Re: [PATCH v2] PCI: Do not attempt to set ExtTag for VFs

[yanjun.zhu]

On 12/1/25 11:56 PM, Haakon Bugge wrote:
> > On 12 Nov 2025, at 10:54, Håkon Bugge <Haakon.Bugge@xxxxxxxxxx> wrote:
> >
> > The bit for enabling extended tags is Reserved and Preserved (RsvdP)
> > for VFs, according to PCIe r7.0 section 7.5.3.4 table 7.21.  Hence,
> > bail out early from pci_configure_extended_tags() if the device is a
> > VF.


enabling extended tags in PCIe r7.0 section 7.5.3.4 table 7.21 is as below:
"
Extended Tag Field Enable - This bit, in combination with the 10-Bit Tag 
Requester Enable bit and the 14-Bit Tag Requester Enable bit, determines 
how many Tag field bits a Requester is permitted to use for non-UIO 
Requests. This bit is not applicable to a Requester when generating UIO 
Requests. The following applies when the 10-Bit Tag Requester Enable bit 
and the 14-Bit Tag Requester Enable bit are both Clear. If the Extended 
Tag Field Enable bit is Set, the Function is permitted to use an 8-bit 
Tag field as a Requester. If the bit is Clear, the Function is 
restricted to using a 5-bit Tag field. See § Section 2.2.6.2 for 
required behavior when one or both of these larger-Tag Requester Enable 
bits are Set. If software changes the value of the Extended Tag Field 
Enable bit while the Function has outstanding Non-Posted Requests, the 
result is undefined. Functions that do not implement this capability 
hardwire this bit to 0b. Default value of this bit is implementation 
specific.
"

Thus,
Reviewed-by: Zhu Yanjun <yanjun.zhu@xxxxxxxxx>

Zhu Yanjun

> > Otherwise, we may see incorrect log messages such as:
> >
> >    kernel: pci 0000:af:00.2: enabling Extended Tags
> >
> > (af:00.2 is a VF)
> >
> > Fixes: 60db3a4d8cc9 ("PCI: Enable PCIe Extended Tags if supported")
> > Signed-off-by: Håkon Bugge <haakon.bugge@xxxxxxxxxx>
>
> A gentle ping on this one.
>
>
> Thxs, Håkon
>
> > ---
> >
> > v1 -> v2: Added ref to PCIe spec
> > ---
> > drivers/pci/probe.c | 3 ++-
> > 1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> > index 0ce98e18b5a87..014017e15bcc8 100644
> > --- a/drivers/pci/probe.c
> > +++ b/drivers/pci/probe.c
> > @@ -2244,7 +2244,8 @@ int pci_configure_extended_tags(struct pci_dev *dev, void *ign)
> > u16 ctl;
> > int ret;
> >
> > - if (!pci_is_pcie(dev))
> > + /* PCI_EXP_DEVCTL_EXT_TAG is RsvdP in VFs */
> > + if (!pci_is_pcie(dev) || dev->is_virtfn)
> > return 0;
> >
> > ret = pcie_capability_read_dword(dev, PCI_EXP_DEVCAP, &cap);
> > --
> > 2.43.5