[dpdk-dev] [PATCH v2 1/3] virtio: fix the vq size issue

[Stephen Hemminger <stephen@networkplumber.org>]

From: Ouyang Changchun <changchun.ouyang@intel.com>

This commit breaks virtio basic packets rx functionality:
  d78deadae4dca240e85054bf2d604a801676becc

The QEMU use 256 as default vring size, also use this default value to
calculate the virtio avail ring base address and used ring base
address, and vhost in the backend use the ring base address to do
packet IO.

Virtio spec also says the queue size in PCI configuration is
read-only, so virtio front end can't change it. just need use the
read-only value to allocate space for vring and calculate the avail
and used ring base address. Otherwise, the avail and used ring base
address will be different between host and guest, accordingly, packet
IO can't work normally.

Signed-off-by: Changchun Ouyang <changchun.ouyang@intel.com>
Acked-by: Stephen Hemminger <stephen@networkplumber.org>
---
 drivers/net/virtio/virtio_ethdev.c | 14 +++-----------
 1 file changed, 3 insertions(+), 11 deletions(-)

diff --git a/drivers/net/virtio/virtio_ethdev.c b/drivers/net/virtio/virtio_ethdev.c
index 9ca9bb2..94b7a81 100644
--- a/drivers/net/virtio/virtio_ethdev.c
+++ b/drivers/net/virtio/virtio_ethdev.c
@@ -276,8 +276,6 @@ int virtio_dev_queue_setup(struct rte_eth_dev *dev,
 	 */
 	vq_size = VIRTIO_READ_REG_2(hw, VIRTIO_PCI_QUEUE_NUM);
 	PMD_INIT_LOG(DEBUG, "vq_size: %d nb_desc:%d", vq_size, nb_desc);
-	if (nb_desc == 0)
-		nb_desc = vq_size;
 	if (vq_size == 0) {
 		PMD_INIT_LOG(ERR, "%s: virtqueue does not exist", __func__);
 		return -EINVAL;
@@ -288,15 +286,9 @@ int virtio_dev_queue_setup(struct rte_eth_dev *dev,
 		return -EINVAL;
 	}
 
-	if (nb_desc < vq_size) {
-		if (!rte_is_power_of_2(nb_desc)) {
-			PMD_INIT_LOG(ERR,
-				     "nb_desc(%u) size is not powerof 2",
-				     nb_desc);
-			return -EINVAL;
-		}
-		vq_size = nb_desc;
-	}
+	if (nb_desc != vq_size)
+		PMD_INIT_LOG(ERR, "Warning: nb_desc(%d) is not equal to vq size (%d), fall to vq size",
+			nb_desc, vq_size);
 
 	if (queue_type == VTNET_RQ) {
 		snprintf(vq_name, sizeof(vq_name), "port%d_rvq%d",
-- 
2.1.4