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

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Date:	Fri, 16 Aug 2013 19:39:34 +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 Fri, Aug 16, 2013 at 10:42:10AM -0400, Alan Stern wrote:

> Okay, let's see if I understand your problem.  You've got a driver that
...
> Is that it?

Yes, I think that's it.

> The difficulty with the first proposal is that subsystems aren't
> designed to allow that sort of thing.  They expect to be able to
> communicate with the devices they manage, during enumeration and
> probing at least.  The difficulty with the second proposal is that it
> requires duplicating the power-on code.

> My feeling is that the second answer involves less work and less
> complexity than the first.  Both proposals require additional
> "run-once" code (to do the partial instantiations or the initial
> power-ons), but the first proposal also requires the subsystem's 
> detection and enumeration routines to be adjusted so that they can work 
> even when the device is incommunicado.

Right, but like I say I'm not sure that the modifications required are
substantially different to those for handling a device powering up and
down on the bus or those for getting platform data to a device when it
does enumerate.  I'd also not be so sure about the run once code, that
is only the case for devices that can't completely idle themselves at
runtime.

> (The second proposal also has the advantage that the power-on code may 
> be shared between the driver and the subsystem.)

Can you explain in more detail please, I don't follow?

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