Messages in this thread | | | Date | Thu, 23 Jul 2015 09:47:44 -0700 | From | Guenter Roeck <> | Subject | Re: [RFT PATCH v3] PCI: move pci_read_bridge_bases to the generic PCI layer |
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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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