[PATCH] virtio: support VIRTIO_F_ORDER_PLATFORM

[Tiwei Bie]

This patch introduces the support for VIRTIO_F_ORDER_PLATFORM.
When this feature is negotiated, driver will use the barriers
suitable for hardware devices.

Signed-off-by: Tiwei Bie <tiwei.bie@xxxxxxxxx>
---
 drivers/virtio/virtio_ring.c       | 8 ++++++++
 include/uapi/linux/virtio_config.h | 6 ++++++
 2 files changed, 14 insertions(+)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index cd7e755484e3..27d3f057493e 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -1609,6 +1609,9 @@ static struct virtqueue *vring_create_virtqueue_packed(
 		!context;
 	vq->event = virtio_has_feature(vdev, VIRTIO_RING_F_EVENT_IDX);
 
+	if (virtio_has_feature(vdev, VIRTIO_F_ORDER_PLATFORM))
+		vq->weak_barriers = false;
+
 	vq->packed.ring_dma_addr = ring_dma_addr;
 	vq->packed.driver_event_dma_addr = driver_event_dma_addr;
 	vq->packed.device_event_dma_addr = device_event_dma_addr;
@@ -2079,6 +2082,9 @@ struct virtqueue *__vring_new_virtqueue(unsigned int index,
 		!context;
 	vq->event = virtio_has_feature(vdev, VIRTIO_RING_F_EVENT_IDX);
 
+	if (virtio_has_feature(vdev, VIRTIO_F_ORDER_PLATFORM))
+		vq->weak_barriers = false;
+
 	vq->split.queue_dma_addr = 0;
 	vq->split.queue_size_in_bytes = 0;
 
@@ -2213,6 +2219,8 @@ void vring_transport_features(struct virtio_device *vdev)
 			break;
 		case VIRTIO_F_RING_PACKED:
 			break;
+		case VIRTIO_F_ORDER_PLATFORM:
+			break;
 		default:
 			/* We don't understand this bit. */
 			__virtio_clear_bit(vdev, i);
diff --git a/include/uapi/linux/virtio_config.h b/include/uapi/linux/virtio_config.h
index 1196e1c1d4f6..ff8e7dc9d4dd 100644
--- a/include/uapi/linux/virtio_config.h
+++ b/include/uapi/linux/virtio_config.h
@@ -78,6 +78,12 @@
 /* This feature indicates support for the packed virtqueue layout. */
 #define VIRTIO_F_RING_PACKED		34
 
+/*
+ * This feature indicates that memory accesses by the driver and the
+ * device are ordered in a way described by the platform.
+ */
+#define VIRTIO_F_ORDER_PLATFORM		36
+
 /*
  * Does the device support Single Root I/O Virtualization?
  */
-- 
2.17.1