linux-kernel - Re: [PATCH v2 08/22] usb: chipidea: Remove locking in ci_udc

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Date:	Sat, 6 Aug 2016 15:54:35 +0800
From:	Peter Chen <hzpeterchen@...il.com>
To:	Stephen Boyd <stephen.boyd@...aro.org>
Cc:	linux-usb@...r.kernel.org, Felipe Balbi <balbi@...nel.org>,
	Arnd Bergmann <arnd@...db.de>,
	Neil Armstrong <narmstrong@...libre.com>,
	linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
	Bjorn Andersson <bjorn.andersson@...aro.org>,
	Peter Chen <peter.chen@....com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Andy Gross <andy.gross@...aro.org>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 08/22] usb: chipidea: Remove locking in ci_udc_start()

On Fri, Aug 05, 2016 at 02:53:56PM -0700, Stephen Boyd wrote:
> Quoting Peter Chen (2016-07-08 02:45:28)
> > On Thu, Jul 07, 2016 at 03:20:59PM -0700, Stephen Boyd wrote:
> > > We don't call hw_device_reset() with the ci->lock held, so it
> > > doesn't seem like this lock here is protecting anything. Let's
> > > just remove it. This allows us to call sleeping functions like
> > > phy_init() from within the CI_HDRC_CONTROLLER_RESET_EVENT hook.
> > > 
> > > Cc: Peter Chen <peter.chen@....com>
> > > Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > > Signed-off-by: Stephen Boyd <stephen.boyd@...aro.org>
> > > ---
> > >  drivers/usb/chipidea/udc.c | 3 ---
> > >  1 file changed, 3 deletions(-)
> > > 
> > > diff --git a/drivers/usb/chipidea/udc.c b/drivers/usb/chipidea/udc.c
> > > index 065f5d97aa67..f16be4710cdb 100644
> > > --- a/drivers/usb/chipidea/udc.c
> > > +++ b/drivers/usb/chipidea/udc.c
> > > @@ -1719,7 +1719,6 @@ static int ci_udc_start(struct usb_gadget *gadget,
> > >                        struct usb_gadget_driver *driver)
> > >  {
> > >       struct ci_hdrc *ci = container_of(gadget, struct ci_hdrc, gadget);
> > > -     unsigned long flags;
> > >       int retval = -ENOMEM;
> > >  
> > >       if (driver->disconnect == NULL)
> > > @@ -1746,7 +1745,6 @@ static int ci_udc_start(struct usb_gadget *gadget,
> > >  
> > >       pm_runtime_get_sync(&ci->gadget.dev);
> > >       if (ci->vbus_active) {
> > > -             spin_lock_irqsave(&ci->lock, flags);
> > >               hw_device_reset(ci);
> > >       } else {
> > >               usb_udc_vbus_handler(&ci->gadget, false);
> > > @@ -1755,7 +1753,6 @@ static int ci_udc_start(struct usb_gadget *gadget,
> > >       }
> > >  
> > >       retval = hw_device_state(ci, ci->ep0out->qh.dma);
> > > -     spin_unlock_irqrestore(&ci->lock, flags);
> > >       if (retval)
> > >               pm_runtime_put_sync(&ci->gadget.dev);
> > >  
> > 
> > The main purpose for this is disabling interrupt when reset controller,
> > in case the unexpected interrupts occur.
> > 
> > You can move this between hw_device_state.
> > 
> 
> Ok, but we don't hold the ci->lock in ci_udc_vbus_session(). Is that a
> bug as well?

I agree with your patch. In fact, during the reset controller, the
interrupt has not been enabled, it should no unexpected interrupt.

-- 

Best Regards,
Peter Chen