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

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Message-ID: <20130716063117.GA30320@kroah.com>
Date:	Mon, 15 Jul 2013 23:31:17 -0700
From:	Greg KH <gregkh@...uxfoundation.org>
To:	Rong Wang <wr011235813@...il.com>
Cc:	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 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...

Felipe, any ideas?

greg k-h
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