linux-kernel - Re: MTD EEPROM support and driver integration

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Date:	Thu, 11 Jul 2013 19:05:06 +0200
From:	Maxime Ripard <maxime.ripard@...e-electrons.com>
To:	Mark Brown <broonie@...nel.org>
Cc:	Arnd Bergmann <arnd@...db.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	David Woodhouse <dwmw2@...radead.org>,
	Artem Bityutskiy <dedekind1@...il.com>,
	Shawn Guo <shawn.guo@...aro.org>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	oliver@...inagl.nl, linux-mtd@...ts.infradead.org,
	Wolfram Sang <wsa@...-dreams.de>,
	Jean Delvare <khali@...ux-fr.org>, linux-i2c@...r.kernel.org
Subject: Re: MTD EEPROM support and driver integration

Hi Mark,

On Tue, Jul 09, 2013 at 03:55:10PM +0100, Mark Brown wrote:
> On Mon, Jul 08, 2013 at 10:25:38PM +0200, Maxime Ripard wrote:
> > On Mon, Jul 08, 2013 at 09:34:26AM +0100, Mark Brown wrote:
> 
> > > I'd really like to see more discussion of this "DT parsing code for
> > > regmap" idea...  I've missed almost all the context here.
> 
> > The context was that I found we lack a way to simply express the need
> > for one driver to get a value from an EEPROM-like device, for example to
> > get a MAC Address, or a serial number, in a generic way, without having
> > to poke directly with some custom function that would be exported by the
> > EEPROM driver.
> 
> This sort of information is often stored in places like flash partitions
> too.  Are we sure that regmap is a good place to be hooking in here?
> The use case is sane, and being able to use regmap to do some of it
> seems sensible (I've seen people use OTP in PMICs for similar purposes)
> but perhaps an additional layer of abstraction on top makes sense.

Ah, I didn't thought it could be stored into a partition. Ok, so using
an intermediate abstraction for this makes sense (probably using regmap
for all the accesses that are relevant, like i2c, spi or mmio)

> > What we've been discussing so far is that:
> >   - To have a common framework we could base our work on, we could move
> >     the EEPROM drivers from drivers/misc/eeprom to MTD
> >   - To declare the ranges that needed to be used by a driver that was
> >     needing a value from one of those MTD drivers, we would use regmap
> >     with a MTD backend
> >   - And since we actually need to declare which ranges and in which
> >     device one driver would have to retrieve this value from, we were
> >     actually in need of DT bindings.
> 
> > This is pretty much the only context involved, and we are at the early
> > stage of the discussion, so any comment is very welcome :)
> 
> If this stuff is being represented in MTD doesn't MTD already have
> adequate abstractions for saying "this region in flash".  But otherwise
> this seems fine, it's not a generic regmap DT binding but instead rather
> more specific than that.

Yes, since we seem to be going to a point where regmap will be a
convenience in this case, we probably won't need a generic regmap
binding, but rather a generic way to define a range and offset into a
referenced device.

Arnd, the others, is this ok for you?

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

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