linux-kernel - Re: RFC: Platform data for onboard USB assets

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Date:	Fri, 11 Mar 2011 11:45:20 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	andy.green@...aro.org
cc:	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Arnd Bergmann <arnd@...db.de>,
	Linux USB list <linux-usb@...r.kernel.org>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: RFC: Platform data for onboard USB assets

On Fri, 11 Mar 2011, Andy Green wrote:

> > Like I say, it's not just MAC addresses that can need configuring this
> > way - it can be other random "you're wired up this way" type
> > information that would normally be figured out from the USB IDs.
> 
> Yes that's exactly why I was thinking it's a class of requirement that 
> could reasonably be a little API and extending platform_data to it.  So 
> anyone with onboard USB device can take advantage if they need to, 
> because I guess we see gradually more boards like that.
> 
> The driver knows well all about the actual device, but there is a class 
> of configuration information that is defined by the physical board 
> itself - as you say "how it is wired" - and needs to be passed into the 
> driver to inform it of its "functional configuration".  When that 
> functional configuration information is a feature of the board alone, 
> actually the board definition file is the right place for it.

I don't see the point of doing this for USB devices, or hot-pluggable 
devices in general.

Suppose you bought another USB device that was just like the on-board
one, and plugged it into the system.  Why should the driver need to
treat the on-board device any different from the hot-plugged device?

Or to put it another way...  With external, hot-plugged USB devices,
there is no need to know "how it is wired".  The fact that it is on a 
USB bus is the only information necessary.  Why does anyone need to
know more than this for on-board USB devices?

Alan Stern

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