Date: Mon, 20 Jul 2015 15:15:56 +0800
From: Peter Chen <peter.chen@freescale.com>
To: Sumit Semwal <sumit.semwal@linaro.org>
CC: Felipe Balbi <balbi@ti.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "linux-usb@vger.kernel.org" <linux-usb@vger.kernel.org>,
        Android Kernel Team <kernel-team@android.com>,
        Arve =?iso-8859-1?B?SGr4bm5lduVn?= <arve@android.com>,
        Benoit Goby <benoit@android.com>, Todd Poynor <toddpoynor@google.com>
Subject: Re: [PATCH v3 3/3] usb: phy: hold wakeupsource when USB is
 enumerated in peripheral mode
Message-ID: <20150720071555.GA5715@shlinux2>
References: <20141125144544.GC6360@saruman>
 <CA+RfmHZRqMwiSAZ7kpn+0_8a+25O+hRKxGJuK6im6fX0dzB8Nw@mail.gmail.com>
 <CA+RfmHb9OQ1Y_c-93jgpWWfNpTNLE84+Z70bOMtNrbJhQSWQAA@mail.gmail.com>
 <20150113161802.GD16533@saruman>
 <20150114012653.GB14944@shlinux2>
 <CAO_48GH=85GjXQu+b56RfnC5gTTVqNeo=Q7FsY5TvazvBAST_Q@mail.gmail.com>
 <20150608083152.GB6743@shlinux2>
 <CAO_48GE1rvvFBqCAkHzRTfVqSVSbUqqO2w2pbg3+byJtchgDVw@mail.gmail.com>
 <20150713070002.GA12197@shlinux2>
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On Mon, Jul 20, 2015 at 01:18:35PM +0530, Sumit Semwal wrote:
> On 13 July 2015 at 12:30, Peter Chen <peter.chen@freescale.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@freescale.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@freescale.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@linaro.org> wrote:
> >> >> >> > > Hi Felipe,
> >> >> >> > >
> >> >> >> > > On 25 November 2014 at 20:15, Felipe Balbi <balbi@ti.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.
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
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