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

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Date:	Mon, 23 Feb 2015 10:15:59 +0100
From:	Sascha Hauer <s.hauer@...gutronix.de>
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>,
	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	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:
> On Fri, Feb 20, 2015 at 1:25 PM, Srinivas Kandagatla
> <srinivas.kandagatla@...aro.org> wrote:
> >
> >
> > On 20/02/15 17:21, Rob Herring wrote:
> >>
> >> On Thu, Feb 19, 2015 at 11:08 AM, Srinivas Kandagatla
> >> <srinivas.kandagatla@...aro.org> wrote:
> >>>
> >>> From: Maxime Ripard <maxime.ripard@...e-electrons.com>
> >>>
> >>> Up until now, EEPROM drivers were stored in drivers/misc, where they all
> >>> had to
> >>> duplicate pretty much the same code to register a sysfs file, allow
> >>> in-kernel
> >>> users to access the content of the devices they were driving, etc.
> >>>
> >>> This was also a problem as far as other in-kernel users were involved,
> >>> since
> >>> the solutions used were pretty much different from on driver to another,
> >>> there
> >>> was a rather big abstraction leak.
> >>>
> >>> This introduction of this framework aims at solving this. It also
> >>> introduces DT
> >>> representation for consumer devices to go get the data they require (MAC
> >>> Addresses, SoC/Revision ID, part numbers, and so on) from the EEPROMs.
> >>>
> >>> Having regmap interface to this framework would give much better
> >>> abstraction for eeproms on different buses.
> >>>
> >>> Signed-off-by: Maxime Ripard <maxime.ripard@...e-electrons.com>
> >>> [srinivas.kandagatla: Moved to regmap based and cleanedup apis]
> >>> Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
> >>> ---
> >>>   .../devicetree/bindings/eeprom/eeprom.txt          |  48 ++++
> >>>   drivers/Kconfig                                    |   2 +
> >>>   drivers/Makefile                                   |   1 +
> >>>   drivers/eeprom/Kconfig                             |  19 ++
> >>>   drivers/eeprom/Makefile                            |   9 +
> >>>   drivers/eeprom/core.c                              | 290
> >>> +++++++++++++++++++++
> >>>   include/linux/eeprom-consumer.h                    |  73 ++++++
> >>>   include/linux/eeprom-provider.h                    |  51 ++++
> >>
> >>
> >> Who is going to be the maintainer for this?
> >
> >
> > Am happy to be one.
> 
> So please add a MAINTAINERS entry.
> 
> [...]
> 
> >>> += 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"? DT nodes generally describe a h/w
> block, but it this case, the consumer depends on the OS, not the h/w.
> 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.
> 
> Also, the layout of EEPROM is likely very much platform specific. Some
> could have a more complex structure perhaps with key ids and linked
> list structure.
> 
> 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>;

Maybe better a node instead of a property. That would allow to use the
standard reg property to describe the position in the eeprom. Also it
would give consumers in dt a possibility to use a phandle to point to a
variable:

	serial_number: var@c {
		reg = <0xc 0x8>;
		name = <?>;
	};

Sascha

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