On Wed, Oct 28, 2015 at 02:46:50PM -0700, Alexander Duyck wrote:
> On 10/28/2015 11:43 AM, Bjorn Helgaas wrote:
> >On Wed, Oct 28, 2015 at 11:32:16AM -0500, Bjorn Helgaas wrote:
> >Here's my new proposal:
> >
> > static int compute_max_vf_buses(struct pci_dev *dev)
> > {
> > struct pci_sriov *iov = dev->sriov;
> > int nr_virtfn, busnr, rc = 0;
> >
> > for (nr_virtfn = iov->total_VFs; nr_virtfn; nr_virtfn--) {
> > pci_iov_set_numvfs(dev, nr_virtfn);
> > if (!iov->offset || (nr_virtfn > 1 && !iov->stride)) {
> > rc = -EIO;
> > goto out;
> > }
> >
> > busnr = pci_iov_virtfn_bus(dev, nr_virtfn - 1);
> > if (busnr > iov->max_VF_buses)
> > iov->max_VF_buses = busnr;
> > }
> >
> > out:
> > pci_iov_set_numvfs(dev, 0);
> > return rc;
> > }
> >
>
> This looks good to me. In theory you could save yourself a pair of
> MMIO reads at the end of the loop by just writing numvfs without the
> offset and stride read, but this should work.
True. It's called once per device at boot-time, so it's not a hot path,
and I think it's worth two unnecessary MMIO reads to make it easier to
analyze: there's exactly one place that updates PCI_SRIOV_NUM_VF, and that
place always updates our caches of PCI_SRIOV_VF_OFFSET and
PCI_SRIOV_VF_STRIDE.
Bjorn
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