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

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Message-ID: <1416305221.4982.23.camel@mhfsdcap03>
Date:	Tue, 18 Nov 2014 18:07:01 +0800
From:	xudong chen <xudong.chen@...iatek.com>
To:	Wolfram Sang <wsa@...-dreams.de>
CC:	Mark Rutland <mark.rutland@....com>,
	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

On Fri, 2014-11-14 at 11:12 +0800, xudong chen wrote:
> On Thu, 2014-11-13 at 19:31 +0100, Wolfram Sang wrote:
> > > 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?
> 
> This is the HW limitation, we will try to workaround this in the
> separate patch.
> 
Except limited RS and limited length support, our HW follow I2C protocol
spec.
The length is compatible with most I2C devices, only a few I2C devices
need transfer more than 255 bytes.
The future Mediatek IC will fix the RS and length limitation.

Thanks!
> 
> 


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