net/ixgbe: fix TDH register write

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: 029fd06d40fa ("ixgbe: queue start and stop")
Cc: stable@dpdk.org
Signed-off-by: Yanglong Wu <yanglong.wu@intel.com>
Acked-by: Qi Zhang <qi.z.zhang@intel.com>

diff --git a/drivers/net/ixgbe/ixgbe_rxtx.c b/drivers/net/ixgbe/ixgbe_rxtx.c
index 2f0262a..ddc7efa 100644 (file)
--- 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;