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From:   Alvaro Karsz <alvaro.karsz@solid-run.com>
To:     Viktor Prutyanov <viktor@daynix.com>,
        "mst@redhat.com" <mst@redhat.com>,
        "jasowang@redhat.com" <jasowang@redhat.com>
CC:     "cohuck@redhat.com" <cohuck@redhat.com>,
        "pasic@linux.ibm.com" <pasic@linux.ibm.com>,
        "farman@linux.ibm.com" <farman@linux.ibm.com>,
        "linux-s390@vger.kernel.org" <linux-s390@vger.kernel.org>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        "virtualization@lists.linux-foundation.org" 
        <virtualization@lists.linux-foundation.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "yan@daynix.com" <yan@daynix.com>
Subject: Re: [PATCH v6] virtio: add VIRTIO_F_NOTIFICATION_DATA feature support
Thread-Topic: [PATCH v6] virtio: add VIRTIO_F_NOTIFICATION_DATA feature
 support
Thread-Index: AQHZXon0whv8NnC6hUW1jNhoqDcu6a8W1qQo
Date:   Sun, 2 Apr 2023 08:17:49 +0000
Message-ID: <AM0PR04MB4723A8D079076FA56AB45845D48C9@AM0PR04MB4723.eurprd04.prod.outlook.com>
References: <20230324195029.2410503-1-viktor@daynix.com>
In-Reply-To: <20230324195029.2410503-1-viktor@daynix.com>
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Hi Viktor,=0A=
=0A=
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c=
=0A=
> index 4c3bb0ddeb9b..f9c6604352b4 100644=0A=
> --- a/drivers/virtio/virtio_ring.c=0A=
> +++ b/drivers/virtio/virtio_ring.c=0A=
> @@ -2752,6 +2752,23 @@ void vring_del_virtqueue(struct virtqueue *_vq)=0A=
>  }=0A=
>  EXPORT_SYMBOL_GPL(vring_del_virtqueue);=0A=
> =0A=
> +u32 vring_notification_data(struct virtqueue *_vq)=0A=
> +{=0A=
> +       struct vring_virtqueue *vq =3D to_vvq(_vq);=0A=
> +       u16 next;=0A=
> +=0A=
> +       if (vq->packed_ring)=0A=
> +               next =3D (vq->packed.next_avail_idx &=0A=
> +                               ~(-(1 << VRING_PACKED_EVENT_F_WRAP_CTR)))=
 |=0A=
> +                       vq->packed.avail_wrap_counter <<=0A=
> +                               VRING_PACKED_EVENT_F_WRAP_CTR;=0A=
> +       else=0A=
> +               next =3D vq->split.avail_idx_shadow;=0A=
> +=0A=
> +       return next << 16 | _vq->index;=0A=
> +}=0A=
> +EXPORT_SYMBOL_GPL(vring_notification_data);=0A=
> +=0A=
>  /* Manipulates transport-specific feature bits. */=0A=
>  void vring_transport_features(struct virtio_device *vdev)=0A=
>  {=0A=
> @@ -2771,6 +2788,8 @@ void vring_transport_features(struct virtio_device =
*vdev)=0A=
>                         break;=0A=
>                 case VIRTIO_F_ORDER_PLATFORM:=0A=
>                         break;=0A=
> +               case VIRTIO_F_NOTIFICATION_DATA:=0A=
> +                       break;=0A=
=0A=
This function is used by virtio_vdpa as well (drivers/virtio/virtio_vdpa.c:=
virtio_vdpa_finalize_features).=0A=
A vDPA device can offer this feature and it will be accepted, even though V=
IRTIO_F_NOTIFICATION_DATA is not a thing for the vDPA transport at the mome=
nt.=0A=
=0A=
I don't know if this is bad, since offering VIRTIO_F_NOTIFICATION_DATA is m=
eaningless for a vDPA device at the moment.=0A=
=0A=
I submitted a patch adding support for vDPA transport.=0A=
https://lore.kernel.org/virtualization/20230402081034.1021886-1-alvaro.kars=
z@solid-run.com/T/#u=0A=
=0A=
>                 default:=0A=
>                         /* We don't understand this bit. */=0A=
>                         __virtio_clear_bit(vdev, i);=0A=