On Sun, 2013-09-08 at 00:16 +0200, Rafael J. Wysocki wrote: > From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx> > > In the current ACPIPHP notify handler we always go directly for a > rescan of the parent bus if we get a device check notification for > a device that is not a bridge. However, this obviously is > overzealous if nothing really changes, because this way we may rescan > the whole PCI hierarchy pretty much in vain. > > That happens on Alex Williamson's machine whose ACPI tables contain > device objects that are supposed to coresspond to PCIe root ports, > but those ports aren't physically present (or at least they aren't > visible in the PCI config space to us). The BIOS generates multiple > device check notifies for those objects during boot and for each of > them we go straight for the parent bus rescan, but the parent bus is > the root bus in this particular case. In consequence, we rescan the > whole PCI bus from the top several times in a row, which is > completely unnecessary, increases boot time by 50% (after previous > fixes) and generates excess dmesg output from the PCI subsystem. > > Fix the problem by checking if we can find anything new in the > slot corresponding to the device we've got a device check notify > for and doing nothig if that's not the case. > > The spec (ACPI 5.0, Section 5.6.6) appears to mandate this behavior, > as it says: > > Device Check. Used to notify OSPM that the device either appeared > or disappeared. If the device has appeared, OSPM will re-enumerate > from the parent. If the device has disappeared, OSPM will > invalidate the state of the device. OSPM may optimize out > re-enumeration. > > Therefore, according to the spec, we are free to do nothing if > nothing changes. > > References: https://bugzilla.kernel.org/show_bug.cgi?id=60865 > Reported-by: Alex Williamson <alex.williamson@xxxxxxxxxx> > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx> > --- Works for me. Thanks! Tested-by: Alex Williamson <alex.williamson@xxxxxxxxxx> > On top of linux-pm.git/linux-next. > > Thanks, > Rafael > > --- > drivers/pci/hotplug/acpiphp_glue.c | 32 +++++++++++++++++++++++++------- > 1 file changed, 25 insertions(+), 7 deletions(-) > > Index: linux-pm/drivers/pci/hotplug/acpiphp_glue.c > =================================================================== > --- linux-pm.orig/drivers/pci/hotplug/acpiphp_glue.c > +++ linux-pm/drivers/pci/hotplug/acpiphp_glue.c > @@ -528,6 +528,16 @@ static void check_hotplug_bridge(struct > } > } > > +static int acpiphp_rescan_slot(struct acpiphp_slot *slot) > +{ > + struct acpiphp_func *func; > + > + list_for_each_entry(func, &slot->funcs, sibling) > + acpiphp_bus_add(func_to_handle(func)); > + > + return pci_scan_slot(slot->bus, PCI_DEVFN(slot->device, 0)); > +} > + > /** > * enable_slot - enable, configure a slot > * @slot: slot to be enabled > @@ -544,10 +554,7 @@ static void __ref enable_slot(struct acp > LIST_HEAD(add_list); > int nr_found; > > - list_for_each_entry(func, &slot->funcs, sibling) > - acpiphp_bus_add(func_to_handle(func)); > - > - nr_found = pci_scan_slot(bus, PCI_DEVFN(slot->device, 0)); > + nr_found = acpiphp_rescan_slot(slot); > max = acpiphp_max_busnr(bus); > for (pass = 0; pass < 2; pass++) { > list_for_each_entry(dev, &bus->devices, bus_list) { > @@ -840,11 +847,22 @@ static void hotplug_event(acpi_handle ha > case ACPI_NOTIFY_DEVICE_CHECK: > /* device check */ > dbg("%s: Device check notify on %s\n", __func__, objname); > - if (bridge) > + if (bridge) { > acpiphp_check_bridge(bridge); > - else > - acpiphp_check_bridge(func->parent); > + } else { > + struct acpiphp_slot *slot = func->slot; > + int ret; > > + /* > + * Check if anything has changed in the slot and rescan > + * from the parent if that's the case. > + */ > + mutex_lock(&slot->crit_sect); > + ret = acpiphp_rescan_slot(slot); > + mutex_unlock(&slot->crit_sect); > + if (ret) > + acpiphp_check_bridge(func->parent); > + } > break; > > case ACPI_NOTIFY_EJECT_REQUEST: -- 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
