i40e: allow toggling loopback mode via ndo_set_features callback

Add support for NETIF_F_LOOPBACK. This feature can be set via:
$ ethtool -K eth0 loopback <on|off>

This sets the MAC Tx->Rx loopback.

This feature is used for the xsk selftests, and might have other uses
too.

Signed-off-by: Tirthendu Sarkar <tirthendu.sarkar@intel.com>
Reviewed-by: Alexander Lobakin <alexandr.lobakin@intel.com>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Tested-by: Magnus Karlsson <magnus.karlsson@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
Link: https://lore.kernel.org/r/20221209185553.2520088-1-anthony.l.nguyen@intel.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/intel/i40e/i40e_adminq_cmd.h

@@ -1795,9 +1795,11 @@ I40E_CHECK_CMD_LENGTH(i40e_aqc_an_advt_reg);
 /* Set Loopback mode (0x0618) */
 struct i40e_aqc_set_lb_mode {
 	__le16	lb_mode;
-#define I40E_AQ_LB_PHY_LOCAL	0x01
-#define I40E_AQ_LB_PHY_REMOTE	0x02
-#define I40E_AQ_LB_MAC_LOCAL	0x04
+#define I40E_LEGACY_LOOPBACK_NVM_VER	0x6000
+#define I40E_AQ_LB_MAC_LOCAL		0x01
+#define I40E_AQ_LB_PHY_LOCAL		0x05
+#define I40E_AQ_LB_PHY_REMOTE		0x06
+#define I40E_AQ_LB_MAC_LOCAL_LEGACY	0x04
 	u8	reserved[14];
 };
 

drivers/net/ethernet/intel/i40e/i40e_common.c

@@ -1830,6 +1830,32 @@ i40e_status i40e_aq_set_phy_int_mask(struct i40e_hw *hw,
 	return status;
 }
 
+/**
+ * i40e_aq_set_mac_loopback
+ * @hw: pointer to the HW struct
+ * @ena_lpbk: Enable or Disable loopback
+ * @cmd_details: pointer to command details structure or NULL
+ *
+ * Enable/disable loopback on a given port
+ */
+i40e_status i40e_aq_set_mac_loopback(struct i40e_hw *hw, bool ena_lpbk,
+				     struct i40e_asq_cmd_details *cmd_details)
+{
+	struct i40e_aq_desc desc;
+	struct i40e_aqc_set_lb_mode *cmd =
+		(struct i40e_aqc_set_lb_mode *)&desc.params.raw;
+
+	i40e_fill_default_direct_cmd_desc(&desc, i40e_aqc_opc_set_lb_modes);
+	if (ena_lpbk) {
+		if (hw->nvm.version <= I40E_LEGACY_LOOPBACK_NVM_VER)
+			cmd->lb_mode = cpu_to_le16(I40E_AQ_LB_MAC_LOCAL_LEGACY);
+		else
+			cmd->lb_mode = cpu_to_le16(I40E_AQ_LB_MAC_LOCAL);
+	}
+
+	return i40e_asq_send_command(hw, &desc, NULL, 0, cmd_details);
+}
+
 /**
  * i40e_aq_set_phy_debug
  * @hw: pointer to the hw struct

drivers/net/ethernet/intel/i40e/i40e_main.c

@@ -12937,6 +12937,29 @@ static void i40e_clear_rss_lut(struct i40e_vsi *vsi)
 	}
 }
 
+/**
+ * i40e_set_loopback - turn on/off loopback mode on underlying PF
+ * @vsi: ptr to VSI
+ * @ena: flag to indicate the on/off setting
+ */
+static int i40e_set_loopback(struct i40e_vsi *vsi, bool ena)
+{
+	bool if_running = netif_running(vsi->netdev) &&
+			  !test_and_set_bit(__I40E_VSI_DOWN, vsi->state);
+	int ret;
+
+	if (if_running)
+		i40e_down(vsi);
+
+	ret = i40e_aq_set_mac_loopback(&vsi->back->hw, ena, NULL);
+	if (ret)
+		netdev_err(vsi->netdev, "Failed to toggle loopback state\n");
+	if (if_running)
+		i40e_up(vsi);
+
+	return ret;
+}
+
 /**
  * i40e_set_features - set the netdev feature flags
  * @netdev: ptr to the netdev being adjusted
@@ -12977,6 +13000,9 @@ static int i40e_set_features(struct net_device *netdev,
 	if (need_reset)
 		i40e_do_reset(pf, I40E_PF_RESET_FLAG, true);
 
+	if ((features ^ netdev->features) & NETIF_F_LOOPBACK)
+		return i40e_set_loopback(vsi, !!(features & NETIF_F_LOOPBACK));
+
 	return 0;
 }
 
@@ -13739,7 +13765,7 @@ static int i40e_config_netdev(struct i40e_vsi *vsi)
 	if (!(pf->flags & I40E_FLAG_MFP_ENABLED))
 		hw_features |= NETIF_F_NTUPLE | NETIF_F_HW_TC;
 
-	netdev->hw_features |= hw_features;
+	netdev->hw_features |= hw_features | NETIF_F_LOOPBACK;
 
 	netdev->features |= hw_features | NETIF_F_HW_VLAN_CTAG_FILTER;
 	netdev->hw_enc_features |= NETIF_F_TSO_MANGLEID;

drivers/net/ethernet/intel/i40e/i40e_prototype.h

@@ -105,6 +105,9 @@ enum i40e_status_code i40e_aq_set_phy_config(struct i40e_hw *hw,
 				struct i40e_asq_cmd_details *cmd_details);
 enum i40e_status_code i40e_set_fc(struct i40e_hw *hw, u8 *aq_failures,
 				  bool atomic_reset);
+i40e_status i40e_aq_set_mac_loopback(struct i40e_hw *hw,
+				     bool ena_lpbk,
+				     struct i40e_asq_cmd_details *cmd_details);
 i40e_status i40e_aq_set_phy_int_mask(struct i40e_hw *hw, u16 mask,
 				     struct i40e_asq_cmd_details *cmd_details);
 i40e_status i40e_aq_clear_pxe_mode(struct i40e_hw *hw,