Subject: Re: [PATCH] usb/fsl_qe_udc: Report disconnect before unbinding

From: Anton Vorontsov <[email-masked]>
Date: Wed, 12 Nov 2008 22:59:16 +0300

On Wed, Nov 12, 2008 at 02:38:02PM -0500, Alan Stern wrote:
> On Wed, 12 Nov 2008, Anton Vorontsov wrote:
> 
> > Gadgets disable endpoints in their disconnect callbacks, so
> > we must call disconnect before unbinding. This also fixes
> > muram memory leak, since we free muram in the qe_ep_disable().
> 
> > --- a/drivers/usb/gadget/fsl_qe_udc.c
> > +++ b/drivers/usb/gadget/fsl_qe_udc.c
> > @@ -2382,6 +2382,9 @@ int usb_gadget_unregister_driver(struct usb_gadget_driver *driver)
> >  		nuke(loop_ep, -ESHUTDOWN);
> >  	spin_unlock_irqrestore(&udc_controller->lock, flags);
> >  
> > +	/* report disconnect; the driver is already quiesced */
> > +	driver->disconnect(&udc_controller->gadget);
> > +
> >  	/* unbind gadget and unhook driver. */
> >  	driver->unbind(&udc_controller->gadget);
> >  	udc_controller->gadget.dev.driver = NULL;
> 
> Wouldn't it be better to do this before nuking the existing requests?  
> The comment is wrong; the gadget driver is _not_ quiesced at this
> point.  In fact the disconnect call is what quiesces the driver!

composite_unbind() says:

        /* composite_disconnect() must already have been called
         * by the underlying peripheral controller driver!
         * so there's no i/o concurrency that could affect the
         * state protected by cdev->lock.
         */

Which I read as "at disconnect time the controller should
already be disabled, no further i/o can happen". Which means
that we should nuke all pending requests and stop the
controller.

In this comment:
"/* report disconnect; the driver is already quiesced */"
"the driver" means "the udc driver", not the gadget driver.

FWIW, the PXA27x UDC controller also stops all activity and
completely disables the controller before calling the
disconnect().

> And wouldn't it be better to _skip_ doing this if the gadget wasn't 
> connected before?

Composite framework handles this. If there were no connections,
then the disconnect() is a nop (except the spin lock/unlock pair).

I'm not sure how the controller driver could tell if there
was a connection or not: it doesn't operate these terms.
What the udc controller knows is: how to report bus reset
and how to receive or transmit the data...

Thanks,

-- 
Anton Vorontsov
email: [email-masked]
irc://irc.freenode.net/bd2