virtio-pci-modern: introduce helper to get notification offset

This patch introduces help to get notification offset of modern device.
Signed-off-by: Jason Wang <jasowang@redhat.com>
Link: https://lore.kernel.org/r/20210104065503.199631-15-jasowang@redhat.comSigned-off-by: Michael S. Tsirkin <mst@redhat.com>

drivers/virtio/virtio_pci_modern.c

@@ -303,6 +303,21 @@ static u16 vp_modern_get_num_queues(struct virtio_pci_modern_device *mdev)
 	return vp_ioread16(&mdev->common->num_queues);
 }
 
+/*
+ * vp_modern_get_queue_notify_off - get notification offset for a virtqueue
+ * @mdev: the modern virtio-pci device
+ * @index: the queue index
+ *
+ * Returns the notification offset for a virtqueue
+ */
+static u16 vp_modern_get_queue_notify_off(struct virtio_pci_modern_device *mdev,
+					  u16 index)
+{
+	vp_iowrite16(index, &mdev->common->queue_select);
+
+	return vp_ioread16(&mdev->common->queue_notify_off);
+}
+
 /* virtio config->finalize_features() implementation */
 static int vp_finalize_features(struct virtio_device *vdev)
 {
@@ -516,7 +531,6 @@ static struct virtqueue *setup_vq(struct virtio_pci_device *vp_dev,
 {
 
 	struct virtio_pci_modern_device *mdev = &vp_dev->mdev;
-	struct virtio_pci_common_cfg __iomem *cfg = mdev->common;
 	struct virtqueue *vq;
 	u16 num, off;
 	int err;
@@ -524,9 +538,6 @@ static struct virtqueue *setup_vq(struct virtio_pci_device *vp_dev,
 	if (index >= vp_modern_get_num_queues(mdev))
 		return ERR_PTR(-ENOENT);
 
-	/* Select the queue we're interested in */
-	vp_iowrite16(index, &cfg->queue_select);
-
 	/* Check if queue is either not available or already active. */
 	num = vp_modern_get_queue_size(mdev, index);
 	if (!num || vp_modern_get_queue_enable(mdev, index))
@@ -538,7 +549,7 @@ static struct virtqueue *setup_vq(struct virtio_pci_device *vp_dev,
 	}
 
 	/* get offset of notification word for this vq */
-	off = vp_ioread16(&cfg->queue_notify_off);
+	off = vp_modern_get_queue_notify_off(mdev, index);
 
 	info->msix_vector = msix_vec;