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

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Message-ID: <20110311170807.GV1760@opensource.wolfsonmicro.com>
Date:	Fri, 11 Mar 2011 17:08:07 +0000
From:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
To:	Greg KH <greg@...ah.com>
Cc:	Arnd Bergmann <arnd@...db.de>, andy.green@...aro.org,
	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, Mar 11, 2011 at 08:56:42AM -0800, Greg KH wrote:
> On Fri, Mar 11, 2011 at 04:48:50PM +0000, Mark Brown wrote:

> > USB itself is discoverable but the when the USB bus you're looking at is
> > one that's soldered down onto a board in a specific design all bets are
> > off regarding how complete the information you get will be.  On a basic
> > level the designers may have done things like omit the configuration
> > EEPROMs that would set the device IDs that the driver should be relying
> > on to identify the hardware configuration.  There may be other, nastier,
> > things going on.

> Then you use the existing platform data for your USB host controller
> driver.  Doesn't that work today just fine?

Wrong end of the bus.  This stuff is simple enough to deal with in a
system specific fashion, the standard solution would be to patch the
relevant drivers to hard code whatever is required.

> > You really can't make this assumption about discoverable buses on
> > embedded devices.  The discoverability will get you most of the way
> > there but not always all of the way there.

> Then the bus is not really USB, sorry.  USB is discoverable, _and_ can
> support enumeration in non-deterministic ways.  If people are using it
> in other ways then it is not USB and is something else.

That's certainly a valid way of looking at things but it doesn't really
move mainline support for systems which do stuff like this forward.

On the bright side I don't generally have to work on this stuff myself :)
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