net/mlx5e: Introduce lost_cqe statistic counter for PTP Tx port timestamping CQ

Track the number of times a CQE was expected to not be delivered on PTP Tx
port timestamping CQ. A CQE is expected to not be delivered if a certain
amount of time passes since the corresponding CQE containing the DMA
timestamp information has arrived. Increment the late_cqe counter when such
a CQE does manage to be delivered to the CQ.

Signed-off-by: Rahul Rameshbabu <rrameshbabu@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Reviewed-by: Dragos Tatulea <dtatulea@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>
Link: https://lore.kernel.org/r/20240403212931.128541-3-rrameshbabu@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Documentation/networking/device_drivers/ethernet/mellanox/mlx5/counters.rst

@@ -702,6 +702,12 @@ the software port.
        the device typically ensures not posting the CQE.
      - Error
 
+   * - `ptp_cq[i]_lost_cqe`
+     - Number of times a CQE is expected to not be delivered on the PTP
+       timestamping CQE by the device due to a time delta elapsing. If such a
+       CQE is somehow delivered, `ptp_cq[i]_late_cqe` is incremented.
+     - Error
+
 .. [#ring_global] The corresponding ring and global counters do not share the
                   same name (i.e. do not follow the common naming scheme).
 

drivers/net/ethernet/mellanox/mlx5/core/en/ptp.c

@@ -169,6 +169,7 @@ static void mlx5e_ptpsq_mark_ts_cqes_undelivered(struct mlx5e_ptpsq *ptpsq,
 		WARN_ON_ONCE(!pos->inuse);
 		pos->inuse = false;
 		list_del(&pos->entry);
+		ptpsq->cq_stats->lost_cqe++;
 	}
 	spin_unlock_bh(&cqe_list->tracker_list_lock);
 }

drivers/net/ethernet/mellanox/mlx5/core/en_stats.c

@@ -2178,6 +2178,7 @@ static const struct counter_desc ptp_cq_stats_desc[] = {
 	{ MLX5E_DECLARE_PTP_CQ_STAT(struct mlx5e_ptp_cq_stats, abort) },
 	{ MLX5E_DECLARE_PTP_CQ_STAT(struct mlx5e_ptp_cq_stats, abort_abs_diff_ns) },
 	{ MLX5E_DECLARE_PTP_CQ_STAT(struct mlx5e_ptp_cq_stats, late_cqe) },
+	{ MLX5E_DECLARE_PTP_CQ_STAT(struct mlx5e_ptp_cq_stats, lost_cqe) },
 };
 
 static const struct counter_desc ptp_rq_stats_desc[] = {

drivers/net/ethernet/mellanox/mlx5/core/en_stats.h

@@ -463,6 +463,7 @@ struct mlx5e_ptp_cq_stats {
 	u64 abort;
 	u64 abort_abs_diff_ns;
 	u64 late_cqe;
+	u64 lost_cqe;
 };
 
 struct mlx5e_rep_stats {