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=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 8AE31C4363A for ; Thu, 29 Oct 2020 13:35:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3D30E20809 for ; Thu, 29 Oct 2020 13:35:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727190AbgJ2NfS (ORCPT ); Thu, 29 Oct 2020 09:35:18 -0400 Received: from mga12.intel.com ([192.55.52.136]:20010 "EHLO mga12.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726482AbgJ2NfS (ORCPT ); Thu, 29 Oct 2020 09:35:18 -0400 IronPort-SDR: bpmpPhVGBayGAeS3y0iKZ5Ftri9VWXF1RBT3l6oGB/RDjSnbC167Qmh2c3g7jwLC0JffAsXnDl 9n8el13XQHrA== X-IronPort-AV: E=McAfee;i="6000,8403,9788"; a="147712752" X-IronPort-AV: E=Sophos;i="5.77,430,1596524400"; d="scan'208";a="147712752" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga004.fm.intel.com ([10.253.24.48]) by fmsmga106.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 29 Oct 2020 06:35:12 -0700 IronPort-SDR: 6KqWRgHxOkP1pXZ8FWz1pviQebG2iDeb3+NBxWwkrq352GAjT320g+H7E/Kq0ks+cXaHLmGx2k WqQy163E1vkA== X-IronPort-AV: E=Sophos;i="5.77,430,1596524400"; d="scan'208";a="351449000" Received: from adixit-mobl1.amr.corp.intel.com (HELO adixit-arch.intel.com) ([10.212.42.193]) by fmsmga004-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 29 Oct 2020 06:35:12 -0700 Date: Thu, 29 Oct 2020 06:35:11 -0700 Message-ID: <87mu05f94g.wl-ashutosh.dixit@intel.com> From: "Dixit, Ashutosh" To: Arnd Bergmann Cc: Vincent Whitchurch , Sherry Sun , "Dutt, Sudeep" , dl-linux-imx , "linux-kernel@vger.kernel.org" , "hch@infradead.org" , "kishon@ti.com" , "lorenzo.pieralisi@arm.com" , "gregkh@linuxfoundation.org" Subject: Re: [PATCH V3 2/4] misc: vop: do not allocate and reassign the used ring In-Reply-To: References: <20201023092650.GB29066@infradead.org> <20201027062802.GC207971@kroah.com> <20201027151106.e4skr6dsbwvo4al6@axis.com> <93bd1c60ea4d910489a7592200856eaf8022ced0.camel@intel.com> <20201029100727.trbppgbusd5vogpz@axis.com> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?ISO-8859-4?Q?Goj=F2?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/27.1 (x86_64-pc-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 29 Oct 2020 04:53:09 -0700, Arnd Bergmann wrote: > > On Thu, Oct 29, 2020 at 11:07 AM Vincent Whitchurch > wrote: > > > > On Wed, Oct 28, 2020 at 04:50:36PM +0100, Arnd Bergmann wrote: > > > I think we should try to do something on top of the PCIe endpoint subsystem > > > to make it work across arbitrary combinations of host and device > > > implementations, > > > and provide a superset of what the MIC driver, (out-of-tree) Bluefield endpoint > > > driver, and the NTB subsystem as well as a couple of others used to do, > > > each of them tunneling block/network/serial/... over a PCIe link of some > > > sort, usually with virtio. > > > > VOP is not PCIe-specific (as demonstrated by the vop-loopback patches I > > posted a while ago [1]), and it would be a shame for a replacement to be > > tied to the PCIe endpoint subsystem. There are many SOCs out there > > which have multiple Linux-capable processors without cache-coherency > > between them. VOP is (or should I say was since I guess it's being > > deleted) the closest we have in mainline to easily get generic virtio > > (and not just rpmsg) running between these kind of Linux instances. If > > a new replacement framework were to be PCIe-exclusive then we'd have to > > invent one more framework for non-PCIe links to do pretty much the same > > thing. > > > > [1] https://lore.kernel.org/lkml/20190403104746.16063-1-vincent.whitchurch@axis.com/ > > Right, sorry I forgot about that. I think this means we should keep having > an abstraction between VOP (under whichever name) and the lower levels, > and be aware that it might run on any number of these: > > - PCIe endpoint, with the endpoint controlling the virtio configuration > - PCIe endpoint, with the host (the side that has the pci_driver) controlling > the virtio configuration > - NTB connections > - your loopback mode > - Virtio tunnels between VM guests (see https://www.linaro.org/projects/#STR) > - Intel MIC (to be removed, but it would be wrong to make assumptions that > cannot be made on that type of hardware) A virtio interface being one between host and guest is inherently asymmetric. The whole innovation of the VOP design was to treat Linux on a PCIe device as a guest, there was even talk at some point of the "guest" being managed via libvirt. So here host and guest retain their specific role/personality. The host "inserts" devices which appear in the guest e.g. So I am not sure how this asymmetry plays in the scenarios mentioned above.