From mboxrd@z Thu Jan 1 00:00:00 1970 From: xudong chen Subject: Re: [PATCH v2 0/3] ARM: mediatek: Add driver for Mediatek I2C controller Date: Tue, 18 Nov 2014 18:07:01 +0800 Message-ID: <1416305221.4982.23.camel@mhfsdcap03> References: <1415078977-18374-1-git-send-email-xudong.chen@mediatek.com> <20141113183122.GH1275@katana> <1415934752.2152.58.camel@mhfsdcap03> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1415934752.2152.58.camel@mhfsdcap03> Sender: devicetree-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Wolfram Sang Cc: Mark Rutland , Matthias Brugger , srv_heupstream-NuS5LvNUpcJWk0Htik3J/w@public.gmane.org, Sascha Hauer , Rob Herring , Pawel Moll , Ian Campbell , Kumar Gala , Russell King , Grant Likely , Jean Delvare , Arnd Bergmann , devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, linux-i2c-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Yingjoe Chen , Eddie Huang , Nathan Chung , YH Chen List-Id: devicetree@vger.kernel.org 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! > > -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html