linux-kernel - Re: [Question] When should a driver issue STOP condition?

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Message-ID: <20180831095356.ow6nhbx2fhhpuhjj@ninjato>
Date:   Fri, 31 Aug 2018 11:53:56 +0200
From:   Wolfram Sang <wsa@...-dreams.de>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:     linux-i2c@...r.kernel.org,
        Wolfram Sang <wsa+renesas@...g-engineering.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [Question] When should a driver issue STOP condition?

> The problem is, my driver is forcibly setting
> STOP condition unless the next message is read.

This likely is a problem.

In Linux I2C terminology, a transfer is everything between a START and a
STOP. A transfer may consist of multiple messages, connected with
REP_START [1].

So, a STOP should be generated after the last message of a transfer or
of I2C_M_STOP is set in a message. The latter should be super-rare
because mostly you should be able to use multiple transfers with a
regular STOP instead.

[1] Slide 8 illustrates this:
http://events17.linuxfoundation.org/sites/events/files/slides/ELCE17-WSang-I2C-Fault-Injector.pdf

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