Date: Fri, 11 Mar 2011 08:56:42 -0800
From: Greg KH <greg@kroah.com>
To: Mark Brown <broonie@opensource.wolfsonmicro.com>
Cc: Arnd Bergmann <arnd@arndb.de>, andy.green@linaro.org,
        Linux USB list <linux-usb@vger.kernel.org>,
        lkml <linux-kernel@vger.kernel.org>
Subject: Re: RFC: Platform data for onboard USB assets
Message-ID: <20110311165642.GA9996@kroah.com>
References: <4D79F068.2080009@linaro.org>
 <201103111331.13932.arnd@arndb.de>
 <20110311152938.GB29920@sirena.org.uk>
 <201103111654.04089.arnd@arndb.de>
 <20110311160308.GQ1760@opensource.wolfsonmicro.com>
 <20110311161421.GA7843@kroah.com>
 <20110311162759.GS1760@opensource.wolfsonmicro.com>
 <20110311163522.GA9291@kroah.com>
 <20110311164850.GT1760@opensource.wolfsonmicro.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20110311164850.GT1760@opensource.wolfsonmicro.com>
User-Agent: Mutt/1.5.21 (2010-09-15)
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 2263
Lines: 47

On Fri, Mar 11, 2011 at 04:48:50PM +0000, Mark Brown wrote:
> On Fri, Mar 11, 2011 at 08:35:22AM -0800, Greg KH wrote:
> > On Fri, Mar 11, 2011 at 04:27:59PM +0000, Mark Brown wrote:
> 
> > > I'm actually not that fussed about the MAC address use case itself and
> > > do tend to agree with you that that's handlable in userspace but for the
> > > other things that might need to be configured there's a lot of things
> > > that for non-discoverable buses we're currently passing through platform
> > > data so switching to bouncing things through userspace would itself be a
> > > substantial change from other systems.
> 
> > But USB _is_ discoverable, that's my point.
> 
> 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?

> > > You can't in general rely on the system being neatly abstracted and
> > > while discoverable buses do avoid many problems in this sort of area
> > > there are still things which can only be discovered through reference to
> > > the schematics or similar, especially if you care about the microamps.
> 
> > Again, that's not USB, so it isn't relevant here.
> 
> 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.

thanks,

greg k-h
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/