On Thu, Nov 14, 2024 at 10:45:39AM -0600, Bowman, Terry wrote:
> On 11/14/2024 9:45 AM, Lukas Wunner wrote:
> > On Wed, Nov 13, 2024 at 03:54:17PM -0600, Terry Bowman wrote:
> > > --- a/drivers/pci/pci.c
> > > +++ b/drivers/pci/pci.c
> > > @@ -5038,6 +5038,20 @@ static u16 cxl_port_dvsec(struct pci_dev *dev)
> > > PCI_DVSEC_CXL_PORT);
> > > }
> > >
> > > +bool pcie_is_cxl_port(struct pci_dev *dev)
> > > +{
> > > + if (!pcie_is_cxl(dev))
> > > + return false;
> > > +
> > > + if ((pci_pcie_type(dev) != PCI_EXP_TYPE_ROOT_PORT) &&
> > > + (pci_pcie_type(dev) != PCI_EXP_TYPE_UPSTREAM) &&
> > > + (pci_pcie_type(dev) != PCI_EXP_TYPE_DOWNSTREAM))
> > > + return false;
> > > +
> > > + return cxl_port_dvsec(dev);
> > > +}
> > > +EXPORT_SYMBOL_GPL(pcie_is_cxl_port);
> >
> > The "!pcie_is_cxl(dev)" check at the top of the function is identical
> > to the return value "cxl_port_dvsec(dev)". This looks redundant.
> > However one cannot call pci_pcie_type() without first checking
> > pci_is_pcie(). So I'm wondering if the "!pcie_is_cxl(dev)" check
> > is actually erroneous and supposed to be "!pci_is_pcie(dev)"?
> > That would make more sense to me.
>
> I see pcie_is_cxl(dev) is different than cxl_port_dvsec(dev).
> They check different DVSECs.
Ah, sorry, I missed that.
> CXL flexbus DVSEC presence is cached in pci_dev::is_cxl and returned by
> pcie_is_cxl(). This is used for indicating CXL device.
>
> cxl_port_dvsec(dev) returns boolean based on presence of CXL port DVSEC to
> indicate a CXL port device.
>
> I don't believe they are redundant if you consider you can have a CXL
> device that
> is not a CXL port device.
Can you have a CXL port that is not a CXL device?
If not, it would seem to me that checking for Flexbus DVSEC presence
*is* redundant. Or do you anticipate broken devices which lack the
Flexbus DVSEC and that you explicitly want to exclude?
Thanks,
Lukas
