Re: [PATCHv3 2/4] pci: allow all bus devices to use the same slot

[Keith Busch <kbusch@kernel.org>]

On Tue, Feb 10, 2026 at 12:00:56PM -0800, dan.j.williams@intel.com wrote:
> Keith Busch wrote:
> 
> > this new feature is 0xfe. This will not clash with any actual slot
> > number since they are limited to 5 bits.
> 
> Can you say a bit more about why other hotplug controller drivers can
> continue to get away with a single device number as a hotplug slot
> target?  For example, would you expect that the ACPI hotplug driver is
> broken if an ARI device is added?

Right, I don't think acpiphp would work correctly for such a device. I
didn't change that out an abundance of caution to not introduce
regressions to platforms I can't readily test.

I've limited this patch to pciehp since that's the only hotplug driver
that hard-codes the "devnr" value to 0, and ensures there's only one
pciehp "hotplug_slot" per bridge. pciehp is uniquely clear that this
patch is safe.

The remaining hotplug_slot users derive devnr and can make additional
hotplug_slots for each device on the bus, so I can't tell if it is safe
to make the others subscribe to this proposed behavior.

> It looks like the goal of this sentinel is to turn all
> pci_try_reset_slot() into pci_try_reset_bus() only for the native PCIe
> hotplug controller, or did I miss a detail?

Yes, pretty much that. Since every device on the subordinate bus belongs
to the same pciehp slot now, we'll get the same locking, notification,
and state restore as what pci_try_reset_bus() does.
 
> > @@ -41,6 +41,10 @@ static ssize_t address_read_file(struct pci_slot *slot, char *buf)
> >  		return sysfs_emit(buf, "%04x:%02x\n",
> >  				  pci_domain_nr(slot->bus),
> >  				  slot->bus->number);
> > +	if (slot->number == PCI_SLOT_ALL_DEVICES)
> > +		return sysfs_emit(buf, "%04x:%02x:00\n",
> > +				  pci_domain_nr(slot->bus),
> > +				  slot->bus->number);
> 
> Why not treat the PCI_SLOT_ALL_DEVICES case the same as the 0xff case?

Just preserving backward compatibility with what this file would show
for pciehp slots prior to this patch.