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Tsirkin" , Alex Williamson , "Bie, Tiwei" References: <20191115223355.1277139-1-jeffrey.t.kirsher@intel.com> From: Jason Wang Message-ID: <13946106-dab2-6bbe-df79-ca6dfdeb4c51@redhat.com> Date: Tue, 19 Nov 2019 14:51:29 +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: Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-MC-Unique: zDJqApmwN7KP60fKXZq5hA-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 2019/11/19 =E4=B8=8B=E5=8D=8812:36, Parav Pandit wrote: > Hi Jason Wang, > >> From: Jason Wang >> Sent: Monday, November 18, 2019 10:08 PM >> >> 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. 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_driver during its probe call. This will allow two separate >>>> kernel objects 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] >> whatever we want to call it, it overlaps with your comment about 'to sup= port >> 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 module to >> support any types of virtual devices a while. The advantage of mdev is: >> >> 1) ready for the userspace driver (VFIO based) >> 2) have a sysfs/GUID based management interface >> >> 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 m= e that this >> series leave it to the implementation, this means management to learn se= veral >> vendor specific interfaces which seems a burden. >> >> Note, technically Virtual Bus could be implemented on top of [1] with th= e full >> lifecycle API. >> >> [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 specif= ic >> matching? E.g for virtio, we may want a vhost-net driver that only match >> networking device. With a single bus, it probably means you need another= bus >> on top and provide the virtio specific matching there. >> This looks not straightforward as allowing multiple type of buses. >> > The purpose of the bus is to attach two drivers, Right, I just start to think whether it was generic to support the case=20 as virtio or mdev to avoid function duplications. > mlx5_core (creator of netdevices) and mlx5_ib (create of rdma devices) = on single PCI function. > Meaning 'multiple classes of devices' are created on top of single underl= ying parent device. This is not what I read, the doc said: " +One use case example is an rdma driver needing to connect with several +different types of PCI LAN devices to be able to request resources from +them (queue sets).=C2=A0 Each LAN driver that supports rdma will register = a +virtbus_device on the virtual bus for each physical function. The rdma +driver will register as a virtbus_driver on the virtual bus to be +matched up with multiple virtbus_devices and receive a pointer to a +struct containing the callbacks that the PCI LAN drivers support for +registering with them. " So it means to connect a single rdma driver with several RDMA capable=20 LAN drivers on top of several PCI functions. If this is true, I'm not=20 quite sure the advantage of using a bus since it's more like aggregation=20 as what bond/team did. > > So bus is just the 'matching service' and nothing more. It is not meant t= o address virtio, mdev, sub functions usecases. Probably, for virtio mdev we need more than just matching: life cycle=20 management, cooperation with VFIO and we also want to be prepared for=20 the device slicing (like sub functions). Thanks