On Fri, 12 Jun 2009, Oliver Neukum wrote: > Am Freitag, 12. Juni 2009 04:16:10 schrieb Alan Stern: > > What tree constraint? You mean that the PM core shouldn't allow > > devices to suspend unless all their children are suspended? Why > > doesn't it still apply? > > Because the hardware doesn't need it. But maybe drivers need it. > > Remember, when Rafael and I say "suspend" here, we don't mean "go to a > > low-power state". We mean "the PM core calls the runtime_suspend > > method". No matter what actions the link hardware may decide to take > > on its own, the PM core will still want to observe the > > all-children-suspended restriction when calling runtime_suspend > > methods. > > No. The core if it insists all children be suspended will not use > the hardware's full capabilities. That isn't what I said. The core does not insist that all children be suspended, i.e., be in a low-power state. It insists only that the children's drivers' runtime_suspend methods have been called. Those methods are not obligated to put the children in a low-power state. > If it leaves such power saving measures to the drivers, latency > accounting will be wrong. > > > > I think there are devices who can be suspended while children are active > > > and devices which can not be. This is an attribute of the device and > > > should be evaluated by the core. > > > > Clearly it should be decided by the driver. Should there be a bit for > > it in the dev_pm_info structure? > > Yes. That would resolve the issue. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
