, u8 fdl);
> >   resource_size_t pci_iov_resource_size(struct pci_dev *dev, int resno);
> >   #else
> >   static inline int pci_iov_virtfn_bus(struct pci_dev *dev, int id)
> > --
> > 1.9.1
> >
> > --
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