linux-kernel - Re: [PATCH V7 3/6] i2c: qup: Transfer each i2c_msg in i2c

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Message-ID: <20160124112915.GA1775@katana>
Date:	Sun, 24 Jan 2016 12:29:16 +0100
From:	Wolfram Sang <wsa@...-dreams.de>
To:	Sricharan R <sricharan@...eaurora.org>
Cc:	devicetree@...r.kernel.org, linux-arm-msm@...r.kernel.org,
	agross@...eaurora.org, linux-kernel@...r.kernel.org,
	linux-i2c@...r.kernel.org, iivanov@...sol.com,
	galak@...eaurora.org, dmaengine@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, andy.gross@...aro.org,
	ntelkar@...eaurora.org, architt@...eaurora.org
Subject: Re: [PATCH V7 3/6] i2c: qup: Transfer each i2c_msg in i2c_msgs
 without a stop bit

Hi,

> "If this is the last message in a group, it is followed by a STOP.
> Otherwise it is followed by the next @i2c_msg transaction segment,
> beginning with a (repeated) START"

This is correct.

> So the expectation is that there is no 'STOP' bit inbetween individual
> i2c_msg segments with repeated 'START'. The QUP i2c hardware has no way
> to inform that there should not be a 'STOP' at the end of transaction.
> The only way to implement this is to coalesce all the i2c_msg in i2c_msgs
> in to one transaction and transfer them. Adding the support for the same.

So, there will not be a REP_START condition on the bus? I am sorry to
say that I can't accept this. A REP_START is a REP_START and nothing
else. There are devices which will get confused if there is no real
REP_START condition.

Without knowing the HW in detail, can't you implement I2C_M_NOSTART and
let the touchscreen driver use it via regmap? That would be the proper
way (from what I understand).

Regards,

   Wolfram


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