On Thu, Jul 23, 2015 at 05:12:57PM +0100, 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(). Yes you are right, your log is much clearer. > 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 do not know either I will check again what issues this might trigger (apart from some odd log messages) hopefully they are not reading the bases because they are reassigning them anyway on !PCI_PROBE_ONLY, I hope that's not subtler than that. Actually I noticed on alpha at least, they claim resources only on PCI_PROBE_ONLY and for that to succeed bridge bases must be read before, that may be an explanation but I do not know the reason. > 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. I have no way to test them, that's the reason behind the RFT on this patch, I am uneasy too I do not if anyone can help us test it (maybe adding it to -next can help with that). Please let me know. Thanks ! Lorenzo > > I amended the changelog like this: > > PCI: Call pci_read_bridge_bases() from core instead of arch code > > When we scan a PCI bus, we read PCI-PCI bridge window registers with > pci_read_bridge_bases() so we can validate the resource hierarchy. Most > architectures call pci_read_bridge_bases() from pcibios_fixup_bus(), but > PCI-PCI bridges are not arch-specific, so this doesn't need to be in > arch-specific code. > > Call pci_read_bridge_bases() directly from the PCI core instead of from > arch code. > > For alpha and mips, we now call pci_read_bridge_bases() always; previously > we only called it if PCI_PROBE_ONLY was set. > > [bhelgaas: changelog] > Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@xxxxxxx> > Signed-off-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx> > ... > -- 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
