From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-2.mimecast.com ([205.139.110.61]:20947 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726081AbfJUGAG (ORCPT ); Mon, 21 Oct 2019 02:00:06 -0400 Subject: Re: [PATCH V4 5/6] virtio: introduce a mdev based transport References: <20191017104836.32464-1-jasowang@redhat.com> <20191017104836.32464-6-jasowang@redhat.com> <20191018162007.31631039.cohuck@redhat.com> From: Jason Wang Message-ID: <2bb5645b-5c46-9cae-0571-65c302f51cf2@redhat.com> Date: Mon, 21 Oct 2019 13:59:23 +0800 MIME-Version: 1.0 In-Reply-To: <20191018162007.31631039.cohuck@redhat.com> Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: quoted-printable Sender: linux-s390-owner@vger.kernel.org List-ID: To: Cornelia Huck Cc: kvm@vger.kernel.org, linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, intel-gfx@lists.freedesktop.org, intel-gvt-dev@lists.freedesktop.org, kwankhede@nvidia.com, alex.williamson@redhat.com, mst@redhat.com, tiwei.bie@intel.com, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, maxime.coquelin@redhat.com, cunming.liang@intel.com, zhihong.wang@intel.com, rob.miller@broadcom.com, xiao.w.wang@intel.com, haotian.wang@sifive.com, zhenyuw@linux.intel.com, zhi.a.wang@intel.com, jani.nikula@linux.intel.com, joonas.lahtinen@linux.intel.com, rodrigo.vivi@intel.com, airlied@linux.ie, daniel@ffwll.ch, farman@linux.ibm.com, pasic@linux.ibm.com, sebott@linux.ibm.com, oberpar@linux.ibm.com, heiko.carstens@de.ibm.com, gor@linux.ibm.com, borntraeger@de.ibm.com, akrowiak@linux.ibm.com, freude@linux.ibm.com, lingshan.zhu@intel.com, idos@mellanox.com, eperezma@redhat.com, lulu@redhat.com, parav@mellanox.com, christophe.de.dinechin@gmail.com, kevin.tian@intel.com, stefanha@redhat.com On 2019/10/18 =E4=B8=8B=E5=8D=8810:20, Cornelia Huck wrote: > On Thu, 17 Oct 2019 18:48:35 +0800 > Jason Wang wrote: > >> This patch introduces a new mdev transport for virtio. This is used to >> use kernel virtio driver to drive the mediated device that is capable >> of populating virtqueue directly. >> >> A new virtio-mdev driver will be registered to the mdev bus, when a >> new virtio-mdev device is probed, it will register the device with >> mdev based config ops. This means it is a software transport between >> mdev driver and mdev device. The transport was implemented through >> device specific ops which is a part of mdev_parent_ops now. >> >> Signed-off-by: Jason Wang >> --- >> drivers/virtio/Kconfig | 7 + >> drivers/virtio/Makefile | 1 + >> drivers/virtio/virtio_mdev.c | 409 +++++++++++++++++++++++++++++++++++ >> 3 files changed, 417 insertions(+) > (...) > >> +static int virtio_mdev_probe(struct device *dev) >> +{ >> +=09struct mdev_device *mdev =3D mdev_from_dev(dev); >> +=09const struct virtio_mdev_device_ops *ops =3D mdev_get_dev_ops(mdev); >> +=09struct virtio_mdev_device *vm_dev; >> +=09int rc; >> + >> +=09vm_dev =3D devm_kzalloc(dev, sizeof(*vm_dev), GFP_KERNEL); >> +=09if (!vm_dev) >> +=09=09return -ENOMEM; >> + >> +=09vm_dev->vdev.dev.parent =3D dev; >> +=09vm_dev->vdev.dev.release =3D virtio_mdev_release_dev; >> +=09vm_dev->vdev.config =3D &virtio_mdev_config_ops; >> +=09vm_dev->mdev =3D mdev; >> +=09INIT_LIST_HEAD(&vm_dev->virtqueues); >> +=09spin_lock_init(&vm_dev->lock); >> + >> +=09vm_dev->version =3D ops->get_mdev_features(mdev); >> +=09if (vm_dev->version !=3D VIRTIO_MDEV_F_VERSION_1) { >> +=09=09dev_err(dev, "VIRTIO_MDEV_F_VERSION_1 is mandatory\n"); >> +=09=09return -ENXIO; >> +=09} > Hm, so how is that mdev features interface supposed to work? If > VIRTIO_MDEV_F_VERSION_1 is a bit, I would expect this code to test for > its presence, and not for identity. This should be used by driver to detect the which sets of functions and=20 their semantics that could be provided by the device. E.g when driver=20 support both version 2 and version 1 but device only support version 1,=20 driver can switch to use version 1. Btw, Is there a easy way for to test=20 its presence or do you mean doing sanity testing on existence of the=20 mandatory ops that provided by the device? > > What will happen if we come up with a version 2? If this is backwards > compatible, will both version 2 and version 1 be set? Yes, I think so, and version 2 should be considered as some extensions=20 of version 1. If it's completely, it should use a new class id. Thanks > >> + >> +=09vm_dev->vdev.id.device =3D ops->get_device_id(mdev); >> +=09if (vm_dev->vdev.id.device =3D=3D 0) >> +=09=09return -ENODEV; >> + >> +=09vm_dev->vdev.id.vendor =3D ops->get_vendor_id(mdev); >> +=09rc =3D register_virtio_device(&vm_dev->vdev); >> +=09if (rc) >> +=09=09put_device(dev); >> +=09else >> +=09=09dev_set_drvdata(dev, vm_dev); >> + >> +=09return rc; >> +} > (...)