[PATCH v2 08/22] usb: chipidea: Remove locking in ci_udc_start()

[Stephen Boyd]

Quoting Peter Chen (2016-08-06 00:54:35)
> 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 at nxp.com>
> > > > Cc: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
> > > > Signed-off-by: Stephen Boyd <stephen.boyd at linaro.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.
> 

So then we can leave this patch as is? It still isn't clear to me what
sequence of events that would cause a problem if we don't hold the
ci->lock around hw_device_state().