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

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Message-ID: <1361810245.2975.14.camel@lorien2>
Date:	Mon, 25 Feb 2013 09:37:25 -0700
From:	Shuah Khan <shuah.khan@...com>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
Cc:	dhowells@...hat.com, Joerg Roedel <joro@...tes.org>,
	paulmck@...ux.vnet.ibm.com, linasvepstas@...il.com,
	davej@...hat.com, tglx@...utronix.de, mtk.manpages@...il.com,
	iommu@...ts.linux-foundation.org,
	LKML <linux-kernel@...r.kernel.org>, linux-pci@...r.kernel.org,
	shemminger@...tta.com, jiang.liu@...wei.com, wangyijing@...wei.com,
	shuahkhan@...il.com
Subject: Re: [PATCH 1/4] pci: Add PCI_BUS() and PCI_DEVID() interfaces to
 return bus number and device id

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@...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@...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




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