From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758781AbaKUPeA (ORCPT ); Fri, 21 Nov 2014 10:34:00 -0500 Received: from comal.ext.ti.com ([198.47.26.152]:33538 "EHLO comal.ext.ti.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758691AbaKUPd5 (ORCPT ); Fri, 21 Nov 2014 10:33:57 -0500 Message-ID: <546F5B51.1030006@ti.com> Date: Fri, 21 Nov 2014 17:33:37 +0200 From: Grygorii Strashko User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.2.0 MIME-Version: 1.0 To: =?windows-1252?Q?Uwe_Kleine-K=F6nig?= CC: Wolfram Sang , , , Sekhar Nori , Kevin Hilman , Santosh Shilimkar , Murali Karicheri Subject: Re: [2/5] i2c: davinci: query STP always when NACK is received References: <1416477788-5544-3-git-send-email-grygorii.strashko@ti.com> <20141120221953.GI27002@pengutronix.de> <546F34B9.1000206@ti.com> <20141121131008.GQ27002@pengutronix.de> In-Reply-To: <20141121131008.GQ27002@pengutronix.de> Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Uwe, On 11/21/2014 03:10 PM, Uwe Kleine-König wrote: > On Fri, Nov 21, 2014 at 02:48:57PM +0200, Grygorii Strashko wrote: >> On 11/21/2014 12:19 AM, Uwe Kleine-König wrote: >>>> diff --git a/drivers/i2c/busses/i2c-davinci.c b/drivers/i2c/busses/i2c-davinci.c >>>> index 9bbfb8f..2cef115 100644 >>>> --- a/drivers/i2c/busses/i2c-davinci.c >>>> +++ b/drivers/i2c/busses/i2c-davinci.c >>>> @@ -411,11 +411,9 @@ i2c_davinci_xfer_msg(struct i2c_adapter *adap, struct i2c_msg *msg, int stop) >>>> if (dev->cmd_err & DAVINCI_I2C_STR_NACK) { >>>> if (msg->flags & I2C_M_IGNORE_NAK) >>>> return msg->len; >>>> - if (stop) { >>>> - w = davinci_i2c_read_reg(dev, DAVINCI_I2C_MDR_REG); >>>> - w |= DAVINCI_I2C_MDR_STP; >>>> - davinci_i2c_write_reg(dev, DAVINCI_I2C_MDR_REG, w); >>>> - } >>>> + w = davinci_i2c_read_reg(dev, DAVINCI_I2C_MDR_REG); >>>> + w |= DAVINCI_I2C_MDR_STP; >>>> + davinci_i2c_write_reg(dev, DAVINCI_I2C_MDR_REG, w); >>> I think this is a good change, but I wonder if the handling of >>> I2C_M_IGNORE_NAK is correct here. If the controller reports a NACK say >>> for the 2nd byte of a 5-byte-message, the transfer supposed to >>> continue, right? (Hmm, maybe the framework handle this and restarts the >>> transfer with I2C_M_NOSTART but the davinci driver doesn't seem to >>> handle this flag?) >> >> Have nothing to say about handling of I2C_M_IGNORE_NAK. I'm not going to >> change current behavior - davinci driver will interrupt transfer of i2c_msg always >> in case of NACK and start transfer of the next i2c_msg (if exist). >> In my opinion, Above question is out of scope of this patch. > Yeah right, that's exactly what I thought. > > Thinking again I wonder if with your change handling is correct when the > sender wants to do a repeated start. That would need a more detailed > look into the driver. Davinci driver will always abort transfer with error -EREMOTEIO in case if NACK received from I2C slave device. And the next omap_i2c_xfer() call may be *not* targeted to the same I2C slave device. ^ if !I2C_M_IGNORE_NAK This discussion is absolutely similar to https://lkml.org/lkml/2013/7/16/235 So, I'm just copy-pasting my answers from there ;) regards, -grygorii