[PATCH AUTOSEL 6.17-6.1] net/mlx5e: Don't query FEC statistics when FEC is disabled

[Sasha Levin <sashal@kernel.org>]

From: Carolina Jubran <cjubran@nvidia.com>

[ Upstream commit 6b81b8a0b1978284e007566d7a1607b47f92209f ]

Update mlx5e_stats_fec_get() to check the active FEC mode and skip
statistics collection when FEC is disabled.

Signed-off-by: Carolina Jubran <cjubran@nvidia.com>
Reviewed-by: Dragos Tatulea <dtatulea@nvidia.com>
Reviewed-by: Yael Chemla <ychemla@nvidia.com>
Signed-off-by: Vadim Fedorenko <vadim.fedorenko@linux.dev>
Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>
Link: https://patch.msgid.link/20250924124037.1508846-3-vadim.fedorenko@linux.dev
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

LLM Generated explanations, may be completely bogus:

YES
- `drivers/net/ethernet/mellanox/mlx5/core/en_stats.c:1611` now checks
  `mode == MLX5E_FEC_NOFEC` before touching the PPCNT register groups,
  so the driver stops trying to read FEC statistics when hardware
  reports that FEC is disabled. Previously `mlx5e_stats_fec_get()` still
  called `fec_set_corrected_bits_total()` even in that state, so every
  FEC stats query attempted an unsupported PPCNT access.
- Those reads go through `mlx5_core_access_reg()` with `verbose=true`
  (`drivers/net/ethernet/mellanox/mlx5/core/port.c:36-83`), which means
  firmware failures get logged and waste command bandwidth. Admins hit
  this whenever tools poll FEC stats on links running without FEC, so it
  is a user-visible bug.
- Passing the already computed `mode` into `fec_set_block_stats()`
  (`drivers/net/ethernet/mellanox/mlx5/core/en_stats.c:1448-1471` and
  `:1616`) keeps the existing per-mode handling while avoiding redundant
  `fec_active_mode()` calls; no other callers are affected, so the
  change stays self-contained.
- The patch introduces no new features or interfaces—it simply avoids
  querying counters that do not exist in the “no FEC” configuration—so
  it satisfies stable rules (clear bug fix, minimal risk, contained to
  the mlx5e stats code) and should be backported.

 drivers/net/ethernet/mellanox/mlx5/core/en_stats.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_stats.c b/drivers/net/ethernet/mellanox/mlx5/core/en_stats.c
index c6185ddba04b8..9c45c6e670ebf 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en_stats.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en_stats.c
@@ -1446,16 +1446,13 @@ static void fec_set_rs_stats(struct ethtool_fec_stats *fec_stats, u32 *ppcnt)
 }
 
 static void fec_set_block_stats(struct mlx5e_priv *priv,
+				int mode,
 				struct ethtool_fec_stats *fec_stats)
 {
 	struct mlx5_core_dev *mdev = priv->mdev;
 	u32 out[MLX5_ST_SZ_DW(ppcnt_reg)] = {};
 	u32 in[MLX5_ST_SZ_DW(ppcnt_reg)] = {};
 	int sz = MLX5_ST_SZ_BYTES(ppcnt_reg);
-	int mode = fec_active_mode(mdev);
-
-	if (mode == MLX5E_FEC_NOFEC)
-		return;
 
 	MLX5_SET(ppcnt_reg, in, local_port, 1);
 	MLX5_SET(ppcnt_reg, in, grp, MLX5_PHYSICAL_LAYER_COUNTERS_GROUP);
@@ -1497,11 +1494,14 @@ static void fec_set_corrected_bits_total(struct mlx5e_priv *priv,
 void mlx5e_stats_fec_get(struct mlx5e_priv *priv,
 			 struct ethtool_fec_stats *fec_stats)
 {
-	if (!MLX5_CAP_PCAM_FEATURE(priv->mdev, ppcnt_statistical_group))
+	int mode = fec_active_mode(priv->mdev);
+
+	if (mode == MLX5E_FEC_NOFEC ||
+	    !MLX5_CAP_PCAM_FEATURE(priv->mdev, ppcnt_statistical_group))
 		return;
 
 	fec_set_corrected_bits_total(priv, fec_stats);
-	fec_set_block_stats(priv, fec_stats);
+	fec_set_block_stats(priv, mode, fec_stats);
 }
 
 #define PPORT_ETH_EXT_OFF(c) \
-- 
2.51.0