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

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Message-ID: <20160309095856.GM8418@lukather>
Date:	Wed, 9 Mar 2016 10:58:56 +0100
From:	Maxime Ripard <maxime.ripard@...e-electrons.com>
To:	Andrey Smirnov <andrew.smirnov@...il.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

On Tue, Mar 08, 2016 at 02:46:52PM -0800, Andrey Smirnov wrote:
> >>
> >> 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,
> >
> > Well, yeah, but the nvmem-blob is also just an array of bytes embedded
> > into the DT, right?
> 
> One is accessible via "nvmem" API and the other one isn't.

But there's no point in accessing it with nvmem in the first
place. You want to provide some information to the ethernet driver to
give it his mac address, that's what you want to do. And we already
have a property that does just that, and is supported by all the
ethernet drivers. Why would you want to add a special case to
something that is doing exactly the same thing?

> >> how would it get populated with data from OTP memory of SoC?
> >
> > In the bootloader, or Linux, read the OTP, patch the DT to add that
> > node, done.
> 
> No, it's not really "done", because if you read my previous messages,
> "read the OTP, patch the DT" is exactly the problem I am trying to
> solve. The overall goal is to be able to read a certain "nvmem" cell
> and patch DT with that data as MAC address,

But *why* do you need to store that using nvmem in the first place?
You really have two solutions here: make your ethernet driver read the
EEPROM using nvmem directly or do it in the bootloader and set
local-mac-address (note that you can do both).

> however in it's current incarnation "nvmem" doesn't have provisions
> to make cells that are just combination of other cells (patch #3)

This use case is valid.

> and to embed certain data in DT and then access it as "nvmem" cell
> (patch #2)

And this one is redundant.

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

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