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,URIBL_BLOCKED,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 C42F1C433E0 for ; Tue, 16 Mar 2021 02:16:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9173665014 for ; Tue, 16 Mar 2021 02:16:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234516AbhCPCQY (ORCPT ); Mon, 15 Mar 2021 22:16:24 -0400 Received: from mga06.intel.com ([134.134.136.31]:26012 "EHLO mga06.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230080AbhCPCPz (ORCPT ); Mon, 15 Mar 2021 22:15:55 -0400 IronPort-SDR: g/oOyX9GElpCtkKe1HaS/o7G3xOnkHEChrM/Lf3N0/fKAQhqSg/MVTx9xYbE/UC7Ac/vPGcvY7 n9Dbm1MIMVaQ== X-IronPort-AV: E=McAfee;i="6000,8403,9924"; a="250550829" X-IronPort-AV: E=Sophos;i="5.81,251,1610438400"; d="scan'208";a="250550829" Received: from fmsmga004.fm.intel.com ([10.253.24.48]) by orsmga104.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 15 Mar 2021 19:15:54 -0700 IronPort-SDR: oTD9KtMZ1jjPn6HxxlOF7zsOZemh5Z32NM5g4Up6ZSwF7Ji3sjGKsLHH8syDq4M9M9HH0NvotD zELrdGYi2vyQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.81,251,1610438400"; d="scan'208";a="432855368" Received: from unknown (HELO [10.239.154.55]) ([10.239.154.55]) by fmsmga004.fm.intel.com with ESMTP; 15 Mar 2021 19:15:49 -0700 Subject: Re: [PATCH v7] i2c: virtio: add a virtio i2c frontend driver To: Arnd Bergmann Cc: Jason Wang , Linux I2C , virtualization@lists.linux-foundation.org, "linux-kernel@vger.kernel.org" , "Michael S. Tsirkin" , Wolfram Sang , Wolfram Sang , Andy Shevchenko , conghui.chen@intel.com, kblaiech@mellanox.com, jarkko.nikula@linux.intel.com, Sergey Semin , Mike Rapoport , loic.poulain@linaro.org, Tali Perry , =?UTF-8?Q?Uwe_Kleine-K=c3=b6nig?= , Bjorn Andersson , yu1.wang@intel.com, shuo.a.liu@intel.com, Viresh Kumar , Stefan Hajnoczi , Paolo Bonzini References: <8070f03d-8233-636b-5ea9-395e723f7a2c@intel.com> <503b88c9-1e82-a3a3-0536-d710ddc834a5@redhat.com> From: Jie Deng Message-ID: <770332a7-f34d-fe26-f708-830b587a98d5@intel.com> Date: Tue, 16 Mar 2021 10:15:48 +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: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US Precedence: bulk List-ID: X-Mailing-List: linux-i2c@vger.kernel.org On 2021/3/15 15:52, Arnd Bergmann wrote: > On Mon, Mar 15, 2021 at 6:54 AM Jie Deng wrote: >> On 2021/3/15 11:13, Jason Wang wrote: >>> On 2021/3/15 9:14 上午, Jie Deng wrote: >>>> On 2021/3/12 16:58, Arnd Bergmann wrote: >> Then do you think it is necessary to mark the virtio bufs with >> ____cacheline_aligned ? > I think so, yes. > >> I haven't seen any virtio interface being marked yet. If this is a >> problem, I believe it should be common for all virtio devices, right ? > Yes, but it's not a problem if the buffers are allocated separately > because kmalloc provinces a cachelinen aligned buffer on architectures > that need it. > > It's only a problem here because there is a single allocation for three > objects that have different ownership states during the DMA (device > owned to-device, cpu-owned, device owned to-cpu). > > Arnd I'm not sure if this will actually cause a problem. But I'm OK to mark the items in struct virtio_i2c_req with  ____cacheline_aligned to avoid potential problem as you said. Thank you.