[dpdk-dev] [PATCH] net/ixgbe: fix TDH register setting issue

[Yanglong Wu]

The only time that software should write to the TDH register
is after a reset (hardware reset or CTRL.RST) and
before enabling the transmit function (TXDCTL.ENABLE).
If software were to write to this register while the transmit
function was enabled, the on-chip descriptor buffers might
be invalidated and the hardware could become confused.

Fixes: a8cdaf0964f7 ("net/ixgbe: remove redundant queue id checks")
Signed-off-by: Yanglong Wu <yanglong.wu at intel.com>
---
 drivers/net/ixgbe/ixgbe_rxtx.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ixgbe/ixgbe_rxtx.c b/drivers/net/ixgbe/ixgbe_rxtx.c
index 2f0262ae1..ddc7efa87 100644
--- a/drivers/net/ixgbe/ixgbe_rxtx.c
+++ b/drivers/net/ixgbe/ixgbe_rxtx.c
@@ -5264,6 +5264,7 @@ ixgbe_dev_tx_queue_start(struct rte_eth_dev *dev, uint16_t tx_queue_id)
 	hw = IXGBE_DEV_PRIVATE_TO_HW(dev->data->dev_private);
 
 	txq = dev->data->tx_queues[tx_queue_id];
+	IXGBE_WRITE_REG(hw, IXGBE_TDH(txq->reg_idx), 0);
 	txdctl = IXGBE_READ_REG(hw, IXGBE_TXDCTL(txq->reg_idx));
 	txdctl |= IXGBE_TXDCTL_ENABLE;
 	IXGBE_WRITE_REG(hw, IXGBE_TXDCTL(txq->reg_idx), txdctl);
@@ -5281,7 +5282,6 @@ ixgbe_dev_tx_queue_start(struct rte_eth_dev *dev, uint16_t tx_queue_id)
 				tx_queue_id);
 	}
 	rte_wmb();
-	IXGBE_WRITE_REG(hw, IXGBE_TDH(txq->reg_idx), 0);
 	IXGBE_WRITE_REG(hw, IXGBE_TDT(txq->reg_idx), 0);
 	dev->data->tx_queue_state[tx_queue_id] = RTE_ETH_QUEUE_STATE_STARTED;
 
-- 
2.11.0