On Wed, Jun 12, 2019 at 12:58:17PM -0600, Alex Williamson wrote:
> On Wed, 12 Jun 2019 11:41:36 -0700
> sathyanarayanan kuppuswamy <sathyanarayanan.kuppusw...@linux.intel.com>
> wrote:
>
> > On 6/12/19 11:19 AM, Alex Williamson wrote:
> > > On Wed, 12 Jun 2019 10:06:47 -0700
> > > sathyanarayanan.kuppusw...@linux.intel.com wrote:
> > >
> > >> From: Kuppuswamy Sathyanarayanan
> > >> <sathyanarayanan.kuppusw...@linux.intel.com>
> > >>
> > >> Commit 975bb8b4dc93 ("PCI/IOV: Use VF0 cached config space size for
> > >> other VFs") calculates and caches the cfg_size for VF0 device before
> > >> initializing the pcie_cap of the device which results in using incorrect
> > >> cfg_size for all VF devices > 0. So set pcie_cap of the device before
> > >> calculating the cfg_size of VF0 device.
> > >>
> > >> Fixes: 975bb8b4dc93 ("PCI/IOV: Use VF0 cached config space size for
> > >> other VFs")
> > >> Cc: Ashok Raj <ashok....@intel.com>
> > >> Suggested-by: Mike Campin <mike.cam...@intel.com>
> > >> Signed-off-by: Kuppuswamy Sathyanarayanan
> > >> <sathyanarayanan.kuppusw...@linux.intel.com>
> > >> ---
> > >>
> > >> Changes since v1:
> > >> * Fixed a typo in commit message.
> > >>
> > >> drivers/pci/iov.c | 1 +
> > >> 1 file changed, 1 insertion(+)
> > >>
> > >> diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c
> > >> index 3aa115ed3a65..2869011c0e35 100644
> > >> --- a/drivers/pci/iov.c
> > >> +++ b/drivers/pci/iov.c
> > >> @@ -160,6 +160,7 @@ int pci_iov_add_virtfn(struct pci_dev *dev, int id)
> > >> virtfn->device = iov->vf_device;
> > >> virtfn->is_virtfn = 1;
> > >> virtfn->physfn = pci_dev_get(dev);
> > >> + virtfn->pcie_cap = pci_find_capability(virtfn, PCI_CAP_ID_EXP);
> > >>
> > >> if (id == 0)
> > >> pci_read_vf_config_common(virtfn);
> > > Why not re-order until after we've setup pcie_cap?
> > >
> > > https://lore.kernel.org/linux-pci/20190604143617.0a226...@x1.home/T/#
> >
> > pci_read_vf_config_common() also caches values for properties like
> > class, hdr_type, susbsystem_vendor/device. These values are read/used in
> > pci_setup_device(). So if we can use cached values in
> > pci_setup_device(), we don't have to read them from registers twice for
> > each device.
>
> Sorry, I missed that dependency, a bit too subtle. It's still pretty
> ugly that pci_setup_device()->set_pcie_port_type() is the canonical
> location for setting pcie_cap and now we need to kludge it earlier.
> What about the question in the self follow-up to my patch in the link
> above, can we simply assume 4K config space on a VF? Thanks,
There should be no issue simply reading them once? I don't know
what that exact optimization saves, unless some broken VFs didn't
actually expose all the capabilities in config space and this happens
to workaround the problem.
+ Karim
Cheers,
Ashok
