On Thu, Jul 23, 2015 at 05:47:44PM +0100, Guenter Roeck wrote: > 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@xxxxxxx> > > > > 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 ? As I replied to Bjorn, I would not expect pci_read_bridge_bases() to be a disruptive operation on !PCI_PROBE_ONLY systems, I will check again alpha and mips code but it is really hard to say, I will inspect the code again to try to figure it out. Thanks ! Lorenzo -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
