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=-10.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 C0CAEC07E99 for ; Tue, 6 Jul 2021 01:50:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A169861977 for ; Tue, 6 Jul 2021 01:50:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229760AbhGFBxI (ORCPT ); Mon, 5 Jul 2021 21:53:08 -0400 Received: from mga17.intel.com ([192.55.52.151]:33050 "EHLO mga17.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229733AbhGFBxH (ORCPT ); Mon, 5 Jul 2021 21:53:07 -0400 X-IronPort-AV: E=McAfee;i="6200,9189,10036"; a="189418844" X-IronPort-AV: E=Sophos;i="5.83,327,1616482800"; d="scan'208";a="189418844" Received: from fmsmga001.fm.intel.com ([10.253.24.23]) by fmsmga107.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 05 Jul 2021 18:50:29 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.83,327,1616482800"; d="scan'208";a="562831796" Received: from dengjie-mobl1.ccr.corp.intel.com (HELO [10.239.154.58]) ([10.239.154.58]) by fmsmga001.fm.intel.com with ESMTP; 05 Jul 2021 18:50:24 -0700 Subject: Re: [PATCH v10] i2c: virtio: add a virtio i2c frontend driver To: Viresh Kumar , Wolfram Sang , linux-i2c@vger.kernel.org, virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org, mst@redhat.com, jasowang@redhat.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> <20210629101627.kwc2rszborc3kvjs@vireshk-i7> <20210629103014.nlk3mpetydc4mi6l@vireshk-i7> <20210705121832.fmye5xnlbydoc5ir@vireshk-i7> From: Jie Deng Message-ID: <29f27ee2-5a65-f635-0b0a-d35d7c4839fb@intel.com> Date: Tue, 6 Jul 2021 09:50:23 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Firefox/78.0 Thunderbird/78.10.0 MIME-Version: 1.0 In-Reply-To: <20210705121832.fmye5xnlbydoc5ir@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 2021/7/5 20:18, Viresh Kumar wrote: > On 29-06-21, 12:43, Wolfram Sang wrote: >>> From the spec: >>> >>> The case when ``length of \field{write_buf}''=0, and at the same time, >>> ``length of \field{read_buf}''=0 doesn't make any sense. >>> >>> I mentioned this in my first reply and to my understanding I did not get >>> a reply that this has changed meanwhile. >>> >> Also, this code as mentioned before: >> >>> + if (!msgs[i].len) >>> + break; >> I hope this can extended in the future to allow zero-length messages. If >> this is impossible we need to set an adapter quirk instead. > Wolfram, > > I stumbled again upon this while working at the backend implementation. > > If you look at i2c_smbus_xfer_emulated(), the command is always sent via > msgbuf0[0]. Even in the case of I2C_SMBUS_QUICK, where we set msg[0].len = 0, we > still send the buf. This is really confusing :( > > Do I understand correctly that we always need to send msg[0].buf even when > msg[0].len is 0 ? > > If so, it would be difficult to implement this with the current i2c virtio > specification, as the msg.len isn't really passed from guest to host, rather it > is inferred using the length of the buffer itself. And so we can't really pass a > buffer if length is 0. > > Moreover, the driver uses i2c_get_dma_safe_msg_buf(), which also depends on the > length parameter here to allocate the buffer and copy data to it. > > All in all, the latest version of the driver doesn't work with "i2cdetect -q ". > > To make it work, I had to add this: > > diff --git a/drivers/i2c/busses/i2c-virtio.c b/drivers/i2c/busses/i2c-virtio.c > index 731267d42292..5b8bd98ae38e 100644 > --- a/drivers/i2c/busses/i2c-virtio.c > +++ b/drivers/i2c/busses/i2c-virtio.c > @@ -73,6 +73,9 @@ static int virtio_i2c_prepare_reqs(struct virtqueue *vq, > sg_init_one(&out_hdr, &reqs[i].out_hdr, sizeof(reqs[i].out_hdr)); > sgs[outcnt++] = &out_hdr; > > + if (!msgs[i].len) > + msgs[i].len = 1; > + > if (msgs[i].len) { > reqs[i].buf = i2c_get_dma_safe_msg_buf(&msgs[i], 1); > if (!reqs[i].buf) > > which made it I2C_SMBUS_BYTE instead of I2C_SMBUS_QUICK. > > What should we do here Wolfram? > > > Jie, while wolfram comes back and replies to this, I think you need to switch > back to NOT supporting zero length transfer and set update virtio_i2c_func() to > return: > > I2C_FUNC_I2C | (I2C_FUNC_SMBUS_EMUL & ~I2C_FUNC_SMBUS_QUICK); > > Support for zero-length transfers and I2C_FUNC_SMBUS_QUICK can be added > separately. > > Thanks. It's OK to me. Let's see what Wolfram says when he comes back. I will send the updated version then. Thanks.