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SubjectRe: [RFT PATCH v3] PCI: move pci_read_bridge_bases to the generic PCI layer
On 07/23/2015 09:12 AM, Bjorn Helgaas wrote:
> On Thu, Jul 09, 2015 at 11:59:16AM +0100, Lorenzo Pieralisi wrote:
>> When a PCI bus is scanned, upon PCI bridge detection the kernel
>> has to read the bridge registers to set-up its resources so that
>> the PCI resource hierarchy can be validated properly.
>>
>> Most if not all architectures read PCI bridge registers in the
>> pcibios_fixup_bus hook, that is called by the PCI generic layer
>> whenever a PCI bus is scanned.
>>
>> Since pci_read_bridge_bases is an arch agnostic operation (and it
>> is carried out on all architectures) it can be moved to the generic
>> PCI layer in order to consolidate code and remove the respective
>> calls from the architectures back-ends.
>>
>> The PCI_PROBE_ONLY flag is not checked before calling
>> pci_read_bridge_buses in the generic layer since reading the bridge
>> bases is not related to resources assignment; this implies that it
>> can be carried out safely on PCI_PROBE_ONLY systems too and should
>> not affect architectures (alpha, mips) that check the PCI_PROBE_ONLY
>> flag before reading the bridge bases.
>>
>> Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
>
> Applied to pci/resource for v4.3, thanks!
>
> The PCI_PROBE_ONLY text seems backward to me: previously alpha and mips
> only called pci_read_bridge_bases() if PCI_PROBE_ONLY was set. After this
> patch, alpha and mips systems that do not set PCI_PROBE_ONLY will also call
> pci_read_bridge_bases().
>
> I really don't know why alpha and mips were like that. It seems backwards.
> It seems like we'd want to know the bridge windows if we were assigning
> things, but they only read them if they were *not* going to assign things.
>
> I'm a little uneasy that we might break some alpha or mips system, since
> there must have been some reason this was done originally. It'd be ideal
> if somebody could test a non-PCI_PROBE_ONLY system. But maybe they're all
> obsolete.
>

For alpha, PCI_PROBE_ONLY is set for two platforms, marvel and titan,
out of ~20. mips sets the flag for 6 platforms out of >25.
Unlikely that those are the only relevant ones.

I could try to run some qemu tests for both architectures, but I have
no idea what to look out for. Ideas, anyone ?

Guenter



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