Re: [PATCH v2 1/1] PCI/IOV: Fix incorrect cfg_size for VF > 0

[sathyanarayanan kuppuswamy]

On 6/12/19 11:19 AM, Alex Williamson wrote:
> On Wed, 12 Jun 2019 10:06:47 -0700
> sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx wrote:
>
> > From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx>
> >
> > 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.raj@xxxxxxxxx>
> > Suggested-by: Mike Campin <mike.campin@xxxxxxxxx>
> > Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx>
> > ---
> >
> > 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/20190604143617.0a226555@xxxxxxx/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.

> Thanks,
> Alex
--
Sathyanarayanan Kuppuswamy
Linux kernel developer