On Tue, 15 Dec 2009, Linus Torvalds wrote: > On Tue, 15 Dec 2009, Alan Stern wrote: > > > > Okay. This obviously implies that if/when cardbus bridges are > > converted to async suspend/resume, the driver should make sure that the > > lower-numbered devices wait for their sibling higher-numbered devices > > to suspend (and vice versa for resume). Awkward though it may be. > > Yes. However, this is an excellent case where the whole "the device layer > does things asynchronously" is really rather awkward. > > For cardbus, the nicest model really would be for the _driver_ to decide > to do some things asynchronously, after having done some other things > synchronously (to make sure of ordering). Have you considered the possibility of augmenting the design to allow this? Perhaps reserve a particular return code from the suspend routine to mean that asynchronous operations are still underway, so the PM core shouldn't automatically do the complete_all(). > So I suspect that we _can_ just do cardbus bridges asynchronously too, but > it really needs some care. I suspect to a first approximation we would > want to do the easy cases first, and ignore cardbus as being "known to > possibly have issues". Certainly. Start with the easy things and leave harder devices like cardbus bridges for later. > > > Subtle? Hell yes. > > > > I don't disagree. However the subtlety lies mainly in the matter of > > non-obvious dependencies. > > Yes. But we don't necessarily even _know_ those dependencies. Yep. Both non-obvious and non-known. > The Cardbus ones I know about, but really only because I wrote much of > that code initially when converting cardbus to look like the PCI bridge it > largely is. But how many other cases like that do we have that we have > perhaps never even hit, because we've never done anything out of order. > > > The ACPI relations are definitely something to worry about. It would > > be a good idea, at an early stage, to add those dependencies > > explicitly. I don't know enough about them to say more; perhaps Rafael > > does. > > Quite frankly, I would really not want to do ACPI first at all. Dear me, no! I wasn't saying ACPI should be made async; I was saying that ACPI "shadow" devices should be made to wait for their async PCI counterparts. > > Indeed. Perhaps you were too hasty in suggesting that PCI bridges > > should be async. > > Oh, yes. I would suggest that first we do _nothing_ async except for > within just a single USB tree, and perhaps some individual drivers like > the PS/2 keyboard controller (and do even that perhaps only for the PC > version, which we know is on the southbridge and not anywhere else). > > If that ends up meaning that we block due to PCI bridges, so be it. I > really would prefer baby steps over anything more complete. Agreed. I'm not in any hurry. Alan Stern _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
