linux-kernel - Re: [RESEND PATCH v2 0/9] eeprom: at24: at24cs series serial number read

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Date:	Sat, 2 Jan 2016 21:50:41 +0100
From:	Wolfram Sang <wsa@...-dreams.de>
To:	Bartosz Golaszewski <bgolaszewski@...libre.com>
Cc:	linux-i2c <linux-i2c@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RESEND PATCH v2 0/9] eeprom: at24: at24cs series serial number
 read

On Fri, Dec 11, 2015 at 02:55:10PM +0100, Bartosz Golaszewski wrote:
> 2015-12-11 13:08 GMT+01:00 Wolfram Sang <wsa@...-dreams.de>:
> > On Wed, Dec 02, 2015 at 11:25:17AM +0100, Bartosz Golaszewski wrote:
> >> Chips from the at24cs EEPROM series have an additional read-only memory area
> >> containing a factory pre-programmed serial number. In order to access it, a
> >> dummy write must be executed before reading the serial number bytes.
> >
> > Can't you instantiate a read-only EEPROM on this second address? Or a
> > seperate driver attaching to this address? What is the advantage of
> > having this in at24?
> >
> 
> The regular memory area and serial number read-only block share the
> internal address pointer. We must ensure that there's no race
> conditions between normal EEPROM reads/writes and serial number reads.

I don't get it. Both, regular at24 reads and the serial read, setup the
pointer every time by using two messages, first write to set the
pointer, then read. The per-adapter lock makes sure those two messages
will not get interrupted. So, it looks to me that it would be OK if a
serial read access gets inbetween a eeprom read access. Am I wrong?


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