linux-kernel - Re: [PATCH] eeprom: at24: Add support for large EEPROMs connected to SMBus adapters

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Message-ID: <20150204174723.GB30930@katana>
Date:	Wed, 4 Feb 2015 18:47:23 +0100
From:	Wolfram Sang <wsa@...-dreams.de>
To:	Guenter Roeck <linux@...ck-us.net>
Cc:	linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] eeprom: at24: Add support for large EEPROMs connected to
 SMBus adapters

On Wed, Feb 04, 2015 at 08:23:37AM -0800, Guenter Roeck wrote:
> Large EEPROMS (24c32 and larger) require a two-byte data address
> instead of just a single byte. Implement support for such EEPROMs
> with SMBus commands.
> 
> Support has limitations (reads are not multi-master safe) and is slow,
> but it works. Practical use is for a system with 24c32 connected to
> Intel 82801I (ICH9).

Can't you simply use i2c-dev to access the EEPROM? In multi-master
environments, things can really go wrong, so I wouldn't like to add
something dangerous by default. Maybe with a module parameter named
"allow-multimaster-unsafe-access-to-large-eeproms-with-smbus" which is
default off. But I'd really prefer the i2c-dev solution. Hooking a 16bit
EEPROM to SMBus is daring, after all. SMBus is multi-master, too.

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