Hi Shawn, I noticed that the ChromeOS kernel tree is still using this particular patch, and thought it was probably time to revisit it. On Sat, May 25, 2013 at 09:57:57AM -0700, Shawn Nematbakhsh wrote: > Hi Sarah and Alan, > > Thanks for the comments. I will make the following revisions: > > 1. Call pm_runtime_get_noresume only when the first device is connected, > and call pm_runtime_put when the last device is disconnected. > 2. Wrap the calls in an ifdef CONFIG_USB_DEFAULT_PERSIST. > 3. Make sure that all pm_runtime_get_noresume calls have a corresponding > pm_runtime_put somewhere (originally the intent was to disable runtime > suspend "forever", but no longer). > > In principle, would the patch be acceptable with these revisions? The thread petered off with all other options turning out to be dead-ends, so yes, if you made those changes, you could get that patch upstream. I would like the ChromeOS kernel to be as close to upstream as possible, so please resubmit this patch with those changes. Thanks, Sarah Sharp > > On Sat, May 25, 2013 at 7:11 AM, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>wrote: > > > On Fri, 24 May 2013, Sarah Sharp wrote: > > > > > On Fri, May 24, 2013 at 11:12:57AM -0700, Shawn Nematbakhsh wrote: > > > > If a USB controller with XHCI_RESET_ON_RESUME goes to runtime suspend, > > > > a reset will be performed upon runtime resume. Any previously suspended > > > > devices attached to the controller will be re-enumerated at this time. > > > > This will cause problems, for example, if an open system call on the > > > > device triggered the resume (the open call will fail). > > > > > > That's ugly, but disabling runtime PM is going to have a big impact on > > > the power consumption of those systems. > > > > > > Alan, do you think this is really the right thing to be doing here? It > > > feels like userspace should just be able to deal with devices > > > disconnecting on resume. After all, there are lots of USB devices that > > > can't handle USB device suspend at all. > > > > This is a complicated issue. It depends on the runtime PM settings for > > both the device and the host controller. > > > > As just one aspect, consider the fact that if it wants to, userspace > > can already prevent the controller from going into runtime suspend. > > Always preventing this at the kernel level, even when no devices are > > plugged in, does seem too heavy-handed. > > > > > Shouldn't userspace just disable runtime PM for the USB device classes > > > that don't have a reset resume callback? > > > > That's not so easy, because the kernel changes over time. Userspace > > has no general way to tell which drivers have reset-resume support. > > > > > > Note that this change is only relevant when persist_enabled is not set > > > > for USB devices. > > > > > > Could we at least wrap the call in an ifdef CONFIG_USB_DEFAULT_PERSIST? > > > That way if people have USB persist turned off in their configuration, > > > their host will still be able to suspend. > > > > Not just that; the patch is incorrect on the face of it... > > > > > > @@ -4687,6 +4687,12 @@ int xhci_gen_setup(struct usb_hcd *hcd, > > xhci_get_quirks_t get_quirks) > > > > > > > > get_quirks(dev, xhci); > > > > > > > > + /* If we are resetting upon resume, we must disable runtime PM. > > > > + * Otherwise, an open() syscall to a device on our runtime > > suspended > > > > + * controller will trigger controller reset and device > > re-enumeration */ > > > > + if (xhci->quirks & XHCI_RESET_ON_RESUME) > > > > + pm_runtime_get_noresume(dev); > > > > + > > > > It adds a pm_runtime_get call with no corresponding pm_runtime_put. > > > > Alan Stern > > > > -- 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
