From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752637AbeCTKRn (ORCPT ); Tue, 20 Mar 2018 06:17:43 -0400 Received: from mx08-00178001.pphosted.com ([91.207.212.93]:46743 "EHLO mx07-00178001.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752097AbeCTKRi (ORCPT ); Tue, 20 Mar 2018 06:17:38 -0400 Subject: Re: [RESEND PATCH v1 2/6] i2c: i2c-stm32f7: Add slave support To: Wolfram Sang CC: Maxime Coquelin , Alexandre Torgue , , , References: <1520852023-27083-1-git-send-email-pierre-yves.mordret@st.com> <1520852023-27083-3-git-send-email-pierre-yves.mordret@st.com> <20180317205109.gocf5wemtjkyomct@ninjato> <5a3c5b21-bc66-ce73-a997-f686ecc275f3@st.com> <20180320095242.tedafu5wphsx55qx@katana> From: Pierre Yves MORDRET Message-ID: Date: Tue, 20 Mar 2018 11:17:21 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0 MIME-Version: 1.0 In-Reply-To: <20180320095242.tedafu5wphsx55qx@katana> Content-Type: text/plain; charset="windows-1252" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.75.127.50] X-ClientProxiedBy: SFHDAG2NODE3.st.com (10.75.127.6) To SFHDAG5NODE2.st.com (10.75.127.14) X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2018-03-20_04:,, signatures=0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03/20/2018 10:52 AM, Wolfram Sang wrote: > >> I do believe the hw can support it, even it looks odd to me having the same I2C >> in slave and master mode at the same time. > > I2C is multi-master, so it is perfectly valid for a device to be master > and slave. I do have seen designs making use of that more than once. > >> Nevertheless the driver is devised to support either master or slave more but >> not at the same time. > > Why should we limit ourselves here? Also, why should we have an > unnecessary configuration option? > > Unless the HW is broken and does not support it, I usually don't accept > slave-only solutions. If the needs for master and slave arises later, > this is hard to refactor and better done properly right away. > > Is it so hard? Usually you have irqs for master and for slave seperated, > so you can code things quite orthogonal. Check de20d1857dd6 ("i2c: rcar: > add slave support") as an example. > I need to check at my end but status bits are shared between master and slave in my IP: i.e. Tx Empty, Rx Empty, NAxk, Stop. Both bits have a meaning in either master and slave mode. In your case status bits are separated between master and slave. BTW I need to think about it.