On Tue, 2012-11-06 at 10:17 -0500, Alan Stern wrote: > On Tue, 6 Nov 2012, Huang Ying wrote: > > > On Sun, 2012-11-04 at 20:56 -0500, Alan Stern wrote: > > > On Mon, 5 Nov 2012, Huang Ying wrote: > > > > > > > In current runtime PM implementation, the active child count of the > > > > parent device may be decreased if the runtime PM of the child device > > > > is disabled and forbidden. For example, to unbind a PCI driver with a > > > > PCI device, the following code path is possible: > > > > > > > > pci_device_remove > > > > pm_runtime_set_suspended > > > > __pm_runtime_set_status > > > > atomic_add_unless(&parent->power.child_count, -1, 0) > > > > > > > > That is, the parent device may be suspended, even if the runtime PM of > > > > child device is forbidden to be suspended. This violate the rule that > > > > parent is allowed to be suspended only after all its children are > > > > suspended, and may cause issue. > > > > > > This doesn't sound like a correct description of the situation. The > > > rule is not violated. After pm_runtime_set_suspended runs, the child > > > _is_ suspended. Thus there's no reason not to allow the parent to be > > > suspended. > > > > > > The problem -- if there really is one -- is that a driver can put a > > > device into the suspended state by calling pm_runtime_disable followed > > > by pm_runtime_set_suspended, even if the usage count is > 0. > > > > > > I'm not so sure this should count as a problem. Generally devices > > > aren't disabled for runtime PM unless something is wrong. > > > > 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. > 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. Best Regards, Huang Ying > > So I think the rule could be: even if the device is suspended, the > > device can be put into suspended state only if its usage count == 0. In > > this way, we can solve the issue for PCI driver unbound and that looks > > more reasonable. > > You still have not shown that there really is a problem. Do you have > any particular use case in mind? > > Alan Stern > -- 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/
