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=-5.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,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 8E37DC63697 for ; Mon, 16 Nov 2020 05:19:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 34B9522370 for ; Mon, 16 Nov 2020 05:19:52 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=ti.com header.i=@ti.com header.b="GYfchMo9" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726035AbgKPFTb (ORCPT ); Mon, 16 Nov 2020 00:19:31 -0500 Received: from fllv0015.ext.ti.com ([198.47.19.141]:56876 "EHLO fllv0015.ext.ti.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725730AbgKPFTa (ORCPT ); Mon, 16 Nov 2020 00:19:30 -0500 Received: from lelv0265.itg.ti.com ([10.180.67.224]) by fllv0015.ext.ti.com (8.15.2/8.15.2) with ESMTP id 0AG5JCok040603; Sun, 15 Nov 2020 23:19:12 -0600 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ti.com; s=ti-com-17Q1; t=1605503952; bh=3oB89CbTYHpl2o9ZDiCY/Ic+iLDClTkUpWMbGhciyBQ=; h=Subject:To:CC:References:From:Date:In-Reply-To; b=GYfchMo9v/DfW6ccVCdckXt4QZKgJrL3G5GMw28kA7JYyz4+K1RKIyv2vPK3lbKr3 ZLOzNKKyuxJCbpJx4GQD2KGQllnePA8bn5omu05e5fUJZ3DmF/xYaSYt6Z7lwzQI5/ 6COYbZey3qpLaDR0yZjxfqZmD5s4S0UJ76Pf1zq8= Received: from DLEE108.ent.ti.com (dlee108.ent.ti.com [157.170.170.38]) by lelv0265.itg.ti.com (8.15.2/8.15.2) with ESMTPS id 0AG5JB5Y049190 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=FAIL); Sun, 15 Nov 2020 23:19:12 -0600 Received: from DLEE114.ent.ti.com (157.170.170.25) by DLEE108.ent.ti.com (157.170.170.38) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P256) id 15.1.1979.3; Sun, 15 Nov 2020 23:19:11 -0600 Received: from lelv0326.itg.ti.com (10.180.67.84) by DLEE114.ent.ti.com (157.170.170.25) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P256) id 15.1.1979.3 via Frontend Transport; Sun, 15 Nov 2020 23:19:11 -0600 Received: from [10.250.235.36] (ileax41-snat.itg.ti.com [10.172.224.153]) by lelv0326.itg.ti.com (8.15.2/8.15.2) with ESMTP id 0AG5J6v5020556; Sun, 15 Nov 2020 23:19:07 -0600 Subject: Re: [PATCH v7 15/18] NTB: Add support for EPF PCI-Express Non-Transparent Bridge To: Arnd Bergmann CC: Sherry Sun , "bhelgaas@google.com" , Jonathan Corbet , "lorenzo.pieralisi@arm.com" , "arnd@arndb.de" , "jdmason@kudzu.us" , "dave.jiang@intel.com" , "allenbh@gmail.com" , "tjoseph@cadence.com" , Rob Herring , "gregkh@linuxfoundation.org" , "linux-pci@vger.kernel.org" , "linux-doc@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-ntb@googlegroups.com" References: <20200930153519.7282-16-kishon@ti.com> <30c8f7a1-baa5-1eb4-d2c2-9a13be896f0f@ti.com> <5a9115c8-322e-ffd4-6274-ae98c375b21d@ti.com> From: Kishon Vijay Abraham I Message-ID: Date: Mon, 16 Nov 2020 10:49:05 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-EXCLAIMER-MD-CONFIG: e1e8a2fd-e40a-4ac6-ac9b-f7e9cc9ee180 Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org Hi Arnd, On 12/11/20 6:54 pm, Arnd Bergmann wrote: > On Tue, Nov 10, 2020 at 4:42 PM Kishon Vijay Abraham I wrote: >> On 10/11/20 8:29 pm, Arnd Bergmann wrote: >>> On Tue, Nov 10, 2020 at 3:20 PM Kishon Vijay Abraham I wrote: >>>> On 10/11/20 7:55 am, Sherry Sun wrote: >>> >>>>> But for VOP, only two boards are needed(one board as host and one board as card) to realize the >>>>> communication between the two systems, so my question is what are the advantages of using NTB? >>>> >>>> NTB is a bridge that facilitates communication between two different >>>> systems. So it by itself will not be source or sink of any data unlike a >>>> normal EP to RP system (or the VOP) which will be source or sink of data. >>>> >>>>> Because I think the architecture of NTB seems more complicated. Many thanks! >>>> >>>> yeah, I think it enables a different use case all together. Consider you >>>> have two x86 HOST PCs (having RP) and they have to be communicate using >>>> PCIe. NTB can be used in such cases for the two x86 PCs to communicate >>>> with each other over PCIe, which wouldn't be possible without NTB. >>> >>> I think for VOP, we should have an abstraction that can work on either NTB >>> or directly on the endpoint framework but provide an interface that then >>> lets you create logical devices the same way. >>> >>> Doing VOP based on NTB plus the new NTB_EPF driver would also >>> work and just move the abstraction somewhere else, but I guess it >>> would complicate setting it up for those users that only care about the >>> simpler endpoint case. >> >> I'm not sure if you've got a chance to look at [1], where I added >> support for RP<->EP system both running Linux, with EP configured using >> Linux EP framework (as well as HOST ports connected to NTB switch, >> patches 20 and 21, that uses the Linux NTB framework) to communicate >> using virtio over PCIe. >> >> The cover-letter [1] shows a picture of the two use cases supported in >> that series. >> >> [1] -> http://lore.kernel.org/r/20200702082143.25259-1-kishon@ti.com > > No, I missed, that, thanks for pointing me to it! > > This looks very promising indeed, I need to read up on the whole > discussion there. I also see your slides at [1] that help do explain some > of it. I have one fundamental question that I can't figure out from > the description, maybe you can help me here: > > How is the configuration managed, taking the EP case as an > example? Your UseCase1 example sounds like the system that owns > the EP hardware is the one that turns the EP into a vhost device, > and creates a vhost-rpmsg device on top, while the RC side would > probe the pci-vhost and then detect a virtio-rpmsg device to talk to. That's correct. Slide no 9 in [1] should give the layering details. > Can it also do the opposite, so you end up with e.g. a virtio-net > device on the EP side and vhost-net on the RC? Unfortunately no. Again referring slide 9 in [1], we only have vhost-pci-epf on the EP side which only creates a "vhost_dev" to deal with vhost side of things. For doing the opposite, we'd need to create virtio-pci-epf for EP side that interacts with core virtio (and also the corresponding vhost back end on PCI host). Thanks Kishon > > Arnd > > [1] https://linuxplumbersconf.org/event/7/contributions/849/attachments/642/1175/Virtio_for_PCIe_RC_EP_NTB.pdf >