From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4BB1BC433C1 for ; Wed, 24 Mar 2021 04:01:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id ED5A2619B2 for ; Wed, 24 Mar 2021 04:01:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229616AbhCXEA5 (ORCPT ); Wed, 24 Mar 2021 00:00:57 -0400 Received: from mga07.intel.com ([134.134.136.100]:48631 "EHLO mga07.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229629AbhCXEAn (ORCPT ); Wed, 24 Mar 2021 00:00:43 -0400 IronPort-SDR: BDFSa1Y8cCUSlYbSu8icOxk6amP05yT1kZe6n03xxXmq4yF/Ef36jZV9Xuk8BD3x+AcvZJn/0X d3N6NCP89fUA== X-IronPort-AV: E=McAfee;i="6000,8403,9932"; a="254619851" X-IronPort-AV: E=Sophos;i="5.81,272,1610438400"; d="scan'208";a="254619851" Received: from fmsmga002.fm.intel.com ([10.253.24.26]) by orsmga105.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 23 Mar 2021 21:00:41 -0700 IronPort-SDR: 2PFRo5AZLe+Q+e8VW5HKphckol1bSAXhX/pCaaXJKdVwlXhSsFVgscRrsav8C5Ln97JDY0R+3J HloNnkom3wUg== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.81,272,1610438400"; d="scan'208";a="442027086" Received: from unknown (HELO [10.239.154.55]) ([10.239.154.55]) by fmsmga002.fm.intel.com with ESMTP; 23 Mar 2021 21:00:34 -0700 Subject: Re: [PATCH v10] i2c: virtio: add a virtio i2c frontend driver To: Viresh Kumar Cc: linux-i2c@vger.kernel.org, virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org, mst@redhat.com, wsa@kernel.org, jasowang@redhat.com, wsa+renesas@sang-engineering.com, andriy.shevchenko@linux.intel.com, conghui.chen@intel.com, arnd@arndb.de, kblaiech@mellanox.com, jarkko.nikula@linux.intel.com, Sergey.Semin@baikalelectronics.ru, rppt@kernel.org, loic.poulain@linaro.org, tali.perry1@gmail.com, u.kleine-koenig@pengutronix.de, bjorn.andersson@linaro.org, yu1.wang@intel.com, shuo.a.liu@intel.com, stefanha@redhat.com, pbonzini@redhat.com References: <226a8d5663b7bb6f5d06ede7701eedb18d1bafa1.1616493817.git.jie.deng@intel.com> <20210323090108.ygx76exdgzudeeqi@vireshk-i7> <20210323093839.n7cq7f5poebqdwit@vireshk-i7> <5a415dbe-8e3b-2731-cc52-19aeadda1a17@intel.com> <20210324035225.skkllxexjl65gs6x@vireshk-i7> From: Jie Deng Message-ID: <70a2d0f7-ac48-b477-8368-7ef55696bff1@intel.com> Date: Wed, 24 Mar 2021 12:00:33 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Firefox/78.0 Thunderbird/78.7.0 MIME-Version: 1.0 In-Reply-To: <20210324035225.skkllxexjl65gs6x@vireshk-i7> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Precedence: bulk List-ID: X-Mailing-List: linux-i2c@vger.kernel.org On 2021/3/24 11:52, Viresh Kumar wrote: > On 24-03-21, 08:53, Jie Deng wrote: >> On 2021/3/23 17:38, Viresh Kumar wrote: >>> On 23-03-21, 14:31, Viresh Kumar wrote: >>>> On 23-03-21, 22:19, Jie Deng wrote: >>>>> +static int virtio_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num) >>>>> +{ >>>>> + struct virtio_i2c *vi = i2c_get_adapdata(adap); >>>>> + struct virtqueue *vq = vi->vq; >>>>> + struct virtio_i2c_req *reqs; >>>>> + unsigned long time_left; >>>>> + int ret, nr; >>>>> + >>>>> + reqs = kcalloc(num, sizeof(*reqs), GFP_KERNEL); >>>>> + if (!reqs) >>>>> + return -ENOMEM; >>>>> + >>>>> + mutex_lock(&vi->lock); >>>>> + >>>>> + ret = virtio_i2c_send_reqs(vq, reqs, msgs, num); >>>>> + if (ret == 0) >>>>> + goto err_unlock_free; >>>>> + >>>>> + nr = ret; >>>>> + reinit_completion(&vi->completion); >>>> I think I may have found a possible bug here. This reinit_completion() must >>>> happen before we call virtio_i2c_send_reqs(). It is certainly possible (surely >>>> in corner cases) that virtio_i2c_msg_done() may get called right after >>>> virtio_i2c_send_reqs() and before we were able to call reinit_completion(). And >>>> in that case we will never see the completion happen at all. >>>> >>>>> + virtqueue_kick(vq); >>> I may have misread this. Can the actually start before virtqueue_kick() is >>> called ? > I didn't write it properly here. I wanted to say, > > "Can the _transfer_ actually start before virtqueue_kick() is called ?" > It can't start until the virtqueue_kick() is called. Call virtqueue_kick then wait.