On Fri, 21 Nov 2014, Benson Leung wrote: > Sorry for the delay in my response. I did some more checking of my > particular failure, and my commit message is incorrect. The > usb_kill_urb is actually not the cause of this problem. It does not > result in autosuspend_check() itself, and is only serving to add some > delay. > > hidraw_release() in hidraw.c calls drop_ref(), which calls the > following in sequence upon clearing the last reader : > /* close device for last reader */ > hid_hw_power(hidraw->hid, PM_HINT_NORMAL); > hid_hw_close(hidraw->hid); > > hid_hw_power results in a usb_autopm_put_interface. In this case, the > reference count is decremented to 0, and a delayed autosuspend request > is attempted. > hid_hw_close leads to usbhid_close, which clears needs_remote_wakeup. > > However, there's no guarantee that the clear of needs_remote_wakeup > will occur before the delayed work ( runtime_idle() -> > autosuspend_check() ) runs. Moving usbhid->intf->needs_remote_wakeup > = 0 to before the usb_kill_urb(usbhid->urbin) only serves to reduce > the amount of time between these events and makes this particular > failure less likely. > > The correct solution is to put get/put around each change of > needs_remote_wakeup, as that will correctly trigger another delayed > autosuspend_check(), whose result is affected by the state of > needs_remote_wakeup. > > Since autosuspend_check() occurs as delayed work, I think it is > appropriate to add get/put around the clear in usbhid_stop as well. As Oliver pointed out, there's no real need to resume a device which is already suspended (the only effect would be to allow it to suspend again but with wakeup disabled -- and this would happen anyway if a wakeup occurred). Instead of using get and put, we should have an idle call. There is no USB wrapper for pm_runtime_idle calls, but one could be added. Still, in the meantime can you check to see what happens if you add pm_runtime_idle(&usbhid->intf->dev); in usbhid_close() just after needs_remote_wakeup is set to 0? You can do the same thing in usbhid_stop() if you want. 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
