Re: [PATCH v10 3/7] PCI: reserve bus range for SR-IOV device

Yu Zhao
2009-03-09T08:12:50Z

On Sat, Mar 07, 2009 at 04:20:24AM +0800, Matthew Wilcox wrote:
> On Fri, Feb 20, 2009 at 02:54:44PM +0800, Yu Zhao wrote:
> > +static inline void virtfn_bdf(struct pci_dev *dev, int id, u8 *busnr, u8 *devfn)
> > +{
> > + u16 bdf;
> > +
> > + bdf = (dev->bus->number << 8) + dev->devfn +
> > + dev->sriov->offset + dev->sriov->stride * id;
> > + *busnr = bdf >> 8;
> > + *devfn = bdf & 0xff;
> > +}
>
> I find the interface here a bit clunky -- a function returning void
> while having two OUT parameters. How about this variation on the theme
> (viewers are encouraged to come up with their own preferred
> implementations and interfaces):
>
> static inline __pure u16 virtfn_bdf(struct pci_dev *dev, int id)
> {
> return (dev->bus->number << 8) + dev->devfn + dev->sriov->offset +
> dev->sriov->stride * id;
> }
>
> #define VIRT_BUS(dev, id) (virtfn_bdf(dev, id) >> 8)
> #define VIRT_DEVFN(dev, id) (virtfn_bdf(dev, id) & 0xff)
>
> We rely on GCC to do CSE and not actually invoke virtfn_bdf more than
> once.

Yes, that's a good idea. Will replace that function with macros.