linux-kernel - Re: [RFC 0/3] drivers: Add an API to read device specific config data

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Date:   Mon, 27 Feb 2017 21:42:30 +0100
From:   Boris Brezillon <boris.brezillon@...e-electrons.com>
To:     Alban <albeu@...e.fr>
Cc:     linux-kernel@...r.kernel.org, linux-mtd@...ts.infradead.org,
        Cyrille Pitchen <cyrille.pitchen@...el.com>,
        Richard Weinberger <richard@....at>,
        Marek Vasut <marek.vasut@...il.com>,
        Brian Norris <computersforpeace@...il.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Moritz Fischer <moritz.fischer@...us.com>
Subject: Re: [RFC 0/3] drivers: Add an API to read device specific config
 data

+Moritz

Hi Alban,

On Mon, 27 Feb 2017 21:28:09 +0100
Alban <albeu@...e.fr> wrote:

> Hi all,
> 
> while looking at adding OF support for the ath9k driver I had the problem of
> reading the EEPROM data. On the SoC platforms this data is stored in an SPI
> flash along with a few other things. In OpenWRT/LEDE this data is read from
> the board init code using the fact that the flash is (normaly) readable from
> a memory map. A bit too hackish for my taste.
> 
> This is just one example, there is various other similar cases, mostly with
> MAC addresses. I thought it would be nicer if we had a clean API for this,
> similar to the firmware API but per device instance instead of beeing per
> driver. The device driver wouldn't have to care where the data is stored,
> they just request it and the backend take care of reading the EEPROM, MTD
> or whatever is used on the board.
> 
> This series implement such an API along with an implementation for MTD
> devices and a use in the ath9k driver. As this is an RFC I didn't yet
> write the OF binding documentation, that will come later if the feedback
> is positive.

What you're looking for already exists and it's called nvmem[1]. Some
work has been done to expose MTD partitions as nvmem cells [2], but
it's never been finished.
Can you please finish Moritz implementation instead of creating a new
API?

Thanks,

Boris

[1]http://lxr.free-electrons.com/source/Documentation/nvmem/nvmem.txt
[2]https://patchwork.ozlabs.org/patch/626460/