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

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Message-ID: <Pine.LNX.4.44L0.1308141209410.1701-100000@iolanthe.rowland.org>
Date:	Wed, 14 Aug 2013 12:14:06 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Mark Brown <broonie@...nel.org>
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, 14 Aug 2013, Mark Brown wrote:

> 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.

No, no -- this is exactly the point I was trying to make.  The on-board
hub _won't_ appear on the USB bus until the GPIOs are set.  Therefore
the callback to set the GPIOs needs to be at a different place, not
when the device appears.

> > 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.

Um...  What exactly does this mean?  It's so generic, it could apply to
anything under drivers/.  After all, what driver doesn't want to stop
and start things?

Alan Stern

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