On Wednesday, 1 August 2007 19:35, Alan Stern wrote: > On Wed, 1 Aug 2007, Cornelia Huck wrote: > > > On Wed, 1 Aug 2007 11:22:12 -0400 (EDT), > > Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > > > > > As it stands right now, every place device_move() gets called is > > > already special! > > > > The "special cases" I was thinking about are those where the order to > > suspend/resume is not covered by a parent/child relationship, but by > > (possibly random) order of registration. I'd have thought the rule "the > > child must be suspended before the parent" was pretty straightforward, > > but... > > So you mean additional requirements, like what I encountered with EHCI. > It's peculiar in that the controller contains a hardware switch which > can literally connect a USB device to a different (companion) > controller, and setting the switch before the companion controller has > been resumed won't work. The correct way to handle this would be to > set the switch later when the USB device is resumed, but that would be > much more awkward. > > I haven't heard of any other cases. Well, that's really exceptional and I have no idea how to handle things like that in a generic way. > > (The whole list based on registration order thing seems a bit fragile > > to me, but I don't know enough of the PM core and suspend/resume in > > general to make a better suggestion :/) > > It hasn't been bad in the past. If A was discovered before B then ipso > facto it is safe to suspend B before suspending A. Likewise, in the > absence of device_move, if A was discovered before B then A cannot > appear below B in the device tree. Of course, this assumes devices are > registered as they are discovered. Which is a weak assupmtion ... Well, we seem to have some examples of possible situations in which the design might not be adequate and that's alarming. Perhaps we should create dpm_active right before the suspend, by really traversing the device tree, when we own all device semaphores and no device objects can be added/removed? Greetings, Rafael -- "Premature optimization is the root of all evil." - Donald Knuth _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
