On Wed, 22 May 2019, Bjorn Helgaas wrote: > On Wed, May 22, 2019 at 11:46:25PM +0800, Kai Heng Feng wrote: > > > On May 22, 2019, at 9:48 PM, Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote: > > > On Wed, May 22, 2019 at 11:42:14AM +0800, Kai Heng Feng wrote: > > >> at 6:23 AM, Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote: > > >>> On Wed, May 22, 2019 at 12:31:04AM +0800, Kai-Heng Feng wrote: > > >>>> There's an xHC device that doesn't wake when a USB device gets plugged > > >>>> to its USB port. The driver's own runtime suspend callback was called, > > >>>> PME signaling was enabled, but it stays at PCI D0. > > > > ... > > > And I guess this patch basically means we wouldn't call the driver's > > > suspend callback if we're merely going to stay at D0, so the driver > > > would have no idea anything happened. That might match > > > Documentation/power/pci.txt better, because it suggests that the > > > suspend callback is related to putting a device in a low-power state, > > > and D0 is not a low-power state. > > > > Yes, the patch is to let the device stay at D0 and don’t run driver’s own > > runtime suspend routine. > > > > I guess I’ll just proceed to send a V2 with updated commit message? > > Now that I understand what "runtime suspended to D0" means, help me > understand what's actually wrong. Kai's point is that the xhci-hcd driver thinks the device is now in runtime suspend, because the runtime_suspend method has been executed. But in fact the device is still in D0, and as a result, PME signalling may not work correctly. On the other hand, it wasn't clear from the patch description whether this actually causes a problem on real systems. The description only said that the problem was theoretical. > The PCI core apparently *does* enable PME when we "suspend to D0". > But somehow calling the xHCI runtime suspend callback makes the driver > unable to notice when the PME is signaled? According to Kai, PME signalling doesn't work in D0 -- or at least, it is _documented_ not to work in D0 -- even though it is enabled and the device claims to support it. In any case, I don't really see any point in "runtime suspending" a device while leaving it in D0. We might as well just leave it alone. Alan Stern
