Re: [PATCH v5 03/16] CXL/PCI: Introduce PCIe helper functions pcie_is_cxl() and pcie_is_cxl_port()

Lukas Wunner
2025-01-15T10:12:45Z

On Tue, Jan 14, 2025 at 09:19:12AM -0600, Bowman, Terry wrote:
> On 1/13/2025 5:49 PM, Ira Weiny wrote:
> > Terry Bowman wrote:
> > > --- a/drivers/pci/pci.c
> > > +++ b/drivers/pci/pci.c
> > > @@ -5036,10 +5036,23 @@ static int pci_dev_reset_slot_function(struct pci_dev *dev, bool probe)
> > >
> > > static u16 cxl_port_dvsec(struct pci_dev *dev)
> > > {
> > > + if (!pcie_is_cxl(dev))
> > > + return 0;
> > > +
> > > return pci_find_dvsec_capability(dev, PCI_VENDOR_ID_CXL,
> > > PCI_DVSEC_CXL_PORT);
> > > }
> > >
> > > +bool pcie_is_cxl_port(struct pci_dev *dev)
> > > +{
> > > + 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);
> >
> > Returning bool from a function which returns u16 is odd and I don't think
> > it should be coded this way. I don't think it is wrong right now but this
> > really ought to code the pcie_is_cxl() here and leave cxl_port_dvsec()
> > alone. Calling cxl_port_dvsec(), checking for if the dvsec exists, and
> > returning bool.
>
> Thanks for reviewing. Is this what you are looking for here:
>
> +bool pcie_is_cxl_port(struct pci_dev *dev)
> +{
> + return (cxl_port_dvsec(dev) > 0);

Since cxl_port_dvsec() cannot return a negative integer,
you might as well use:

return !!cxl_port_dvsec(dev);

However last I checked gcc generates code which implicitly turns
a number bigger than 1 into a 1 if the return type is bool.
(I had to fix a bug caused by this behavior once, see 009f8c90f571).

Thanks,

Lukas