On Thursday, 26 of June 2008, Alan Stern wrote: > On Thu, 26 Jun 2008, Rafael J. Wysocki wrote: > > > > Question: Does the PME Status ever get cleared at any other times? > > > > Currently, PME# status is only cleared when executing pci_pme_active() (for > > example via pci_enable_wake()). > > > > > For instance, suppose a PCI device does use PME# to wake up the system. > > > Does its status get cleared? > > > > If the driver of the device executes pci_enable_wake(dev, PCI_D0, false) during > > resume, then the PME# status will be cleared. > > Hmm. So if the resume routine doesn't get called for some reason then > most likely the status won't get cleared. That's correct. > > Do you think the core should clear PME# status automatically in that case? > > Yes. Okay, but that will require us to add the clearing of PME# to the PCI resume/restore callbacks. Perfectly doable, but I'd prefer to do that on top of the $subject patch. > > > Or suppose a PCI device is runtime-suspended and it generates a wakeup > > > request? This will turn on PME# at a time when the system isn't asleep > > > -- what happens then? Does it get lost somewhere in the bowels of > > > ACPI? > > > > Currently, yes, AFAICS. > > Back around last November some initial patches were posted by Shaohua > Li, as part of Bugzilla #6892. OK, I will. > You'd probably be interested to read through the entire bug report. Maybe we > should start working on it again. I have nothing against that, but quite frankly I wouldn't like it to become a road block for the present patch series. Thus, I'd like to add new patches on top of it rather than to modify it to achieve new goals. > > > Does the PCI core need new code to handle such things? > > > > Well, I thought of adding such things like the clearing of PME# status to the > > PCI bus type suspend/resume callbacks. > > > > Apart from this, I think that to implement PCI runtime PM we'll need to add > > some new code. First of all, we need to handle the case when some devices are > > in low power states before suspend/hibernation. Second, we need to handle PME# > > generated by devices being in low power states (or even in D0) at run time and > > that will certainly require new code. > > Yes it will. We don't have any runtime PM infrastructure for PCI yet. > > Although to tell the truth, I'm not sure how important it is. How much > power can we save by doing runtime suspends of PCI devices? With USB > controllers, for example, much or most of the savings comes from > disabling the USB portions of the device, which we _are_ doing. It's > not clear how much more would be gained by shutting down the PCI > portions as well. That can only be determined by experimentation, IMO, so in fact we'll need a prototype implementation to find that out. Thanks, Rafael -- 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
