From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S968656AbcA1E5U (ORCPT ); Wed, 27 Jan 2016 23:57:20 -0500 Received: from smtp.codeaurora.org ([198.145.29.96]:34646 "EHLO smtp.codeaurora.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S967495AbcA1E5P (ORCPT ); Wed, 27 Jan 2016 23:57:15 -0500 From: "Sricharan" To: "'Wolfram Sang'" Cc: , , , , , , , , , , , References: <1453197766-18976-1-git-send-email-sricharan@codeaurora.org> <1453197766-18976-4-git-send-email-sricharan@codeaurora.org> <20160124112915.GA1775@katana> In-Reply-To: <20160124112915.GA1775@katana> Subject: RE: [PATCH V7 3/6] i2c: qup: Transfer each i2c_msg in i2c_msgs without a stop bit Date: Thu, 28 Jan 2016 10:27:05 +0530 Message-ID: <001401d15988$59f6dcf0$0de496d0$@codeaurora.org> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit X-Mailer: Microsoft Outlook 15.0 Thread-Index: AQHBrzqT1wRAKGgXA8TA5/snlKrqvgH3sPWfANSC3j+fGUkQsA== Content-Language: en-us Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Wolfram, > -----Original Message----- > From: Wolfram Sang [mailto:wsa@the-dreams.de] > Sent: Sunday, January 24, 2016 4:59 PM > To: Sricharan R > Cc: devicetree@vger.kernel.org; linux-arm-msm@vger.kernel.org; > agross@codeaurora.org; linux-kernel@vger.kernel.org; linux- > i2c@vger.kernel.org; iivanov@mm-sol.com; galak@codeaurora.org; > dmaengine@vger.kernel.org; linux-arm-kernel@lists.infradead.org; > andy.gross@linaro.org; ntelkar@codeaurora.org; architt@codeaurora.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). Ah, so what I meant above is there is no 'STOP' bit between each msg in i2c_msgs, but 'REAPEATED_START' still holds true. We are sending 'START' bit for each msg. So these is how each msg in i2c_msg is sent, |------MSG1--------|-----MSG2---------|------MSG3------------| |START|DATA|------|START|DATA|---|START|DATA|STOP| If my commit text does not make this clear, I can reword that ? Regards, Sricharan