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

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Message-ID: <4D7A4D52.6010501@linaro.org>
Date:	Fri, 11 Mar 2011 16:26:58 +0000
From:	Andy Green <andy@...mcat.com>
To:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
CC:	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 03/11/2011 04:03 PM, Somebody in the thread at some point said:
> On Fri, Mar 11, 2011 at 04:54:03PM +0100, Arnd Bergmann wrote:
>> On Friday 11 March 2011, Mark Brown wrote:
>
>>> It's arguable if this stuff is broken at all, from a hardware design
>>> point of view it's perfectly reasonable and if you're shipping volumes
>>> in the millions very small savings add up to interesting numbers easily.
>
>> It may be reasonable if you don't expect anyone to connect the
>> device to an ethernet port, but in that case you could save much
>> more by removing the ethernet chip and the socket along with the
>> eeprom.
>
>> Really, any machine without a fixed MAC address is a huge pain
>> for users, just google for "pandaboard mac address" to see
>> how much work this has caused people.
>
> I'm not familiar with the Pandaboard but most of the devices I've worked
> with that do this have unique MAC addresses but they store in other
> locations on the device (typically in flash).
>
> 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.

-Andy
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