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

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Message-ID: <20130812203803.GF6427@sirena.org.uk>
Date:	Mon, 12 Aug 2013 21:38:03 +0100
From:	Mark Brown <broonie@...nel.org>
To:	Stephen Warren <swarren@...dotorg.org>
Cc:	Mark Rutland <mark.rutland@....com>,
	Olof Johansson <olof@...om.net>,
	Alan Stern <stern@...land.harvard.edu>,
	"rob.herring@...xeda.com" <rob.herring@...xeda.com>,
	Pawel Moll <Pawel.Moll@....com>,
	Ian Campbell <ian.campbell@...rix.com>,
	Felipe Balbi <balbi@...com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	"devicetree@...nel.org" <devicetree@...r.kernel.org>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Non-enumerable devices on USB and other enumerable buses

On Mon, Aug 12, 2013 at 12:08:17PM -0600, Stephen Warren wrote:

> In a similar way, I wonder if the USB case can be considered the same
> way? This seems less like a good fit since I don't expect the resources
> are always so similar there, and also there's the case of the bus being
> potentially behind a few levels of USB hub.

That won't work for the hub on Arndale in a system where it's fully
wired up - it's got an I2C interface for control and the idea is that
you bring it out of reset, write the configuration out via I2C and then
you can complete startup using a GPIO or another I2C command.

> And of course it all gets a little more messy when you get
> board-specific logic that needs setup, rather than something more common
> across multiple devices.

I think we could probably cover many cases by putting common things onto
the bus but we still need to confront the cases where the device driver
really does need to get involved in what's going on.  Things like the
SDIO WiFi cards seem very interchangable as you say and would probably
benefit a lot but there's other applications that are less regular.

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