On Sunday 24 January 2010, Alan Stern wrote: > On Sun, 24 Jan 2010, Rafael J. Wysocki wrote: > > > > There needs to be a public interface to this function available for > > > drivers that have non-tree constraints. The arguments should be the > > > device to wait for and the device doing the waiting (needed only to > > > determine whether the caller is running synchronously or not). > > > > Something like the patch below? > > Yes, exactly. Thanks. OK, I'll put it into the patchset after 5/8. > > > This will be necessary for USB. In fact, your current code (with patch > > > 7/8 applied) is subject to a race that will sometimes cause a > > > non-high-speed USB device to fail to resume from hibernation. > > > > That's the kind of information I need at this point. What exactly should be > > added to patch 7/8 to avoid this problem? > > I don't think there's anything you can do about it, really. It's an > obscure USB issue: If an EHCI controller was reset or loses power > during a system sleep (which always happens with hibernation and > sometimes happens with suspend-to-RAM, depending on the chipset and > firmware), then the EHCI controller must be resumed after all its > sibling companion OHCI/UHCI controllers, and USB devices below the > companion root hubs must be resumed after the EHCI root hub. > > With synchronous resume this happens automatically because the devices > in question are always registered in the appropriate order. But the > only way to meet these constraints with async resume is to add specific > code to the USB core to enforce the non-tree orderings. > > I intend to write this code, but merging it will be a little tricky. > You'll have to coordinate with Greg KH. OK, I don't think that's a big deal. I can defer patch 7/8 until that code has been merged. > If you have a non-high-speed USB device, you can test to see if this > problem is not just a figment of my imagination. To violate the first > constraint, add an ssleep(1) to the beginning of ohci_pci_resume() in > drivers/usb/host/ohci-pci.c or to the beginning of uhci_pci_resume() in > drivers/usb/host/uhci-hcd.c (depending on whether your companion > controllers are OHCI or UHCI). To violate the second constraint, add > an ssleep(1) to the beginning of ehci_bus_resume() in > drivers/usb/host/ehci-hub.c. Either constraint violation should cause > the device to be disconnected and then reconnected during an async > resume from hibernation, as opposed to simply being reset. I'll try that, but my mkinitrd automatically puts the USB drivers into initramfs. I guess I'll need to do some research to really verify it. :-) Rafael -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
