virtio-pci-modern: introduce vp_modern_generation()

This patch introduces vp_modern_generation() to get device generation.
Signed-off-by: Jason Wang <jasowang@redhat.com>
Link: https://lore.kernel.org/r/20210104065503.199631-9-jasowang@redhat.comSigned-off-by: Michael S. Tsirkin <mst@redhat.com>

drivers/virtio/virtio_pci_modern.c

@@ -289,15 +289,26 @@ static void vp_set(struct virtio_device *vdev, unsigned offset,
 	}
 }
 
-static u32 vp_generation(struct virtio_device *vdev)
+/*
+ * vp_modern_generation - get the device genreation
+ * @mdev: the modern virtio-pci device
+ *
+ * Returns the genreation read from device
+ */
+static u32 vp_modern_generation(struct virtio_pci_modern_device *mdev)
 {
-	struct virtio_pci_device *vp_dev = to_vp_device(vdev);
-	struct virtio_pci_modern_device *mdev = &vp_dev->mdev;
 	struct virtio_pci_common_cfg __iomem *cfg = mdev->common;
 
 	return vp_ioread8(&cfg->config_generation);
 }
 
+static u32 vp_generation(struct virtio_device *vdev)
+{
+	struct virtio_pci_device *vp_dev = to_vp_device(vdev);
+
+	return vp_modern_generation(&vp_dev->mdev);
+}
+
 /*
  * vp_modern_get_status - get the device status
  * @mdev: the modern virtio-pci device