Re: [PATCH] arm64: acpi: Support PCI devices numa_node property in ACPI mode

[Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>]

On Sat, Apr 08, 2017 at 01:17:32PM -0400, Sinan Kaya wrote:
> On 12/31/1969 7:00 PM, linux-arm-kernel [mailto:linux-arm-kernel-bounces@lists.infradead.org] On Behalf Of Sergey Temerkhanov wrote:
> >  int pcibus_to_node(struct pci_bus *bus)  {
> > -	return dev_to_node(&bus->dev);
> > +	struct pci_config_window *cfg = bus->sysdata;
> > +	struct acpi_device *adev = NULL;
> > +	struct device *dev;
> > +
> > +	if (!acpi_disabled)
> > +		adev = to_acpi_device(cfg->parent);
> > +
> 
> I see a problem here that NUMA node information is read from the
> parent device.  PCI bus can have multiple levels of switches and
> bridges. The NUMA information is only present on the host bridge.
> 
> This code only works if the endpoint is directly connected to the root
> port. 

That's not what this code does. This code retrieves the struct device
backing the ACPI device representing the PNP0A08 host bridge and its
dev->numa_node value (that was set in pci_acpi_scan_root()).

I am not a big fan of this. I wonder if we could not make it DT/ACPI
agnostic by simply setting the numa_node in the pci_bus->dev field,
and propagate it downstream a PCI hierarcy (as we do with sysdata)
in pci_alloc_child_bus().

This way pcibus_to_node() would become straightforward (ie as it
is now - provided the above is doable):

dev_to_node(&bus->dev);

This is suspiciously similar to the domain number song and dance
except that the NUMA node now is in the struct pci_bus->dev->numa_node
instead of struct pci_bus->domain_nr.

Lorenzo