mlxsw: core_env: Fix driver initialization with old firmware

The driver queries the Management Capabilities Mask (MCAM) register
during initialization to understand if it can read up to 128 bytes from
transceiver modules.

However, not all firmware versions support this register, leading to the
driver failing to load.

Fix by treating an error in the register query as an indication that the
feature is not supported.

Fixes: 1f4aea1 ("mlxsw: core_env: Read transceiver module EEPROM in 128 bytes chunks")
Reported-by: Tim 'mithro' Ansell <[email protected]>
Signed-off-by: Ido Schimmel <[email protected]>
Reviewed-by: Petr Machata <[email protected]>
Signed-off-by: Petr Machata <[email protected]>
Reviewed-by: Simon Horman <[email protected]>
Link: https://lore.kernel.org/r/0afa8b2e8bac178f5f88211344429176dcc72281.1713446092.git.petrm@nvidia.com
Signed-off-by: Jakub Kicinski <[email protected]>

Author: idosch

drivers/net/ethernet/mellanox/mlxsw/core_env.c

@@ -1357,24 +1357,20 @@ static struct mlxsw_linecards_event_ops mlxsw_env_event_ops = {
 	.got_inactive = mlxsw_env_got_inactive,
 };
 
-static int mlxsw_env_max_module_eeprom_len_query(struct mlxsw_env *mlxsw_env)
+static void mlxsw_env_max_module_eeprom_len_query(struct mlxsw_env *mlxsw_env)
 {
 	char mcam_pl[MLXSW_REG_MCAM_LEN];
-	bool mcia_128b_supported;
+	bool mcia_128b_supported = false;
 	int err;
 
 	mlxsw_reg_mcam_pack(mcam_pl,
 			    MLXSW_REG_MCAM_FEATURE_GROUP_ENHANCED_FEATURES);
 	err = mlxsw_reg_query(mlxsw_env->core, MLXSW_REG(mcam), mcam_pl);
-	if (err)
-		return err;
-
-	mlxsw_reg_mcam_unpack(mcam_pl, MLXSW_REG_MCAM_MCIA_128B,
-			      &mcia_128b_supported);
+	if (!err)
+		mlxsw_reg_mcam_unpack(mcam_pl, MLXSW_REG_MCAM_MCIA_128B,
+				      &mcia_128b_supported);
 
 	mlxsw_env->max_eeprom_len = mcia_128b_supported ? 128 : 48;
-
-	return 0;
 }
 
 int mlxsw_env_init(struct mlxsw_core *mlxsw_core,
@@ -1445,15 +1441,11 @@ int mlxsw_env_init(struct mlxsw_core *mlxsw_core,
 	if (err)
 		goto err_type_set;
 
-	err = mlxsw_env_max_module_eeprom_len_query(env);
-	if (err)
-		goto err_eeprom_len_query;
-
+	mlxsw_env_max_module_eeprom_len_query(env);
 	env->line_cards[0]->active = true;
 
 	return 0;
 
-err_eeprom_len_query:
 err_type_set:
 	mlxsw_env_module_event_disable(env, 0);
 err_mlxsw_env_module_event_enable: