linux-kernel - Re: [PATCH 2/3] i2c: slave-eeprom: add eeprom simulator driver

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Date:	Wed, 26 Nov 2014 13:49:01 +0100
From:	Wolfram Sang <wsa@...-dreams.de>
To:	Alexander Kochetkov <al.kochet@...il.com>
Cc:	Stijn Devriendt <highguy@...il.com>, linux-i2c@...r.kernel.org,
	linux-sh@...r.kernel.org, Magnus Damm <magnus.damm@...il.com>,
	Simon Horman <horms@...ge.net.au>,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-arm-kernel@...ts.infradead.org,
	Jean Delvare <jdelvare@...e.de>
Subject: Re: [PATCH 2/3] i2c: slave-eeprom: add eeprom simulator driver

On Wed, Nov 26, 2014 at 03:25:29PM +0300, Alexander Kochetkov wrote:
> 
> 22 нояб. 2014 г., в 21:12, Wolfram Sang <wsa@...-dreams.de> написал(а):
> 
> > IMO a repeated start is to ensure that two messages arrive at the slave
> > without interruption from another master. I can't think why a slave
> > should know which type of start that was. In fact, if it does that would
> > raise an eyebrow for me. Do you have an example?
> 
> It is used to implement Device ID reading.

Yes and no, I'd say :) Technically, it needs repeated start. But really,
the hardware should handle this (and I know one IP core which has
support for it). One could try to simulate the behaviour in the bus
driver IF a second slave address AND detection of repeated start is
available, but I doubt this combination exists.

Still, all the _slave driver_ needs to handle is an
I2C_SLAVE_EVENT_DEVICE_ID which should return the apropriate value.

That being said, I have never seen querying Device ID in action.

> Not sure, that the feature is really needed for the first release.

I am sure it is not :D

Thanks,

   Wolfram


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