[RFC PATCH] vdpa: mandate 1.0 device

[Jason Wang <jasowang@redhat.com>]

This patch mandates 1.0 for vDPA devices. The goal is to have the
semantic of normative statement in the virtio spec and eliminate the
burden of transitional device for both vDPA bus and vDPA parent.

uAPI seems fine since all the vDPA parent mandates
VIRTIO_F_ACCESS_PLATFORM which implies 1.0 devices.

For legacy guests, it can still work since Qemu will mediate when
necessary (e.g doing the endian conversion).

Signed-off-by: Jason Wang <jasowang@redhat.com>
---
 include/linux/vdpa.h | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/include/linux/vdpa.h b/include/linux/vdpa.h
index 0fefeb976877..cfde4ec999b4 100644
--- a/include/linux/vdpa.h
+++ b/include/linux/vdpa.h
@@ -6,6 +6,7 @@
 #include <linux/device.h>
 #include <linux/interrupt.h>
 #include <linux/vhost_iotlb.h>
+#include <uapi/linux/virtio_config.h>
 
 /**
  * vDPA callback definition.
@@ -317,6 +318,11 @@ static inline int vdpa_set_features(struct vdpa_device *vdev, u64 features)
 {
         const struct vdpa_config_ops *ops = vdev->config;
 
+        /* Mandating 1.0 to have semantics of normative statements in
+         * the spec. */
+        if (!(features & BIT_ULL(VIRTIO_F_VERSION_1)))
+		return -EINVAL;
+
 	vdev->features_valid = true;
         return ops->set_features(vdev, features);
 }
-- 
2.25.1