net: lan743x: permit VLAN-tagged packets up to configured MTU

VLAN-tagged interfaces on lan743x devices were previously unreachable via
SSH and failed to respond to large ping packets (e.g. "ping -s 1469" given
MTU=1500). In these scenarios, "ethtool -S" reports non-zero "RX Oversize
Frame Errors". According to Microchip AN2948, the MAC_RX FSE (VLAN field
size enforcement) bit determines whether frames with VLAN tags exceeding
the base MTU plus tag length are discarded.

The driver must set the MAC_RX.FSE bit before setting MAC_RX.RXEN to allow
VLAN-tagged frames up to the interface MTU, preventing them from being
treated as oversized. As a result, both the base and VLAN-tagged interfaces
can use the same MTU without receive errors.

Fixes: 23f0703c125b ("lan743x: Add main source files for new lan743x driver")
Signed-off-by: David Thompson <davthompson@nvidia.com>
Reviewed-by: Thangaraj Samynathan <Thangaraj.s@microchip.com>
Reviewed-by: Nicolai Buchwitz <nb@tipi-net.de>
Tested-by: Nicolai Buchwitz <nb@tipi-net.de> # lan7430 on arm64 (RevPi
Link: https://patch.msgid.link/20260529210300.433135-1-davthompson@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/drivers/net/ethernet/microchip/lan743x_main.c b/drivers/net/ethernet/microchip/lan743x_main.c
index f3332417162e65d3fa0aab10a072a34242af6a40..ffac22883e497199b7c8a0566f20acfc79fa430e 100644 (file)
--- a/drivers/net/ethernet/microchip/lan743x_main.c
+++ b/drivers/net/ethernet/microchip/lan743x_main.c
@@ -1219,6 +1219,36 @@ static void lan743x_mac_set_address(struct lan743x_adapter *adapter,
                   "MAC address set to %pM\n", addr);
 }
 
+static void lan743x_mac_rx_enable_fse(struct lan743x_adapter *adapter)
+{
+       u32 mac_rx;
+       bool rxen;
+
+       mac_rx = lan743x_csr_read(adapter, MAC_RX);
+       if (mac_rx & MAC_RX_FSE_)
+               return;
+
+       rxen = mac_rx & MAC_RX_RXEN_;
+       if (rxen) {
+               mac_rx &= ~MAC_RX_RXEN_;
+               lan743x_csr_write(adapter, MAC_RX, mac_rx);
+               lan743x_csr_wait_for_bit(adapter, MAC_RX, MAC_RX_RXD_,
+                                        1, 1000, 20000, 100);
+       }
+
+       /* Per AN2948, hardware prevents modification of the FSE bit while the
+        * MAC receiver is enabled (RXEN bit set). Use separate register write
+        * to assert the FSE bit before enabling the RXEN bit in MAC_RX
+        */
+       mac_rx |= MAC_RX_FSE_;
+       lan743x_csr_write(adapter, MAC_RX, mac_rx);
+
+       if (rxen) {
+               mac_rx |= MAC_RX_RXEN_;
+               lan743x_csr_write(adapter, MAC_RX, mac_rx);
+       }
+}
+
 static int lan743x_mac_init(struct lan743x_adapter *adapter)
 {
        bool mac_address_valid = true;
@@ -1258,6 +1288,8 @@ static int lan743x_mac_init(struct lan743x_adapter *adapter)
        lan743x_mac_set_address(adapter, adapter->mac_address);
        eth_hw_addr_set(netdev, adapter->mac_address);
 
+       lan743x_mac_rx_enable_fse(adapter);
+
        return 0;
 }
 

diff --git a/drivers/net/ethernet/microchip/lan743x_main.h b/drivers/net/ethernet/microchip/lan743x_main.h
index 160d94a7cee66a45affadcdf1d58a445e3baaea4..1573c8f9c99370a6e1b454c6aea8d555b39915af 100644 (file)
--- a/drivers/net/ethernet/microchip/lan743x_main.h
+++ b/drivers/net/ethernet/microchip/lan743x_main.h
@@ -182,6 +182,7 @@
 #define MAC_RX                         (0x104)
 #define MAC_RX_MAX_SIZE_SHIFT_         (16)
 #define MAC_RX_MAX_SIZE_MASK_          (0x3FFF0000)
+#define MAC_RX_FSE_                    BIT(2)
 #define MAC_RX_RXD_                    BIT(1)
 #define MAC_RX_RXEN_                   BIT(0)