net/mlx5e: Add stale counter for PCIe congestion events

This ethtool counter is meant to help with observing how many times the
congestion event was triggered but on query there was no state change.

This would help to indicate when a work item was scheduled to run too
late and in the meantime the congestion state changed back to previous
state.

While at it, do a driveby typo fix in documentation for
pci_bw_inbound_high.

Signed-off-by: Dragos Tatulea <[email protected]>
Signed-off-by: Tariq Toukan <[email protected]>
Reviewed-by: Simon Horman <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

Author: dtatulea

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

@@ -1348,7 +1348,7 @@ Device Counters
        is in a congested state.
        If pci_bw_inbound_high == pci_bw_inbound_low then the device is not congested.
        If pci_bw_inbound_high > pci_bw_inbound_low then the device is congested.
-     - Tnformative
+     - Informative
 
    * - `pci_bw_inbound_low`
      - The number of times the device crossed the low inbound PCIe bandwidth
@@ -1373,3 +1373,8 @@ Device Counters
        If pci_bw_outbound_high == pci_bw_outbound_low then the device is not congested.
        If pci_bw_outbound_high > pci_bw_outbound_low then the device is congested.
      - Informative
+
+   * - `pci_bw_stale_event`
+     - The number of times the device fired a PCIe congestion event but on query
+       there was no change in state.
+     - Informative

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

@@ -24,6 +24,7 @@ struct mlx5e_pcie_cong_stats {
 	u32 pci_bw_inbound_low;
 	u32 pci_bw_outbound_high;
 	u32 pci_bw_outbound_low;
+	u32 pci_bw_stale_event;
 };
 
 struct mlx5e_pcie_cong_event {
@@ -52,6 +53,8 @@ static const struct counter_desc mlx5e_pcie_cong_stats_desc[] = {
 			     pci_bw_outbound_high) },
 	{ MLX5E_DECLARE_STAT(struct mlx5e_pcie_cong_stats,
 			     pci_bw_outbound_low) },
+	{ MLX5E_DECLARE_STAT(struct mlx5e_pcie_cong_stats,
+			     pci_bw_stale_event) },
 };
 
 #define NUM_PCIE_CONG_COUNTERS ARRAY_SIZE(mlx5e_pcie_cong_stats_desc)
@@ -212,8 +215,10 @@ static void mlx5e_pcie_cong_event_work(struct work_struct *work)
 	}
 
 	changes = cong_event->state ^ new_cong_state;
-	if (!changes)
+	if (!changes) {
+		cong_event->stats.pci_bw_stale_event++;
 		return;
+	}
 
 	cong_event->state = new_cong_state;