linux-kernel - Re: [PATCH] usb: udc: add gadget state kobject uevent

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Date:	Wed, 17 Jul 2013 11:37:35 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Felipe Balbi <balbi@...com>
cc:	Rong Wang <wr011235813@...il.com>,
	Greg KH <gregkh@...uxfoundation.org>,
	Arnd Bergmann <arnd@...db.de>, <linux-usb@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <Rong.Wang@....com>
Subject: Re: [PATCH] usb: udc: add gadget state kobject uevent

On Wed, 17 Jul 2013, Felipe Balbi wrote:

> On Wed, Jul 17, 2013 at 09:04:54PM +0800, Rong Wang wrote:
> > Hi Felipe,
> > 
> > On Wed, Jul 17, 2013 at 3:57 PM, Felipe Balbi <balbi@...com> wrote:
> > > Hi,
> > >
> > > On Mon, Jul 15, 2013 at 11:31:17PM -0700, Greg KH wrote:
> > >> > The question is since we default GADGET, so the g_mass_storage.ko is
> > >> > installed early but connecting to a host PC
> > >> > is randomly, But the udev has no idea when a host PC connects our device.
> > >> >
> > >> > So we consider it's reasonable to let the udev know the GADGET device state.
> > >> > Is there any alternative to our question?
> > >>
> > >> I thought we already export events for gadget device states, have you
> > >> looked for them?  I can't dig through the code at the moment, but this
> > >> seems like a pretty common issue...
> > >>
> > >> Felipe, any ideas?
> > >
> > > we already expose that in sysfs. IIRC udev can act on sysfs changes,
> > > no ?
> > 
> > I do not know if udev can polling sysfs file content change. I'll study this.
> > 
> > But the change is triggered by calling usb_gadget_set_state, and I find
> > composite framework do not call this. Then we should do this common work
> > in every udc driver?
> 
> yes. Only the UDC driver knows when the controller is moving among those
> states.

Not quite.  Only the gadget driver knows when the transition between 
ADDRESS and CONFIGURED occurs.  This should be added to composite.c.

Alan Stern

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