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Message-ID: <CALAqxLWf0_73spYd68-bnYZp5evLNjcFwBqevVdHCoziG9paBA@mail.gmail.com> Date: Thu, 11 Apr 2019 20:59:17 -0700 From: John Stultz <john.stultz@...aro.org> To: Yu Chen <chenyu56@...wei.com> Cc: Linux USB List <linux-usb@...r.kernel.org>, "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" <devicetree@...r.kernel.org>, lkml <linux-kernel@...r.kernel.org>, Zhuangluan Su <suzhuangluan@...ilicon.com>, Kongfei <kongfei@...ilicon.com>, "Liuyu (R)" <liuyu712@...ilicon.com>, wanghu17@...ilicon.com, butao <butao@...ilicon.com>, chenyao11@...wei.com, fangshengzhou@...ilicon.com, Li Pengcheng <lipengcheng8@...wei.com>, songxiaowei@...ilicon.com, YiPing Xu <xuyiping@...ilicon.com>, xuyoujun4@...wei.com, Yudongbin <yudongbin@...ilicon.com>, Zang Leigang <zangleigang@...ilicon.com>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Heikki Krogerus <heikki.krogerus@...ux.intel.com>, Hans de Goede <hdegoede@...hat.com>, Andy Shevchenko <andy.shevchenko@...il.com> Subject: Re: [PATCH v5 09/13] usb: roles: Add usb role switch notifier. On Thu, Apr 11, 2019 at 6:12 PM John Stultz <john.stultz@...aro.org> wrote: > > On Thu, Mar 28, 2019 at 9:14 PM Yu Chen <chenyu56@...wei.com> wrote: > > > > This patch adds notifier for drivers want to be informed of the usb role > > switch. > > > > Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org> > > Cc: Heikki Krogerus <heikki.krogerus@...ux.intel.com> > > Cc: Hans de Goede <hdegoede@...hat.com> > > Cc: Andy Shevchenko <andy.shevchenko@...il.com> > > Cc: John Stultz <john.stultz@...aro.org> > > Suggested-by: Heikki Krogerus <heikki.krogerus@...ux.intel.com> > > Signed-off-by: Yu Chen <chenyu56@...wei.com> > > Hey Yu Chen! > Thanks again for sending this patch out! As mentioned in my > comments with the other patches, I've got one proposal I wanted to > share to try to avoid state initialization races that I've seen with > this patchset. > > > diff --git a/drivers/usb/roles/class.c b/drivers/usb/roles/class.c > > index f45d8df5cfb8..e2caaa665d6e 100644 > > --- a/drivers/usb/roles/class.c > > +++ b/drivers/usb/roles/class.c > > @@ -58,6 +61,20 @@ int usb_role_switch_set_role(struct usb_role_switch *sw, enum usb_role role) > > } > > EXPORT_SYMBOL_GPL(usb_role_switch_set_role); > > > > +int usb_role_switch_register_notifier(struct usb_role_switch *sw, > > + struct notifier_block *nb) > > +{ > > + return blocking_notifier_chain_register(&sw->nh, nb); > > +} > > +EXPORT_SYMBOL_GPL(usb_role_switch_register_notifier); > > As noted earlier, one issue I've seen is that the hisi_hikey_usb > driver's notifier may not get called early enough to receive > notification of the initial usb state. > > It seems like on registration here, we should take the lock, read the > role state and immediately call the notifier to properly initialize > it? I suspect that should close the window for any state races around > driver probe timings and > > Does that make sense? I have roughly prototyped this but need to do > additional testing. So these seem to be working ok. First, the notifier call on register change: https://git.linaro.org/people/john.stultz/android-dev.git/commit/?h=dev/hikey960-mainline-WIP&id=1d312db9763c2449c3cf5b3383b1f33390f8ce7b Second, the current_dr_role change for dwc3: https://git.linaro.org/people/john.stultz/android-dev.git/commit/?h=dev/hikey960-mainline-WIP&id=b80b536de76eb80f7df0846aa54ac22e2b4ffe4e Feel free to fold/rework those changes into your patch set. thanks -john
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