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

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Date:	Fri, 20 Feb 2015 16:01:55 -0600
From:	Rob Herring <robherring2@...il.com>
To:	Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
Cc:	"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 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>;

Rob
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