linux-kernel - Re: Non-enumerable devices on USB and other enumerable buses

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Message-ID: <20130814153906.GU6427@sirena.org.uk>
Date:	Wed, 14 Aug 2013 16:39:06 +0100
From:	Mark Brown <broonie@...nel.org>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Rob Herring <rob.herring@...xeda.com>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Stephen Warren <swarren@...dotorg.org>,
	Ian Campbell <ian.campbell@...rix.com>,
	Felipe Balbi <balbi@...com>,
	Grant Likely <grant.likely@...aro.org>,
	devicetree@...r.kernel.org, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: Non-enumerable devices on USB and other enumerable buses

On Wed, Aug 14, 2013 at 10:27:26AM -0400, Alan Stern wrote:
> On Wed, 14 Aug 2013, Mark Brown wrote:

> > I'd expect that we're just looking at hooks around connection and
> > disconnection here here - if we're looking at much more it seems like we
> > must be doing something wrong.

> Connection and disconnection of what?

The device on the bus.

> In the example mentioned earlier, the GPIOs to power an on-board USB
> hub would have to be initialized when the host controller was started.  
> You wouldn't want to wait for the on-board hub to be detected, because
> without those GPIOs set properly, it never would be discovered on the
> USB bus.  Right?

Yes, so you'd want callbacks when the device actually appears and
disappears.

> Perhaps the platform-level code would need to hook into the places
> where the discoverable bus is registered and unregistered.

We'd need some way to get information to the drivers still, and to
handle drivers that want to stop and start things.

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