Re: [PATCH v11 1/9] PCI: Allow per function PCI slots

[Bjorn Helgaas <helgaas@kernel.org>]

On Tue, Mar 24, 2026 at 04:08:28PM -0700, Farhan Ali wrote:
> On 3/24/2026 2:55 PM, Bjorn Helgaas wrote:
> > On Mon, Mar 16, 2026 at 12:15:36PM -0700, Farhan Ali wrote:
> > > On s390 systems, which use a machine level hypervisor, PCI devices are
> > > always accessed through a form of PCI pass-through which fundamentally
> > > operates on a per PCI function granularity. This is also reflected in the
> > > s390 PCI hotplug driver which creates hotplug slots for individual PCI
> > > functions. Its reset_slot() function, which is a wrapper for
> > > zpci_hot_reset_device(), thus also resets individual functions.
> ...

> > >   static ssize_t address_read_file(struct pci_slot *slot, char *buf)
> > >   {
> > > -	if (slot->number == 0xff)
> > > +	if (slot->number == (u16)-1)
> > This "-1" is mentioned in the commit log, but I don't know where it
> > came from.  I guess we must assign -1 as a default somewhere?  Could
> > this be a #define to connect that assignment with this test?
> 
> The -1 is used a placeholder and from what I could tell
> rpaphp_register_slot() would be the only one to use this. Would you prefer
> this to be a #define?

If that's the only place that uses it, I think a #define would help to
match that use with this one.

I hate having to put it in include/linux/pci.h, but it seems like it
would belong next to PCI_SLOT_ALL_DEVICES (which also doesn't need to
be exposed and is only there because it's next to the struct
pci_slot).