From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-1.mimecast.com ([207.211.31.81]:32307 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726725AbfJUKNl (ORCPT ); Mon, 21 Oct 2019 06:13:41 -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> <2bb5645b-5c46-9cae-0571-65c302f51cf2@redhat.com> <20191021113607.16b26d9d.cohuck@redhat.com> From: Jason Wang Message-ID: <1aa59fea-cae5-6303-4a94-51493d5748ba@redhat.com> Date: Mon, 21 Oct 2019 18:13:02 +0800 MIME-Version: 1.0 In-Reply-To: <20191021113607.16b26d9d.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 2019/10/21 =E4=B8=8B=E5=8D=885:36, Cornelia Huck wrote: > On Mon, 21 Oct 2019 13:59:23 +0800 > Jason Wang wrote: > >> 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: >>> =20 >>>> 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(+) >>> (...) >>> =20 >>>> +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 >> their semantics that could be provided by the device. E.g when driver >> support both version 2 and version 1 but device only support version 1, >> driver can switch to use version 1. Btw, Is there a easy way for to test >> its presence or do you mean doing sanity testing on existence of the >> mandatory ops that provided by the device? > What I meant was something like: > > features =3D ops->get_mdev_features(mdev); > if (features & VIRTIO_MDEV_F_VERSION_1) > =09vm_dev->version =3D 1; > else > =09//moan about missing support for version 1 > > Can there be class id specific extra features, or is this only for core > features? If the latter, maybe also do something like > > supported_features =3D ORED_LIST_OF_FEATURES; > if (features & ~supported_features) > =09//moan about extra feature bits Consider driver can claim to support a list of ids, so I this it's former. Will do as what you proposed. Thanks > >> >>> 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 >> of version 1. If it's completely, it should use a new class id. > Ok, that makes sense. >