[dpdk-dev] [PATCH] virtio: fix the vq size issue

[Ouyang Changchun]

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 at intel.com>
---
 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 fe5f9a1..d84de13 100644
--- a/drivers/net/virtio/virtio_ethdev.c
+++ b/drivers/net/virtio/virtio_ethdev.c
@@ -263,8 +263,6 @@ 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;
@@ -275,15 +273,9 @@ 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",
-- 
1.8.4.2