Alex Williamson <alex.williamson@xxxxxxxxxx> writes:
> On Thu, 2014-06-12 at 16:12 -0400, Bandan Das wrote:
>> Alex Williamson <alex.williamson@xxxxxxxxxx> writes:
>>
>> > If the PCI core set cfg_size isn't large enough for extended
>> > capabilities, then they're not there. Extended config space may be
>> > inaccessible due to a PCI bridge, in which case cfg_size may be cut
>> > short.
>>
>> Just curious, is this part of the spec or just a convention ? I mean
>> could there be devices with quirks ?
>
> The PCIe bridge spec indicates that PCIe-to-PCI bridges should handle
> extended config accesses as an unsupported request. But as in 78916b00,
> we've seen that's not always the case. This just makes us trust
> PCI-core before the capabilities we find on the device. The current
> quirk in the referenced commit is for a relatively uncommon topology,
> but never rule out that we couldn't have a device quirked to avoid
> touching extended config space too. Thanks,
Ok, Understood, Thanks!
> Alex
>
>> > Signed-off-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
>> > ---
>> > drivers/vfio/pci/vfio_pci_config.c | 13 +++++++++----
>> > 1 file changed, 9 insertions(+), 4 deletions(-)
>> >
>> > diff --git a/drivers/vfio/pci/vfio_pci_config.c b/drivers/vfio/pci/vfio_pci_config.c
>> > index 83cd157..4a62a37 100644
>> > --- a/drivers/vfio/pci/vfio_pci_config.c
>> > +++ b/drivers/vfio/pci/vfio_pci_config.c
>> > @@ -1027,8 +1027,11 @@ static int vfio_cap_len(struct vfio_pci_device *vdev, u8 cap, u8 pos)
>> >
>> > if (PCI_X_CMD_VERSION(word)) {
>> > /* Test for extended capabilities */
>> > - pci_read_config_dword(pdev, PCI_CFG_SPACE_SIZE, &dword);
>> > - vdev->extended_caps = (dword != 0);
>> > + if (pdev->cfg_size > PCI_CFG_SPACE_SIZE) {
>> > + pci_read_config_dword(pdev, PCI_CFG_SPACE_SIZE,
>> > + &dword);
>> > + vdev->extended_caps = (dword != 0);
>> > + }
>> > return PCI_CAP_PCIX_SIZEOF_V2;
>> > } else
>> > return PCI_CAP_PCIX_SIZEOF_V0;
>> > @@ -1041,8 +1044,10 @@ static int vfio_cap_len(struct vfio_pci_device *vdev, u8 cap, u8 pos)
>> > return byte;
>> > case PCI_CAP_ID_EXP:
>> > /* Test for extended capabilities */
>> > - pci_read_config_dword(pdev, PCI_CFG_SPACE_SIZE, &dword);
>> > - vdev->extended_caps = (dword != 0);
>> > + if (pdev->cfg_size > PCI_CFG_SPACE_SIZE) {
>> > + pci_read_config_dword(pdev, PCI_CFG_SPACE_SIZE, &dword);
>> > + vdev->extended_caps = (dword != 0);
>> > + }
>> >
>> > /* length based on version */
>> > if ((pcie_caps_reg(pdev) & PCI_EXP_FLAGS_VERS) == 1)
>> >
>> > --
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