Date:	Mon, 20 Jul 2015 18:37:57 +0530
From:	Sumit Semwal <sumit.semwal@...aro.org>
To:	Peter Chen <peter.chen@...escale.com>
Cc:	Felipe Balbi <balbi@...com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	Android Kernel Team <kernel-team@...roid.com>,
	Arve Hjønnevåg <arve@...roid.com>,
	Benoit Goby <benoit@...roid.com>,
	Todd Poynor <toddpoynor@...gle.com>
Subject: Re: [PATCH v3 3/3] usb: phy: hold wakeupsource when USB is enumerated
 in peripheral mode

Hi Peter,

On 20 July 2015 at 12:45, Peter Chen <peter.chen@...escale.com> wrote:
> On Mon, Jul 20, 2015 at 01:18:35PM +0530, Sumit Semwal wrote:
>> On 13 July 2015 at 12:30, Peter Chen <peter.chen@...escale.com> wrote:
>> > On Mon, Jul 13, 2015 at 01:26:23PM +0530, Sumit Semwal wrote:
>> >> Hi Peter,
>> >>
>> >> On 8 June 2015 at 14:02, Peter Chen <peter.chen@...escale.com> wrote:
>> >> > On Mon, Jun 08, 2015 at 12:37:00PM +0530, Sumit Semwal wrote:
>> >> >> H Peter, Felipe,
>> >> >>
>> >> >> On 14 January 2015 at 06:56, Peter Chen <peter.chen@...escale.com> wrote:
>> >> >> > On Tue, Jan 13, 2015 at 10:18:02AM -0600, Felipe Balbi wrote:
>> >> >> >> On Tue, Jan 13, 2015 at 04:02:20PM +0530, Kiran Raparthy wrote:
>> >> >> >> > Hi Felipe,
>> >> >> >> >
>> >> >> >> > On 1 December 2014 at 11:09, Kiran Raparthy <kiran.kumar@...aro.org> wrote:
>> >> >> >> > > Hi Felipe,
>> >> >> >> > >
>> >> >> >> > > On 25 November 2014 at 20:15, Felipe Balbi <balbi@...com> wrote:
>> >> >> >> > >> On Tue, Nov 25, 2014 at 07:06:18AM +0000, Peter Chen wrote:
>> >> >> >> > >>>
>> >> >> >> > >>> >
>> >> >> >> > >>> > usb: phy: hold wakeupsource when USB is enumerated in peripheral mode
>> >> >> >> > >>> >
>> >> >> >> > >>> > Some systems require a mechanism to prevent system to enter into suspend
>> >> >> >> > >>> > state when USB is connected and enumerated in peripheral mode.
>> >> >> >> > >>> >
>> >> >> >> > >>> > This patch provides an interface to hold a wakeupsource to prevent suspend.
>> >> >> >> > >>> > PHY drivers can use this interface when USB is connected and enumerated in
>> >> >> >> > >>> > peripheral mode.
>> >> >> >> > >>> >
>> >> >> >> > >>> > A timed wakeupsource is temporarily held on USB disconnect events, to allow
>> >> >> >> > >>> > the rest of the system to react to the USB disconnection (dropping host
>> >> >> >> > >>> > sessions, updating charger status, etc.) prior to re-allowing suspend.
>> >> >> >> > >>> >
>> >> >> >> > >>>
>> >> <snip>
>> >> >>
>> >> >> Kiran is unable to continue on this patch anymore, so despite my very
>> >> >> limited usb experience, I would like to take this over and with your
>> >> >> help, take it to closure.
>> >> >>
>> >> >> From what I understand, it might be possible to do this either at the
>> >> >> usb controller driver (where it detects if it has enumerated in host
>> >> >> mode or device mode) or in the extcon driver (where it detects VBUS
>> >> >> etc..) -  which would be a cleaner / more logical way to do it?
>> >> >>
>> >> >> Thanks for all your help!
>> >> >
>> >> > I added my suggestions below:
>> >> >
>> >> > My opinion is: if we need this feature, we should depend on gadget's
>> >> > state, eg 'configured', not vbus level. The system suspend should be
>> >> > allowed if the gadget state is 'suspended' even vbus is still there.
>> >> >
>> >> > And when the gadget goes to suspend or reset or disconnect state, we can
>> >> > go to disable this wakeup source.
>> >> >
>> >> > At drivers/usb/gadget/composite.c, we can know the gadget's state.
>> >> >
>> >> Thanks very much for your suggestion, and apologies in the delay in response.
>> >>
>> >> I tried to study your suggestion and the code a little bit more, and
>> >> while I liked your idea quite a bit, I also realised that for the case
>> >> of letting the USB charger use cases, in gadget framework, there
>> >> doesn't seem to be a way to get the USB_EVENT_CHARGER, since charger
>> >> would likely not be a gadget.
>> >>
>> >> In this case, how'd we be able to enable / disable wakeup_source for
>> >> charger events?
>> >
>> > We may not prevent the system entering system if it is a charger, isn't
>> > it, so don't need to consider USB charger.
>> >
>> Thanks for your comments, Peter!
>> From the Android code that I see, it seems that for a charger
>> connect/disconnect, some systems might require some time to react to
>> the change in power, and hence there's a timed-out wakeup event for
>> USB charger cases. That;s where the consideration for USB chargers
>> came from.
>
> Current udc core has an API usb_gadget_set_state set its state
> according to usb ch9. For this wakeup source case, if the peripheral
> has been configured, it can hold wakeup source. Otherise, just have
> a timeout wake lock.
Thank you for your kind hint. Let me toy with this change and update.

> Below are some reference code:
>
> diff --git a/drivers/usb/gadget/udc/udc-core.c
> b/drivers/usb/gadget/udc/udc-core.c
> index d69c355..018f534 100644
> --- a/drivers/usb/gadget/udc/udc-core.c
> +++ b/drivers/usb/gadget/udc/udc-core.c
>
> @@ -136,6 +138,16 @@ static void usb_gadget_state_work(struct
>                 work_struct *work)
>
>         if (udc) {
>                 sysfs_notify(&udc->dev.kobj, NULL, "state");
>                        switch (gadget->state) {
>                         case    USB_STATE_CONFIGURED:
>                         __pm_stay_awake(&x->wsource);
>                                 break;
>                         default:
>                         __pm_wakeup_event(&x->wsource,
>                                         USB_DEFAULT_WAKEUP_SRC_TIMEOUT);
>                         break;
>                   }
>         }
>
>
> --
>
> Best Regards,
> Peter Chen

Best regards,
Sumit.
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