mlxsw: pci: Fix driver initialization with old firmware

The driver queries the Management Capabilities Mask (MCAM) register
during initialization to understand if a new and deeper reset flow is
supported.

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: f257c73 ("mlxsw: pci: Add support for new reset flow")
Reported-by: Tim 'mithro' Ansell <me@mith.ro>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Petr Machata <petrm@nvidia.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Reviewed-by: Kalesh AP <kalesh-anakkur.purayil@broadcom.com>
Signed-off-by: Petr Machata <petrm@nvidia.com>
Link: https://lore.kernel.org/r/ee968c49d53bac96a4c66d1b09ebbd097d81aca5.1713446092.git.petrm@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

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

@@ -1530,7 +1530,7 @@ mlxsw_pci_reset(struct mlxsw_pci *mlxsw_pci, const struct pci_device_id *id)
 {
 	struct pci_dev *pdev = mlxsw_pci->pdev;
 	char mcam_pl[MLXSW_REG_MCAM_LEN];
-	bool pci_reset_supported;
+	bool pci_reset_supported = false;
 	u32 sys_status;
 	int err;
 
@@ -1548,11 +1548,9 @@ mlxsw_pci_reset(struct mlxsw_pci *mlxsw_pci, const struct pci_device_id *id)
 	mlxsw_reg_mcam_pack(mcam_pl,
 			    MLXSW_REG_MCAM_FEATURE_GROUP_ENHANCED_FEATURES);
 	err = mlxsw_reg_query(mlxsw_pci->core, MLXSW_REG(mcam), mcam_pl);
-	if (err)
-		return err;
-
-	mlxsw_reg_mcam_unpack(mcam_pl, MLXSW_REG_MCAM_PCI_RESET,
-			      &pci_reset_supported);
+	if (!err)
+		mlxsw_reg_mcam_unpack(mcam_pl, MLXSW_REG_MCAM_PCI_RESET,
+				      &pci_reset_supported);
 
 	if (pci_reset_supported) {
 		pci_dbg(pdev, "Starting PCI reset flow\n");