linux-kernel - Re: [PATCH 2/6] nvmem: Add backwards compatibility support for older EEPROM drivers.

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Date:	Fri, 11 Dec 2015 14:03:25 +0100
From:	Wolfram Sang <wsa@...-dreams.de>
To:	Andrew Lunn <andrew@...n.ch>
Cc:	GregKH <greg@...ah.com>, srinivas.kandagatla@...aro.org,
	maxime.ripard@...e-electrons.com, broonie@...nel.org, vz@...ia.com,
	afd@...com, linux-kernel@...r.kernel.org,
	Pantelis Antoniou <pantelis.antoniou@...sulko.com>
Subject: Re: [PATCH 2/6] nvmem: Add backwards compatibility support for older
 EEPROM drivers.

On Tue, Dec 08, 2015 at 03:05:07PM +0100, Andrew Lunn wrote:
> Older drivers made an 'eeprom' file available in the /sys device
> directory. Have the NVMEM core provide this to retain backwards
> compatibility.
> 
> Signed-off-by: Andrew Lunn <andrew@...n.ch>
> ---
>  drivers/nvmem/Kconfig          |  7 ++++
>  drivers/nvmem/core.c           | 75 +++++++++++++++++++++++++++++++++++++++---
>  include/linux/nvmem-provider.h | 10 ++++++
>  3 files changed, 88 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/nvmem/Kconfig b/drivers/nvmem/Kconfig
> index bc4ea585b42e..b4e79ba7d502 100644
> --- a/drivers/nvmem/Kconfig
> +++ b/drivers/nvmem/Kconfig
> @@ -13,6 +13,13 @@ menuconfig NVMEM
>  	  If unsure, say no.
>  
>  if NVMEM
> +config NVMEM_COMPAT
> +       bool "Enable /sys compatibility with old eeprom drivers"
> +       help
> +	 Older EEPROM drivers, such as AT24, AT25, provide access to
> +	 the eeprom via a file called "eeprom" in /sys under the
> +	 device node. Enabling this option makes the NVMEM core
> +	 provide this file to retain backwards compatibility

I don't like this being a Kconfig option TBH. In most cases, when I read
"retain backwards compatibility" in Kconfig help texts, I keep the
option activated because I don't know the details when exactly it is
safe to disable it. Plus, we have too many Kconfig symbols already.

I suggest to add this flag to nvmem_config and let the old eeprom
drivers always set this flag because they need to provide this file for
some more time, if not forever. New drivers using the nvmem_layer will
probably not want to set this.

BTW how does this NVMEM framework relate to the memory_accessor
framework. Can it be used to replace it? I think we should keep the
number of eeprom interfaces at a sane level, preferably 1 ;)

Also adding Pantelis to CC who also submitted at24 NVMEM support a while
ago.

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