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

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Message-Id: <201103141554.28515.arnd@arndb.de>
Date:	Mon, 14 Mar 2011 15:54:28 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Grant Likely <grant.likely@...retlab.ca>
Cc:	andy.green@...aro.org, Andy Green <andy@...mcat.com>,
	Linux USB list <linux-usb@...r.kernel.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	"Greg Kroah-Hartman" <gregkh@...e.de>
Subject: Re: RFC: Platform data for onboard USB assets

On Friday 11 March 2011, Grant Likely wrote:
> On Fri, Mar 11, 2011 at 2:50 AM, Andy Green <andy@...mcat.com> wrote:
> > Hi -
> >
> > platform_data is a well established way in Linux to pass configuration data
> > up to on-board assets from a machine file like mach-xyz.c.  It's also
> > supported to pass platform_data up to devices that are probed asynchronously
> > from busses like i2c as well, which is very handy.
> >
> > However AFAIK it's not possible to bind platform_data to probed USB devices
> > as it stands.
> 
> Oh, please no.
> 
> platform_data is an ugly non-type-checked anonymous pointer.  If you
> need to pass data to a driver, use something better designed.  A
> device tree fragment would work, or provide some kind of query api.
> platform_data is definitely the wrong approach.

I'd still hope that we could do without either for hotpluggable
devices, but a device tree object fits better here, because
we already have ways to associate the data in the device node
with any device, not just platform devices, and the key/value
pairs make it much more flexible than platform data.

	Arnd
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