Re: [PATCH 1/4] pci: Add PCI_BUS() and PCI_DEVID() interfaces to return bus number and device id

Shuah Khan
2013-02-25T16:37:33Z

On Wed, 2013-02-20 at 18:19 -0700, Bjorn Helgaas wrote:
> On Mon, Feb 11, 2013 at 4:00 PM, Shuah Khan <shuah.khan@hp.com> wrote:
> > pci defines PCI_DEVFN(), PCI_SLOT(), and PCI_FUNC() interfaces, however,
> > it doesn't have interfaces to return PCI bus and PCI device id. Drivers
> > (AMD IOMMU, and AER) implement module specific definitions for PCI_BUS()
> > and AMD_IOMMU driver also has a module specific interface to calculate PCI
> > device id from bus number and devfn.
> >
> > Add PCI_BUS and PCI_DEVID interfaces to return PCI bus number and PCI device
> > id respectively to avoid the need for duplicate definitions in other modules.
> > AER driver code and AMD IOMMU driver define PCI_BUS. AMD IOMMU driver defines
> > an interface to calculate device id from bus number, and devfn pair.
> >
> > Signed-off-by: Shuah Khan <shuah.khan@hp.com>
> > ---
> > include/uapi/linux/pci.h | 4 ++++
> > 1 file changed, 4 insertions(+)
> >
> > diff --git a/include/uapi/linux/pci.h b/include/uapi/linux/pci.h
> > index 3c292bc0..6b2c8b3 100644
> > --- a/include/uapi/linux/pci.h
> > +++ b/include/uapi/linux/pci.h
> > @@ -30,6 +30,10 @@
> > #define PCI_DEVFN(slot, func) ((((slot) & 0x1f) << 3) | ((func) & 0x07))
> > #define PCI_SLOT(devfn) (((devfn) >> 3) & 0x1f)
> > #define PCI_FUNC(devfn) ((devfn) & 0x07)
> > +#define PCI_DEVID(bus, devfn) ((((u16)bus) << 8) | devfn)
> > +
> > +/* return bus from PCI devid = ((u16)bus_number) << 8) | devfn */
> > +#define PCI_BUS(x) (((x) >> 8) & 0xff)
> >
> > /* Ioctls for /proc/bus/pci/X/Y nodes. */
> > #define PCIIOC_BASE ('P' << 24 | 'C' << 16 | 'I' << 8)
>
> David, can you point me at a description of include/uapi ... what is
> there and why, and how we should decide what new things go in
> include/uapi/linux/pci.h as opposed to include/linux/pci.h? Maybe
> there should be something in Documentation/?
>
> I'm guessing it's something to do with being exported to userland, but
> I'm not sure the things in this patch (PCI_DEV_ID, PCI_BUS) are really
> exportable in the sense of being used for syscalls, etc.
>

Bjorn,David,

Looks like the following thread answers some of the questions about when
this uapi export was done on the existing defines.

https://lkml.org/lkml/2011/7/28/198

Sounds like the concern is that the older defines PCI_DEVFN, PCI_SLOT,
PCI_FUNC, and PCI_DEVID could be exported, but not the new ones I
added. I could find any discussion on whether these four older defines
are exportable or the reasons for the export in the above thread.

So the question is if uapi/linux.pci.h isn't the right place, do you
have a recommendation on where they belong. The only alternative I can
think of is include/linux/pci.h. It makes functional and logical sense
to add the new defines to where the existing ones are defines. At least,
not knowing the details of the change that moved PCI_DEVFN etc. to
uapi/pci.h, that is my conclusion.

-- Shuah