net/mlx5e: Fix setting RS FEC after remapping

When a user sets a FEC mode via ethtool, the driver maps the ethtool
FEC type to the lowest mlx5 bit of that type. For RS FEC, this is
MLX5E_FEC_RS_528_514 (bit 2). The driver then checks whether this
bit is supported by at least one link mode by inspecting the
fec_override_cap fields via mlx5e_fec_in_caps(), and returns
-EOPNOTSUPP if not.

This check is incorrect. RS FEC has three supported hardware variants:
RS_528_514 (bit 2), RS_544_514_INTERLEAVED_QUAD (bit 4), and
RS_544_514 (bit 7). mlx5e_remap_fec_conf_mode() already remaps bit 2
to the appropriate RS variant per link mode when writing the admin
fields, but the early capability check is done against the raw
unmapped bit. As a result, a device that supports RS_544_514 or
RS_544_514_INTERLEAVED_QUAD but not RS_528_514 will incorrectly reject
the user's RS FEC request.

Remove the early support check from mlx5e_set_fec_mode() and fold
it into the existing write loop, checking caps against the remapped
policy per link mode. Return -EOPNOTSUPP before the final register
write if no link mode accepted the policy.

Fixes: 2608a2f831c4 ("net/mlx5e: Fix return status when setting unsupported FEC mode")
Signed-off-by: Shahar Shitrit <shshitrit@nvidia.com>
Reviewed-by: Dragos Tatulea <dtatulea@nvidia.com>
Reviewed-by: Yael Chemla <ychemla@nvidia.com>
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Link: https://patch.msgid.link/20260902164634.3657606-3-tariqt@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 9 insertions, 6 deletions

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en/port.c b/drivers/net/ethernet/mellanox/mlx5/core/en/port.c
index 6049ccf475bc..a4c096a4fed2 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en/port.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en/port.c
@@ -557,6 +557,7 @@ int mlx5e_set_fec_mode(struct mlx5_core_dev *dev, u16 fec_policy)
 	u32 in[MLX5_ST_SZ_DW(pplm_reg)] = {};
 	int sz = MLX5_ST_SZ_BYTES(pplm_reg);
 	u16 fec_policy_auto = 0;
+	bool fec_set = false;
 	int err;
 	int i;
 
@@ -569,9 +570,6 @@ int mlx5e_set_fec_mode(struct mlx5_core_dev *dev, u16 fec_policy)
 	if (fec_policy >= (1 << MLX5E_FEC_LLRS_272_257_1) && !fec_50g_per_lane)
 		return -EOPNOTSUPP;
 
-	if (fec_policy && !mlx5e_fec_in_caps(dev, fec_policy))
-		return -EOPNOTSUPP;
-
 	MLX5_SET(pplm_reg, in, local_port, 1);
 	err = mlx5_core_access_reg(dev, in, sz, out, sz, MLX5_REG_PPLM, 0, 0);
 	if (err)
@@ -591,12 +589,17 @@ int mlx5e_set_fec_mode(struct mlx5_core_dev *dev, u16 fec_policy)
 		mlx5e_get_fec_cap_field(out, &fec_caps, i);
 
 		/* policy supported for link speed */
-		if (fec_caps & conf_fec)
+		if (fec_caps & conf_fec) {
 			mlx5e_fec_admin_field(out, &conf_fec, 1, i);
-		else
-			/* set FEC to auto*/
+			fec_set = true;
+		} else {
+			/* set FEC to auto */
 			mlx5e_fec_admin_field(out, &fec_policy_auto, 1, i);
+		}
 	}
 
+	if (fec_policy && !fec_set)
+		return -EOPNOTSUPP;
+
 	return mlx5_core_access_reg(dev, out, sz, out, sz, MLX5_REG_PPLM, 0, 1);
 }