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=-2.3 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,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 D61E9C43215 for ; Fri, 22 Nov 2019 09:14:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id AEB9820714 for ; Fri, 22 Nov 2019 09:14:31 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="QlcZToBA" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726526AbfKVJOa (ORCPT ); Fri, 22 Nov 2019 04:14:30 -0500 Received: from us-smtp-2.mimecast.com ([207.211.31.81]:32543 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726100AbfKVJOa (ORCPT ); Fri, 22 Nov 2019 04:14:30 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1574414068; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=iWuR/xiXoJz8XNdtmPyrzUwrAACjqWWaKc7K3C9SBjw=; b=QlcZToBA0hMWew0V/naJ3lnf4b652NcUmHbxE/xHxsLAVGi66JG2ru9wqOM/TBtI6DW0vw oziJg9yeFAH9CiGiFtLUHLkKwNZzPCQjcK36LV+qjZe9KwneLEKnmYKgG0hafcrCPCBkJg xWUNCNT6ONeTOrr9W0mMinLrVDrPPEY= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-393-U4pLxVscM8eEdnkBROBTpw-1; Fri, 22 Nov 2019 04:14:25 -0500 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id F3E5D107ACC4; Fri, 22 Nov 2019 09:14:22 +0000 (UTC) Received: from [10.72.13.3] (ovpn-13-3.pek2.redhat.com [10.72.13.3]) by smtp.corp.redhat.com (Postfix) with ESMTP id D743326FC4; Fri, 22 Nov 2019 09:13:59 +0000 (UTC) Subject: Re: [net-next v2 1/1] virtual-bus: Implementation of Virtual Bus To: Martin Habets , Parav Pandit , Jeff Kirsher , "davem@davemloft.net" , "gregkh@linuxfoundation.org" Cc: Dave Ertman , "netdev@vger.kernel.org" , "linux-rdma@vger.kernel.org" , "nhorman@redhat.com" , "sassmann@redhat.com" , "jgg@ziepe.ca" , Kiran Patil , "Michael S. Tsirkin" , Alex Williamson , "Bie, Tiwei" References: <20191115223355.1277139-1-jeffrey.t.kirsher@intel.com> <30b968cf-0e11-a2c6-5b9f-5518df11dfb7@solarflare.com> From: Jason Wang Message-ID: <22dd6ae3-03f4-1432-2935-8df5e9a449de@redhat.com> Date: Fri, 22 Nov 2019 17:13:56 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <30b968cf-0e11-a2c6-5b9f-5518df11dfb7@solarflare.com> Content-Language: en-US X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-MC-Unique: U4pLxVscM8eEdnkBROBTpw-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: quoted-printable Sender: linux-rdma-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-rdma@vger.kernel.org On 2019/11/21 =E4=B8=8B=E5=8D=8811:10, Martin Habets wrote: > On 19/11/2019 04:08, Jason Wang wrote: >> On 2019/11/16 =E4=B8=8A=E5=8D=887:25, Parav Pandit wrote: >>> Hi Jeff, >>> >>>> From: Jeff Kirsher >>>> Sent: Friday, November 15, 2019 4:34 PM >>>> >>>> From: Dave Ertman >>>> >>>> This is the initial implementation of the Virtual Bus, virtbus_device = and >>>> virtbus_driver.=C2=A0 The virtual bus is a software based bus intended= to support >>>> lightweight devices and drivers and provide matching between them and >>>> probing of the registered drivers. >>>> >>>> The primary purpose of the virual bus is to provide matching services = and to >>>> pass the data pointer contained in the virtbus_device to the virtbus_d= river >>>> during its probe call.=C2=A0 This will allow two separate kernel objec= ts to match up >>>> and start communication. >>>> >>> It is fundamental to know that rdma device created by virtbus_driver wi= ll be anchored to which bus for an non abusive use. >>> virtbus or parent pci bus? >>> I asked this question in v1 version of this patch. >>> >>> Also since it says - 'to support lightweight devices', documenting that= information is critical to avoid ambiguity. >>> >>> Since for a while I am working on the subbus/subdev_bus/xbus/mdev [1] w= hatever we want to call it, it overlaps with your comment about 'to support= lightweight devices'. >>> Hence let's make things crystal clear weather the purpose is 'only matc= hing service' or also 'lightweight devices'. >>> If this is only matching service, lets please remove lightweight device= s part.. >> >> Yes, if it's matching + lightweight device, its function is almost a dup= lication of mdev. And I'm working on extending mdev[1] to be a generic modu= le to support any types of virtual devices a while. The advantage of mdev i= s: >> >> 1) ready for the userspace driver (VFIO based) >> 2) have a sysfs/GUID based management interface > In my view this virtual-bus is more generic and more flexible than mdev. Even after the series [1] here? > What for you are the advantages of mdev to me are some of it's disadvanta= ges. > > The way I see it we can provide rdma support in the driver using virtual-= bus. Yes, but since it does matching only, you can do everything you want.=20 But it looks to me Greg does not want a bus to be an API multiplexer. So=20 if a dedicated bus is desired, it won't be much of code to have a bus on=20 your own. > At the moment we would need separate mdev support in the driver for vdpa,= but I hope at some point mdev > would become a layer on top of virtual-bus. > Besides these users we also support internal tools for our hardware facto= ry provisioning, and for testing/debugging. > I could easily imagine such tools using a virtual-bus device. With mdev t= hose interfaces would be more convoluted. Can you give me an example? > >> So for 1, it's not clear that how userspace driver would be supported he= re, or it's completely not being accounted in this series? For 2, it looks = to me that this series leave it to the implementation, this means managemen= t to learn several vendor specific interfaces which seems a burden. >> >> Note, technically Virtual Bus could be implemented on top of [1] with th= e full lifecycle API. > Seems easier to me to do that the other way around: mdev could be impleme= nted on top of virtual-bus. Probably, without the part of parent_ops, they are almost equal. Thanks > > Best regards, > Martin > >> [1] https://lkml.org/lkml/2019/11/18/261 >> >> >>> You additionally need modpost support for id table integration to modif= o, modprobe and other tools. >>> A small patch similar to this one [2] is needed. >>> Please include in the series. >>> >>> [..] >> >> And probably a uevent method. But rethinking of this, matching through a= single virtual bus seems not good. What if driver want to do some specific= matching? E.g for virtio, we may want a vhost-net driver that only match n= etworking device. With a single bus, it probably means you need another bus= on top and provide the virtio specific matching there. This looks not stra= ightforward as allowing multiple type of buses. >> >> Thanks >>