On Thu, 11 Jun 2009, Oliver Neukum wrote: > Am Donnerstag, 11. Juni 2009 17:22:06 schrieb Alan Stern: > > > > Okay, I'll agree to that. It should be made clear that a device which > > > > is "suspended" according to this definition is not necessarily in a > > > > low-power state. For example, before powering down the link to a disk > > > > drive you might want the drive's suspend method to flush the drive's > > > > cache, but it wouldn't have to spin the drive down. > > > > > > This precludes handling busses that have low power states that are > > > left automatically. If such links are stacked the management of > > > acceptable latencies cannot be left to the busses. > > > An actual example are the link states of USB 3.0 > > > > I don't understand. Can you explain more fully? > > I am talking about the U1 and U2 feature of USB 3.0. > > Or abstractly any power saving state that does autoresume in hardware. > In these cases you know that you can enter a powersaving state that > will add X latency. > > In terms of user space API we'll probably add a way for user space > to specify how much latency may be added for power management's sake. > If busses are stacked the "latency budget" has to be handled at core level. > If furthermore states that allow IO but with additional latency are ignored, > the budget will be calculated wrongly. Okay, fine. What does this have to do with Rafael's work? Why does setting the status to RPM_SUSPENDED even when a device is not in a low-power state preclude handling buses that automatically change their power state? I don't see any connection between Rafael's work and managing latencies, beyond the obvious fact that a device will have a higher latency when it is suspended than when it isn't. 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
