Re: [RFC/RFT PATCH 3/6] arm64, numa: Move pcibus_to_node definition to generic numa code

[Bjorn Helgaas <helgaas@kernel.org>]

On Fri, Aug 28, 2020 at 06:11:50PM -0700, Atish Patra wrote:
> On Fri, Aug 28, 2020 at 9:15 AM Bjorn Helgaas <helgaas@kernel.org> wrote:
> > On Fri, Aug 28, 2020 at 10:48:30AM +0100, Jonathan Cameron wrote:
> > > On Fri, 14 Aug 2020 14:47:22 -0700
> > > Atish Patra <atish.patra@wdc.com> wrote:
> > >
> > > > pcibus_to_node is used only when numa is enabled and does not depend
> > > > on ISA. Thus, it can be moved the generic numa implementation.
> > > >
> > > > Signed-off-by: Atish Patra <atish.patra@wdc.com>
> > >
> > > From a more general unification point of view, there seem to
> > > be two ways architectures implement this.
> > > Either
> > >
> > > bus->sysdata.node
> > >
> > > Or as here.
> > > There are weird other options, but let us ignore those :)
> > >
> > > That is going to take a bit of unwinding should we
> > > want to take this unification further and perhaps we want to think
> > > about doing this in pci generic code rather than here?
> > >
> > > Perhaps this is one we are better keeping architecture specific for
> > > now?
> > >
> > > +CC Bjorn and Linux-pci
> > >
> > >
> > > > ---
> > > >  arch/arm64/kernel/pci.c  | 10 ----------
> > > >  drivers/base/arch_numa.c | 11 +++++++++++
> > > >  2 files changed, 11 insertions(+), 10 deletions(-)
> > > >
> > > > diff --git a/arch/arm64/kernel/pci.c b/arch/arm64/kernel/pci.c
> > > > index 1006ed2d7c60..07c122946c11 100644
> > > > --- a/arch/arm64/kernel/pci.c
> > > > +++ b/arch/arm64/kernel/pci.c
> > > > @@ -54,16 +54,6 @@ int raw_pci_write(unsigned int domain, unsigned int bus,
> > > >     return b->ops->write(b, devfn, reg, len, val);
> > > >  }
> > > >
> > > > -#ifdef CONFIG_NUMA
> > > > -
> > > > -int pcibus_to_node(struct pci_bus *bus)
> > > > -{
> > > > -   return dev_to_node(&bus->dev);
> > > > -}
> > > > -EXPORT_SYMBOL(pcibus_to_node);
> > > > -
> > > > -#endif
> > > > -
> > > >  #ifdef CONFIG_ACPI
> > > >
> > > >  struct acpi_pci_generic_root_info {
> > > > diff --git a/drivers/base/arch_numa.c b/drivers/base/arch_numa.c
> > > > index 83341c807240..4ab1b20a615d 100644
> > > > --- a/drivers/base/arch_numa.c
> > > > +++ b/drivers/base/arch_numa.c
> > > > @@ -11,6 +11,7 @@
> > > >  #include <linux/acpi.h>
> > > >  #include <linux/memblock.h>
> > > >  #include <linux/module.h>
> > > > +#include <linux/pci.h>
> > > >  #include <linux/of.h>
> > > >
> > > >  #ifdef CONFIG_ARM64
> > > > @@ -60,6 +61,16 @@ EXPORT_SYMBOL(cpumask_of_node);
> > > >
> > > >  #endif
> > > >
> > > > +#ifdef CONFIG_PCI
> > > > +
> > > > +int pcibus_to_node(struct pci_bus *bus)
> > > > +{
> > > > +   return dev_to_node(&bus->dev);
> > > > +}
> > > > +EXPORT_SYMBOL(pcibus_to_node);
> > > > +
> > > > +#endif
> >
> > I certainly agree that this should not be arch-specific, but I'm not
> > really in favor of adding this PCI gunk in drivers/base.
> >
> > I think we can do better (eventually) by getting rid of
> > pcibus_to_node() completely.  It's not used very much except by
> > cpumask_of_pcibus(), which itself is hardly used at all.
> >
> I am a bit confused here. A quick grep suggested that pcibus_to_node()
> is also called from generic pci probe,
> controller and few drivers(block, infiniband) as well. Maybe I am
> missing something here ?

I didn't say it was *only* used by cpumask_of_pcibus().  13 of the 29
calls are from cpumask_of_pcibus().

As you point out, there are a few drivers that use it.  They typically
have a pci_dev, so they do the equivalent of pcibus_to_node(pdev->bus).
That seems silly; they should just do dev_to_node(&pdev->dev) instead.

I looked at this once, and it seems like there might have been a
wrinkle like the pdev->dev node not being set correctly or something.
If that's the case, I think it should be fixed.

> We can move the pcibus_to_node to arch specific code for now if that's
> what is preferred.

Now I'm the one who's confused :)  Most arches, including arm64,
already have arch-specific implementations of pcibus_to_node().  I
didn't look at the rest of the series to see if there's a reason you
need to move pcibus_to_node() from arch/arm64/kernel/pci.c to
drivers//base/arch_numa.c.  If you don't need to, I would just leave
it where it is.

> > > >  static void numa_update_cpu(unsigned int cpu, bool remove)
> > > >  {
> > > >     int nid = cpu_to_node(cpu);

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