net/mlx4: fix premature disabling of interrupt

RXQ interrupts under Linux are based on the epoll mechanism. An
expected order of operations is as follows:
1. Call rte_eth_dev_rx_intr_enable(), to arm the CQ for receiving events
on data input.
2. Block on rte_epoll_wait() with an array of file descriptors
representing the CQ events. Upon data arrival the kernel will signal an
input event on the corresponding CQ fd.
3. Call rte_eth_dev_rx_intr_disable() after the event was received and
continue in polling mode. The mlx4 implementation of
rte_eth_dev_rx_intr_disable() is to get the CQ event and ack it.

In practice applications may wake up from rte_epoll_wait() due to
timeout with no event to ack but still call
rte_eth_dev_rx_intr_disable() unconditionally.  In such cases the call
should return EAGAIN (since the file descriptors are non-blocked), as
opposed to EINVAL which indicates a real failure.  In case of EAGAIN the
PMD should not warn on "unable to disable interrupt on rx queue".

Signed-off-by: Ophir Munk <ophirmu@mellanox.com>
Acked-by: Raslan Darawsheh <rasland@mellanox.com>

diff --git a/drivers/net/mlx4/mlx4_intr.c b/drivers/net/mlx4/mlx4_intr.c
index 020fc25..19af935 100644 (file)
--- a/drivers/net/mlx4/mlx4_intr.c
+++ b/drivers/net/mlx4/mlx4_intr.c
@@ -326,13 +326,20 @@ mlx4_rx_intr_disable(struct rte_eth_dev *dev, uint16_t idx)
        } else {
                ret = mlx4_glue->get_cq_event(rxq->cq->channel, &ev_cq,
                                              &ev_ctx);
-               if (ret || ev_cq != rxq->cq)
+               /** For non-zero ret save the errno (may be EAGAIN
+                * which means the get_cq_event function was called before
+                * receiving one).
+                */
+               if (ret)
+                       ret = errno;
+               else if (ev_cq != rxq->cq)
                        ret = EINVAL;
        }
        if (ret) {
                rte_errno = ret;
-               WARN("unable to disable interrupt on rx queue %d",
-                    idx);
+               if (ret != EAGAIN)
+                       WARN("unable to disable interrupt on rx queue %d",
+                            idx);
        } else {
                rxq->mcq.arm_sn++;
                mlx4_glue->ack_cq_events(rxq->cq, 1);