Re: [PATCH 3/6] pci, thunder: Add PCIe host controller devicetree bindings

[Liviu Dudau <Liviu.Dudau@arm.com>]

On Wed, Oct 08, 2014 at 09:49:27AM +0100, Robert Richter wrote:
> On 07.10.14 16:01:49, Liviu Dudau wrote:
> > On Tue, Oct 07, 2014 at 03:27:44PM +0100, Robert Richter wrote:
> > > On 24.09.14 18:06:04, Arnd Bergmann wrote:
> > > > > +               compatible = "cavium,thunder-pcie";
> > > > > +               device_type = "pci";
> > > > > +               msi-parent = <&its>;
> > > > > +               bus-range = <0 255>;
> > > > > +               #size-cells = <2>;
> > > > > +               #address-cells = <3>;
> > > > > +               reg = <0x8480 0x00000000 0 0x10000000>;  /* Configuration space */
> > > > > +               ranges = <0x03000000 0x8010 0x00000000 0x8010 0x00000000 0x70 0x00000000>, /* mem ranges */
> > > > > +                       <0x03000000 0x8300 0x00000000 0x8300 0x00000000 0x80 0x00000000>,
> > > > > +                       <0x03000000 0x87e0 0x00000000 0x87e0 0x00000000 0x01 0x00000000>;
> > > > > +        };
> > > > 
> > > > If you claim the entire 0-255 bus range, I think you should also
> > > > specify a domain, otherwise it's not predictable which domain you
> > > > get.
> > > 
> > > Liviu's code assigns a unique id to the domain if missing, see
> > > of_pci_get_domain_nr(). So I don't think we need to add a "pci-domain"
> > > property here.
> > 
> > Not anymore! That function is gone in v12 onwards. What is in -next has
> > a new function called of_get_pci_domain_nr() (slight name change) but
> > that only gets the value set in the "linux,pci-domain" property of the
> > device node. It is the choice of the host bridge driver to use that
> > function or to use pci_get_new_domain_nr() which *does* generate an
> > unique id every time it gets called.
> 
> I am quite confused a bit on which is the latest code base now. I was
> looking into Bjorn's pci/host-generic and there is a different
> implemetation:
> 
> ----
> /**
>  * This function will try to obtain the host bridge domain number by
>  * using of_alias_get_id() call with "pci-domain" as a stem.  If that
>  * fails, a local allocator will be used.  The local allocator can
>  * be requested to return a new domain_nr if the information is missing
>  * from the device tree.
>  *
>  * @node: device tree node with the domain information
>  * @allocate_if_missing: if DT lacks information about the domain nr,
>  * allocate a new number.
>  *
>  * Returns the associated domain number from DT, or a new domain number
>  * if DT information is missing and @allocate_if_missing is true.  If
>  * @allocate_if_missing is false then the last allocated domain number
>  * will be returned.
>  */
> int of_pci_get_domain_nr(struct device_node *node, bool allocate_if_missing)
> {
>         int domain;
> 
>         domain = atomic_read(&of_domain_nr);
>         if (domain == -1) {
>                 /* first run, get max defined domain nr in device tree */
>                 domain = of_get_max_pci_domain_nr();
>                 /* then set the start value for allocator to be max + 1 */
>                 atomic_set(&of_domain_nr, domain + 1);
>         }
>         domain = of_alias_get_id(node, "pci-domain");
>         if (domain == -ENODEV) {
>                 domain = atomic_read(&of_domain_nr);
>                 if (allocate_if_missing)
>                         atomic_inc(&of_domain_nr);
>         }
> 
>         return domain;
> }
> EXPORT_SYMBOL_GPL(of_pci_get_domain_nr);
> ----
> 
> This differs also from v13. Please check.

I'm not sure what you are looking at. Commit 41e5c0f81d3e does look like
my v13. Not sure why you are still seeing this v11 version.


> 
> It would be good to have a stable code base to work with, so I would
> prefer incremental patches on top of Bjorn's pci/host-generic.

Agreed, but from what I can see from my side pci/host-generic and next
have the same versions, so there should not be any confusion.

Best regards,
Liviu

> 
> > > Liviu's DT implementation that assigns a unique number differs a bit
> > > from ACPI which states: "If _SEG [aka domain number] does not exist,
> > > OSPM assumes that all PCI bus segments are in PCI Segment Group 0."
> > > 
> > > Maybe of_pci_get_domain_nr() should be similar to ACPI. If there are
> > > multiple root bridges, the "pci-domain" property could be forced
> > > instead.
> > 
> > Indeed. But the enforcing is left as an exercise to the host bridge
> > implementor for the moment.
> 
> Right, can be added later.
> 
> Thanks,
> 
> -Robert
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