Re: [PATCH v13 10/12] PCI: Assign unassigned bus resources in pci_scan_root_bus()

[Bjorn Helgaas]

On Mon, Sep 29, 2014 at 3:02 PM, Benjamin Herrenschmidt
<benh@xxxxxxxxxxxxxxxxxxx> wrote:
> On Mon, 2014-09-29 at 12:06 -0700, Yinghai Lu wrote:
>> On Mon, Sep 29, 2014 at 11:25 AM, Yinghai Lu <yinghai@xxxxxxxxxx> wrote:
>> > On Mon, Sep 29, 2014 at 7:29 AM, Liviu Dudau <Liviu.Dudau@xxxxxxx> wrote:
>> >> If the firmware has not assigned all the bus resources and we are not just
>> >> probing the PCI buses, it makes sense to assign the unassigned resources
>> >> in pci_scan_root_bus().
>> >>
>> >> Signed-off-by: Liviu Dudau <Liviu.Dudau@xxxxxxx>
>> >> Signed-off-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
>> >> CC: Arnd Bergmann <arnd@xxxxxxxx>
>> >> CC: Jason Gunthorpe <jgunthorpe@xxxxxxxxxxxxxxxxxxxx>
>> >> CC: Rob Herring <robh+dt@xxxxxxxxxx>
>> >> ---
>> >>  drivers/pci/probe.c | 3 +++
>> >>  1 file changed, 3 insertions(+)
>> >>
>> >> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
>> >> index 636d1c9..d2ebd49 100644
>> >> --- a/drivers/pci/probe.c
>> >> +++ b/drivers/pci/probe.c
>> >> @@ -1951,6 +1951,9 @@ struct pci_bus *pci_scan_root_bus(struct device *parent, int bus,
>> >>         if (!found)
>> >>                 pci_bus_update_busn_res_end(b, max);
>> >>
>> >> +       if (!pci_has_flag(PCI_PROBE_ONLY))
>> >> +               pci_assign_unassigned_bus_resources(b);
>> >> +
>> >>         pci_bus_add_devices(b);
>> >>         return b;
>> >>  }
>> >
>> > No, you can not do it that early.
>> >
>> > On x86, we need to call
>> > pcibios_resource_survey_bus at first.
>>
>> on x86:
>> pcibios_init
>> pcibios_resource_survey()
>> pcibios_assign_resources() via fs_initcall
>
> Right and on powerpc and others as well. We need to survey existing
> resources. We also have a number of platform things that might need
> to happen before we do the final re-assignment pass.

That's true today.  But I don't know whether it *has* to be this way
forever.  On x86, pcibios_resource_survey() throws in E820 information
(which we know long before we do any PCI enumeration) and some IO-APIC
resources (it looks like we also know these before PCI enumeration).
Powerpc has pcibios_reserve_legacy_regions(), but that looks like
mostly stuff that could be done when we find the host bridge, before
we enumerate PCI devices below it.

Bjorn
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