Re: [Xen-devel] [PATCH 5/5] xen: arm: handle PCI DT node ranges and interrupt-map properties

[Julien Grall <julien.grall@xxxxxxxxxx>]

On 18/02/2015 15:05, Julien Grall wrote:
> On 18/02/2015 14:37, Ian Campbell wrote:
> > On Wed, 2015-02-18 at 14:19 +0000, Julien Grall wrote:
> > I think so, and we probably should consider the two cases separately
> > since the right answer could reasonably differ for different resource
> > types.
> >
> > I am reasonably convinced that for MMIO (+IO+CFG space) we should map
> > everything as described by the ranges property of the top most node, it
> > can be considered an analogue to / extension of the reg property of that
> > node.
> Agreed.
>
> > For IRQ I'm not so sure, it's possible that routing the IRQ at
> > pci_add_device time might be better, or fit in better with e.g. the ACPI
> > architecture, but mapping everything described in interrupt-map at start
> > of day is also an option and a reasonably simple one, probably.
> I agree that it's simple. Are we sure that we would be able to get a
> "better" solution later without modifying the kernel?
>
> If not, we may need to keep this solution forever.
>
> > This isn't to do with IPA->PA translations but to do with translations
> > between different PA addressing regimes. i.e. the different addressing
> > schemes of difference busses.
> I meant bus address. The name "intermediate address" was misused, sorry.
>
> > Lets say we have a system with a PCI-ROOT device exposing a PCI bus,
> > which in turn contains a PCI-BRIDGE which for the sake of argument lets
> > say is a PCI-FOOBUS bridge.
> > Lets just consider the MMIO hole for now, but IRQ is basically the same.
> >
> > The ranges property on a node describes a mapping from a "parent"
> > address space into a "child" address space.
> >
> > For PCI-ROOT "parent" is the host physical address space and "child" is
> > the PCI MMIO/IO/CFG address spaces.
> >
> > For PCI-BRIDGE "parent" is the PCI-ROOT's child address space (i.e. PCI
> > MMIO/IO/CFG) and "child" is the FOOBUS address space.
> >
> > The inputs ("parents") of the PCI-BRIDGE ranges property must therefore
> > by definition be valid outputs of the PCI-ROOT ranges property (i.e. be
> > "child" addresses).
> >
> > Therefore if we map all of the input/parent ranges described by
> > PCI-ROOT's ranges property we do not need to recurse further and
> > consider PCI-BRIDGE's ranges property -- we've effectively already dealt
> > with it.
> >
> > Does that make more sense?
> I'm still confused, what prevents the PCI-ROOT device to not be
> connected to another bus?
>
> In device tree format, that would give something like:
>
> / {
>
>    soc {
>       ranges = "...";
>
>       pcie {
>         ranges = "...";
>       }
>    }
> }

Actually the device tree of the x-gene board has something similar.

/ {
  soc {
    ranges;

    pcie {
      ranges = "...";
    }
}

"ranges;" means there is not translation necessary. But nothing prevent 
to have a the property "ranges" set.
Regards,

--
Julien Grall

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