[RFC PATCH 1/3] eeprom: Add a simple EEPROM framework

Sascha Hauer
2015-02-23T09:15:59Z

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@linaro.org> wrote:
> >
> >
> > On 20/02/15 17:21, Rob Herring wrote:
> >>
> >> On Thu, Feb 19, 2015 at 11:08 AM, Srinivas Kandagatla
> >> <srinivas.kandagatla@linaro.org> wrote:
> >>>
> >>> From: Maxime Ripard <maxime.ripard@free-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@free-electrons.com>
> >>> [srinivas.kandagatla: Moved to regmap based and cleanedup apis]
> >>> Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.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 at c {
reg = <0xc 0x8>;
name = <?>;
};

Sascha

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