linux-kernel - Re: [PATCH RFC] eeprom: at24: extend driver to plug into the NVMEM framework

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Message-ID: <20150820163851.GG27457@lunn.ch>
Date:	Thu, 20 Aug 2015 18:38:51 +0200
From:	Andrew Lunn <andrew@...n.ch>
To:	Maxime Ripard <maxime.ripard@...e-electrons.com>
Cc:	Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
	Stefan Wahren <stefan.wahren@...e.com>,
	linux-kernel@...r.kernel.org, linux-i2c@...r.kernel.org,
	wsa@...-dreams.de
Subject: Re: [PATCH RFC] eeprom: at24: extend driver to plug into the NVMEM
 framework

> It's true that this is something that we might have overlooked. Is it
> expected to maintain that compatibility when moving a driver from one
> framework to another (and this is a real question, not a troll)?

Yes. There will be user space applications reading from the eeprom
file in /sys. In fact, until the NVMEM framework arrived, it was not
easy to access the eeprom from kernel space, meaning the majority of
users must of been user space...

> If so, we might provide a compatibility layer to add the former file
> too, protected by a kconfig option maybe ?

There is one other detail you might of missed. Both AT24 and AT25 do
have an in kernel API. In the at24_platform_data you can have a
callback function "setup" which gets called when the device is
probed. setup() is called with a struct memory_accessor which contains
function pointers for reading and writing to the EEPROM. A few
platforms use these for getting the MAC address out of the EEPROM.
And these platforms are old style, not DT.

    Andrew
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