linux-kernel - Re: [RFC PATCH 1/3] eeprom: Add a simple EEPROM framework

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Date:	Sun, 22 Feb 2015 15:32:11 +0100
From:	Maxime Ripard <maxime.ripard@...e-electrons.com>
To:	Rob Herring <robherring2@...il.com>
Cc:	Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Kumar Gala <galak@...eaurora.org>,
	"linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Stephen Boyd <sboyd@...eaurora.org>,
	Arnd Bergmann <arnd@...db.de>, Mark Brown <broonie@...nel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [RFC PATCH 1/3] eeprom: Add a simple EEPROM framework

On Fri, Feb 20, 2015 at 04:01:55PM -0600, Rob Herring wrote:
> [...]
> 
> >>> += Data consumers =
> >>> +
> >>> +Required properties:
> >>> +
> >>> +eeproms: List of phandle and data cell specifier triplet, one triplet
> >>> +        for each data cell the device might be interested in. The
> >>> +        triplet consists of the phandle to the eeprom provider, then
> >>> +        the offset in byte within that storage device, and the length
> >>> +        in byte of the data we care about.
> >>
> >>
> >> The problem with this is it assumes you know who the consumer is and
> >> that it is a DT node. For example, how would you describe a serial
> >> number?
> >
> > Correct me if I miss understood.
> > Is serial number any different?
> > Am hoping that the eeprom consumer would be aware of offset and size of
> > serial number in the eeprom
> >
> > Cant the consumer do:
> >
> > eeprom-consumer {
> >         eeproms = <&at24 0 4>;
> >         eeprom-names = "device-serial-number";
> 
> Yes, but who is "eeprom-consumer"?

Any device that should lookup values in one of the EEPROM.

> DT nodes generally describe a h/w block, but it this case, the
> consumer depends on the OS, not the h/w. 

Not really, or at least, not more than any similar binding we
currently have.

The fact that a MAC-address for the first ethernet chip is stored at a
given offset in a given eeprom has nothing to do with the OS.

> I'm not saying you can't describe where things are, but I don't
> think you should imply who is the consumer and doing so is
> unnecessarily complicated.

If you only take the case of a serial number, indeed. If you take
other usage into account, you can't really do without it.

> Also, the layout of EEPROM is likely very much platform specific.

Indeed, which is why it should be in the DT.

> Some could have a more complex structure perhaps with key ids and
> linked list structure.

Then just request the size of the whole list, and parse it afterwards
in your driver?

> I would do something more simple that is just a list of keys and their
> location like this:
> 
> device-serial-number = <start size>;
> key1 = <start size>;
> key2 = <start size>;

I'm sorry, but what's the difference?

Maxime

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

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