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

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Message-ID: <20130717023649.GD29679@nchen-desktop>
Date:	Wed, 17 Jul 2013 10:36:50 +0800
From:	Peter Chen <peter.chen@...escale.com>
To:	Greg KH <gregkh@...uxfoundation.org>
CC:	Rong Wang <wr011235813@...il.com>, <balbi@...com>,
	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 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.

-- 

Best Regards,
Peter Chen

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