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

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Message-ID: <F281D0F91ED19E4D8E63A7504E8A649803F5B0F8@039-SN2MPN1-021.039d.mgd.msft.net>
Date:	Sat, 20 Jul 2013 10:57:13 +0000
From:	Chen Peter-B29397 <B29397@...escale.com>
To:	Rong Wang <wr011235813@...il.com>
CC:	Greg KH <gregkh@...uxfoundation.org>,
	"balbi@...com" <balbi@...com>, Arnd Bergmann <arnd@...db.de>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Rong.Wang@....com" <Rong.Wang@....com>
Subject: RE: [PATCH] usb: udc: add gadget state kobject uevent


 
> 
> On Wed, Jul 17, 2013 at 10:36 AM, Peter Chen <peter.chen@...escale.com>
> wrote:
> > On Mon, Jul 15, 2013 at 11:31:17PM -0700, Greg KH wrote:
> >> On Tue, Jul 16, 2013 at 11:49:07AM +0800, Rong Wang wrote:
> >> > Hi Greg,
> >> >
> >> > The USB on our platform can change roles between HOST and GADGET,
> but
> >> > it is not capable of OTG.
> >>
> >> That kind of sounds like the definition of OTG :)
> >>
> >> > When the USB changes between roles the udev will run some scripts
> >> > automatically according to the udev rules.
> >>
> >> What exactly does udev/userspace see when the roles change?
> >>
> >> And what can trigger the change in roles?
> >>
> >> > The default role is GADGET, and we bind the g_mass_storage to the
> USB
> >> > GADGET role.
> >> >
> >> > We should secure the back end file storage between the device and
> the
> >> > host PC connecting to our device.
> >> > We need to know when the GADGET is really connect to a host PC, then
> >> > we can umount the file on the device
> >> > and export it to the g_mass_storage.
> >>
> >> I thought you already get an event for this, otherwise no one would be
> >> able to properly deal with this.
> >>
> >> > 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...
> >>
> >
> > If I understand correctly,  what Rong wants is udev can be notified the
> > udc state changes, like connect/disconnect event. Currently, we only
> > export it to /sys.
> 
> OK. Thanks for your share.
> 
> And you develop a new utility rather than udev to monitor that file?
> And you probably create a work queue in your udc driver to do this work?
> 
 
Not yet, no one complains it, so I haven't added it.
But, it is a useful user interface, Android has implemented similar functions
at its gadget driver.

Best regards,
Peter



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