linux-kernel - Re: [RESEND RFC 2/3] nvmem: Add 'nvmem-blob' driver

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Message-ID: <CAHQ1cqHL=HG_R-hBgUxSGr=XcYRepQTxU9n1zKVfg=L4bENVHg@mail.gmail.com>
Date:	Mon, 7 Mar 2016 20:07:41 -0800
From:	Andrey Smirnov <andrew.smirnov@...il.com>
To:	Maxime Ripard <maxime.ripard@...e-electrons.com>
Cc:	Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
	linux-kernel@...r.kernel.org,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Trent Piepho <tpiepho@...etacorp.com>
Subject: Re: [RESEND RFC 2/3] nvmem: Add 'nvmem-blob' driver

>> >
>> > Patch itself looks simple. Before we review it further could you provide
>> > more details on the exact usecase or some background of this.
>>
>> The discussion on this topic originated on mailing list of Barebox
>> project(which borrows very heavily from Linux designs). Barebox
>> operates on two device tree blobs, one is used for its internal
>> initialization, whereas second one is passed to Linux kernel when
>> booting it. The problem I was trying to solve was to make possible to
>> specify in the first DT blob what data would be used for MAC address
>> fixup of the second DT blob(the one passed to Linux).
>>
>> My first approach was to implement a very limited DT code, however in
>> discussing it the consensus was that porting 'nvmem' subsystem from
>> the kernel and using for the same purpose would be a better approach.
>> First pass adoption of that subsystem revealed that there were two
>> use-cases that current design didn't allow us to handle:
>>
>> - Depending on the version i.MX SoC MAC address data stored in ROM
>> would have different layout so as a possible solution to that I
>> implemented "composite" driver(patch #3)
>>
>> - On i.MX28, part of the MAC address is hard-coded in
>> arch/arm/mach-mxs/mach-mxs.c and only a portion of it is read from
>> ROM, this patch in combination with the aforementioned one should
>> allow us to encode all needed info in DT.
>>
>> Ideally, since all of the above is as applicable to Linux as it is to
>> Barebox it would be good for BB not to invent its own custom 'nvmem'
>> flavor, so hence me trying to start a conversation about adding this
>> upstream.
>
> If the only use-case is to store the MAC address, why not using the
> local-mac-address property directly?

I don't think I understand what you mean, could you give me an example
of how I'd use local-mac-address property for that use case? AFAIK,
local-mac-address is just an array of bytes embedded into device tree,
how would it get populated with data from OTP memory of SoC?