On Wednesday, November 07, 2012 10:49:04 AM Alan Stern wrote: > On Wed, 7 Nov 2012, Huang Ying wrote: > > > > > Devices will be disabled if the PCI driver is unbound from the PCI > > > > device. > > > > > > Yes. But without a PCI driver, nothing will call > > > pm_runtime_set_suspended. > > > > pm_runtime_set_suspended will be called in pci_device_remove or error > > path of local_pci_probe. > > Yes, okay. But that's what we want. Unused, driverless PCI devices > shouldn't force their parents to remain at full power. > > > > And even if something does call > > > pm_runtime_set_suspended, it's still not a problem -- the device can't > > > be used without a driver. > > > > The VGA device can be used without a driver. > > Ah, right, that's your _real_ problem. You should have mentioned this > in the original Changelog for the patch. > > Rafael, this does need to be fixed.
Yup. > The PCI subsystem assumes that > driverless devices are not in use, so they are disabled for runtime PM > and marked as suspended. This is not appropriate for VGA devices, > which can indeed be used without a driver. > > I'm not sure what the best solution is. Maybe we should Ying's > proposal a step farther: > > Make pm_runtime_set_suspended() fail if runtime PM is > forbidden. > > Make pm_runtime_forbid() call pm_runtime_set_active() > (and do a runtime resume of the parent) if disable_depth > 0. I'd prefer this one. The callers of pm_runtime_forbid() may actually reasonably expect something like this to happen. > Make the PCI runtime-idle routine call > pm_runtime_set_suspended() if disable_depth > 0. Or maybe > do this for all devices, in the runtime PM core. That would mean calling it on every call to pm_runtime_put() and friends which seems to be a bit wasteful. Thanks, Rafael -- I speak only for myself. Rafael J. Wysocki, Intel Open Source Technology Center. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
