On Thu, Aug 11, 2016 at 04:07:21PM +0800, Baolin Wang wrote: > Hi Peter, > > On 11 August 2016 at 14:54, Peter Chen <hzpeterchen@xxxxxxxxx> wrote: > > On Thu, Aug 11, 2016 at 11:08:52AM +0800, Baolin Wang wrote: > >> Hi Alan, > >> > >> On 10 August 2016 at 22:25, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > >> > On Wed, 10 Aug 2016, Baolin Wang wrote: > >> > > >> >> >> >> For example: No slave attached----> usb interface runtime suspend > >> >> >> >> ----> usb device runtime suspend -----> xhci suspend -----> power off > >> >> >> >> usb controller. After that if the system wants to enter suspend state, > >> >> >> >> then it also will issue usb_dev_suspend(), then the > >> >> >> >> pm_runtime_resume() function (issued in choose_wakeup() function) will > >> >> >> >> return -ESHUTDOWN due to xhci has been suspend and hardware is not > >> >> >> >> accessible. > >> >> >> > > >> >> >> > Why the controller does not be resumed when the root hub has issued > >> >> >> > runtime resume? > >> >> >> > >> >> >> Because now there is no slave attached, we will not power on usb > >> >> >> controller and resume xhci. > >> >> >> > >> >> > > >> >> > I don't know why you set policy like this. Even the controller is > >> >> > resumed, it will still be suspended by system suspend. What's more, > >> >> > if you disallow it, how can you change your wakeup setting? > >> >> > Eg, at runtime suspend, we enable wakeup by default. But for system > >> >> > sleep, we disable wakeup by default. > >> >> > > >> >> > At runtime, if there is no device on the port, even we resumes the > >> >> > controller and roohub, it still will be suspended soon. > >> >> > >> >> For saving power, if there is no slave attached, why we need to power > >> >> on usb controller and resume xhci? Especially for mobile device. > >> > > >> > You need to power-on the USB controller in order to change the wakeup > >> > setting. > >> > >> pm_runtime_resume() function issued in choose_wakeup() can just resume > >> usb device, which can not power-on the USB controller and resume xHCI. > >> Cause the user won't know you need to power-on usb controller now, > >> then how to power-on the USB controller when changing wakeup setting? > >> > >> > > >> >> Moreover the usb device runtime suspend/resume is separate with xhci > >> >> suspend/resume, when xhci entered suspend state, only slave attaching > >> >> can resume xhci. > >> > > >> > That's right. Suppose the user wants the system to stay asleep when a > >> > slave attaches. But when you suspended the xHCI controller, it was set > >> > to wake up when a new slave attaches. So when a slave is attached, the > >> > controller will wake up the system. That's bad. > >> > > >> > If the wakeup setting needs to be changed when the system suspend > >> > begins, then you have to power-on the controller to make that change. > >> > > >> > Given a choice between using a little power or behaving incorrectly, > >> > you should choose to use the power. > >> > >> OK. But that is a real problem. It will pm_runtime_resume() falied > >> (issued in choose_wakeup()), cause usb controller has powered-off and > >> xHCI controller has suspended and we have no method to notify the user > >> to power-on USB controller. Any good suggestion to solve this, Alan > >> and Peter? Thanks. > >> > > > > Maybe you can show us the call stack why pm_runtime_resume has failed > > at your environment. > > OK. I try to explain it at below: > > For example: No slave attached----> usb interface runtime suspend > ----> usb device runtime suspend (routine is: > usb_suspend_device()--->generic_suspend() --> hcd_bus_suspend()--> > xhci_bus_suspend()) -----> xhci_ suspend() -----> power off usb > controller. After that if the system wants to enter suspend state, > then it also will issue usb_dev_suspend(), then the > pm_runtime_resume() function (issued in choose_wakeup() function) will > return -ESHUTDOWN due to xhci has been suspend and hardware is not accessible. > > We issue the pm_runtime_resume() function routine: usb_resume_device() > ----> generic_resume() ----> hcd_bus_resume() ---> xhci_bus_resume(), > but now xHCI is not accessible due to xhci_suspend() is issued and USB > controller is power off when no slave attached. That is why > pm_runtime_resume failed. > What host controller driver you are using? Assume you are using xhci-plat.c. The problem for you is this driver does not implement runtime pm operations, so the flag HCD_FLAG_HW_ACCESSIBLE is not set. Maybe Robert's patch is a good start for you [1] [1] http://www.spinics.net/lists/linux-usb/msg144602.html -- Best Regards, Peter Chen -- 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
