linux-kernel - Re: [PATCH v3 3/3] usb: phy: hold wakeupsource when USB is enumerated in peripheral mode

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Date:	Mon, 13 Jul 2015 15:00:03 +0800
From:	Peter Chen <peter.chen@...escale.com>
To:	Sumit Semwal <sumit.semwal@...aro.org>
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

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.
 
> 
> If indeed we can't handle charger events in the way suggested by you,
> may I propose the following:
> 
> - implement this in USB-phy as proposed in Kiran's original patch,
> - keep it disabled by default, and add a module param to enable/disable it
> - for no vbus case, use another event (USB_EVENT_ENUMERATED /
> USB_EVENT_NONE? ) to identify connect / disconnect?
>      (OR, maybe don't do anything for such cases, since most likely
> the chipidea kind of implementations would handle it themselves?)
> 

In my opinion, we can do noop for wakeup source if it is a USB charger.

> Of course these are based on my limited reading of the USB code, so
> I'd be grateful if you'd let me know of any obvious gaps in my
> understanding!
> 
> > --
> >
> > Best Regards,
> > Peter Chen
> 
> 
> Best regards,
> Sumit.

-- 

Best Regards,
Peter Chen
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