On Tue, Nov 06, 2018 at 01:12:42PM -0700, Jon Derrick wrote: > During pci_rescan_bus(), we may encounter new buses and devices which > don't have MPS set for compatibility. Using this path, newly discovered > buses and devices would then require their MPS to be configured after > driver attachment, which may be too late for drivers which do memory > transactions on probe. This definitely looks like something we need to do. Have you tripped over an actual problem? If so, it might be interesting to include a symptom here, e.g., Unsupported Request error for hot-added device, or whatever it is. Can you clarify the "would then require their MPS to be configured" part? Is there some path where we *do* configure MPS after driver attachment? Or is this just a way of saying that "if we don't configure MPS *before* driver attachment, we would have to do it after"? I'm thinking we could simply say something like: During pci_rescan_bus(), we may encounter new devices which haven't had MPS configured. Their MPS must be configured before we make the devices available for driver attachment by calling pci_bus_add_devices(). > This additionally ensures that any pcie_bus_config kernel settings will > be applied to the buses and devices discovered through this path prior > to driver attachment. > > Signed-off-by: Jon Derrick <jonathan.derrick@xxxxxxxxx> > --- > v1: https://patchwork.kernel.org/patch/10642019/ > > drivers/pci/probe.c | 29 +++++++++++++++++++++++++++++ > 1 file changed, 29 insertions(+) > > diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c > index b1c05b5054a0..126cd426b6f2 100644 > --- a/drivers/pci/probe.c > +++ b/drivers/pci/probe.c > @@ -3156,6 +3156,34 @@ unsigned int pci_rescan_bus_bridge_resize(struct pci_dev *bridge) > return max; > } > > +/* > + * Walks the PCI/PCIe tree to find the first instance of a PCIe device and > + * hands off the PCIe bus to pcie_bus_configure_settings to walk the rest. > + */ > +static int pcie_rescan_bus_configure_settings(struct pci_dev *dev, void *data) > +{ > + if (pci_is_pcie(dev)) { > + struct pci_bus *child, *bus = dev->bus; > + > + list_for_each_entry(child, &bus->children, node) > + pcie_bus_configure_settings(child); It looks possible that this could call pcie_bus_configure_settings() a second time for a device that we've already configured. For example, it's legal to call pci_rescan_bus() on an arbitrary bus even if there has been no hot-add event. Is there something that prevents us from touching this already-configured device? *Probably* we would configure it the same way the second time, but a driver is likely already attached to it, and we shouldn't do anything to it. Even if pcie_bus_configure_settings() happens to be idempotent, that seems like it would be hard to verify and keep true indefinitely. Bjorn > + > + return 1; > + } > + return 0; > +} > + > +/** > + * pci_bus_configure_settings - Configure bus settings > + * @bus: PCI/PCIE bus to configure > + * > + * Currently only configures PCIe bus settings related to MPS and MRRS. > + */ > +static void pci_bus_configure_settings(struct pci_bus *bus) > +{ > + pci_walk_bus(bus, pcie_rescan_bus_configure_settings, NULL); > +} > + > /** > * pci_rescan_bus - Scan a PCI bus for devices > * @bus: PCI bus to scan > @@ -3171,6 +3199,7 @@ unsigned int pci_rescan_bus(struct pci_bus *bus) > > max = pci_scan_child_bus(bus); > pci_assign_unassigned_bus_resources(bus); > + pci_bus_configure_settings(bus); > pci_bus_add_devices(bus); > > return max; > -- > 2.14.4 >
