linux-kernel - Re: [PATCH v2 0/3] ARM: mediatek: Add driver for Mediatek I2C controller

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Date:	Thu, 13 Nov 2014 19:31:22 +0100
From:	Wolfram Sang <wsa@...-dreams.de>
To:	Xudong Chen <xudong.chen@...iatek.com>
Cc:	Mark Rutland <mark.rutland@....com>, arm@...nel.org,
	Matthias Brugger <matthias.bgg@...il.com>,
	srv_heupstream@...iatek.com, Sascha Hauer <kernel@...gutronix.de>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Russell King <linux@....linux.org.uk>,
	Grant Likely <grant.likely@...aro.org>,
	Jean Delvare <jdelvare@...e.de>, Arnd Bergmann <arnd@...db.de>,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-i2c@...r.kernel.org,
	Yingjoe Chen <yingjoe.chen@...iatek.com>,
	Eddie Huang <eddie.huang@...iatek.com>,
	Nathan Chung <nathan.chung@...iatek.com>,
	YH Chen <yh.chen@...iatek.com>
Subject: Re: [PATCH v2 0/3] ARM: mediatek: Add driver for Mediatek I2C
 controller


> MTK I2C HW has some limitation.
> 1. If the i2c_msg number is more than one, STOP will be issued instead of
> RS(Repeat Start) between each message.
> 
> 2. Mediatek I2C controller support WRRD(write then read) mode, in WRRD
> mode the Repeat Start will be issued between 2 messages.
> In this driver if 2 messages is first write then read, the driver will
> combine 2 messages using Write-Read mode so the RS will be issued between
> the 2 messages.
> Ex: W/R/R, driver will combine first W/R and then R.
> 
> 3. Due to HW limitation, in this version the max transfer data length is 255
> in one message.

This looks to me more like an SMBUS controller instead of I2C. Maybe you
should populate smbus_xfer rather than master_xfer?

> MT8135 and MT6589 can control I2C pins on PMIC(MT6397) by setting the i2c
> registers in MT8135 side.

I still didn't get this, even after reading the mail thread of old
series. Can someone maybe draw me a nice ASCII picture showing the setup
which is going on here?


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