--- /dev/null
+From 6599df775e2cbb4988bdf8239acf4fbec70e5ef9 Mon Sep 17 00:00:00 2001
+From: Linus Walleij <linus.walleij@linaro.org>
+Date: Sat, 23 Sep 2023 20:38:22 +0200
+Subject: [PATCH 3/4] net: ixp4xx_eth: Support changing the MTU
+
+As we don't specify the MTU in the driver, the framework
+will fall back to 1500 bytes and this doesn't work very
+well when we try to attach a DSA switch:
+
+ eth1: mtu greater than device maximum
+ ixp4xx_eth c800a000.ethernet eth1: error -22 setting
+ MTU to 1504 to include DSA overhead
+
+After locating an out-of-tree patch in OpenWrt I found
+suitable code to set the MTU on the interface and ported
+it and updated it. Now the MTU gets set properly.
+
+Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
+Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
+---
+ drivers/net/ethernet/xscale/ixp4xx_eth.c | 65 +++++++++++++++++++++++-
+ 1 file changed, 64 insertions(+), 1 deletion(-)
+
+--- a/drivers/net/ethernet/xscale/ixp4xx_eth.c
++++ b/drivers/net/ethernet/xscale/ixp4xx_eth.c
+@@ -24,6 +24,7 @@
+ #include <linux/dma-mapping.h>
+ #include <linux/dmapool.h>
+ #include <linux/etherdevice.h>
++#include <linux/if_vlan.h>
+ #include <linux/io.h>
+ #include <linux/kernel.h>
+ #include <linux/net_tstamp.h>
+@@ -63,7 +64,15 @@
+
+ #define POOL_ALLOC_SIZE (sizeof(struct desc) * (RX_DESCS + TX_DESCS))
+ #define REGS_SIZE 0x1000
+-#define MAX_MRU 1536 /* 0x600 */
++
++/* MRU is said to be 14320 in a code dump, the SW manual says that
++ * MRU/MTU is 16320 and includes VLAN and ethernet headers.
++ * See "IXP400 Software Programmer's Guide" section 10.3.2, page 161.
++ *
++ * FIXME: we have chosen the safe default (14320) but if you can test
++ * jumboframes, experiment with 16320 and see what happens!
++ */
++#define MAX_MRU (14320 - VLAN_ETH_HLEN)
+ #define RX_BUFF_SIZE ALIGN((NET_IP_ALIGN) + MAX_MRU, 4)
+
+ #define NAPI_WEIGHT 16
+@@ -1182,6 +1191,54 @@ static void destroy_queues(struct port *
+ }
+ }
+
++static int ixp4xx_do_change_mtu(struct net_device *dev, int new_mtu)
++{
++ struct port *port = netdev_priv(dev);
++ struct npe *npe = port->npe;
++ int framesize, chunks;
++ struct msg msg = {};
++
++ /* adjust for ethernet headers */
++ framesize = new_mtu + VLAN_ETH_HLEN;
++ /* max rx/tx 64 byte chunks */
++ chunks = DIV_ROUND_UP(framesize, 64);
++
++ msg.cmd = NPE_SETMAXFRAMELENGTHS;
++ msg.eth_id = port->id;
++
++ /* Firmware wants to know buffer size in 64 byte chunks */
++ msg.byte2 = chunks << 8;
++ msg.byte3 = chunks << 8;
++
++ msg.byte4 = msg.byte6 = framesize >> 8;
++ msg.byte5 = msg.byte7 = framesize & 0xff;
++
++ if (npe_send_recv_message(npe, &msg, "ETH_SET_MAX_FRAME_LENGTH"))
++ return -EIO;
++ netdev_dbg(dev, "set MTU on NPE %s to %d bytes\n",
++ npe_name(npe), new_mtu);
++
++ return 0;
++}
++
++static int ixp4xx_eth_change_mtu(struct net_device *dev, int new_mtu)
++{
++ int ret;
++
++ /* MTU can only be changed when the interface is up. We also
++ * set the MTU from dev->mtu when opening the device.
++ */
++ if (dev->flags & IFF_UP) {
++ ret = ixp4xx_do_change_mtu(dev, new_mtu);
++ if (ret < 0)
++ return ret;
++ }
++
++ dev->mtu = new_mtu;
++
++ return 0;
++}
++
+ static int eth_open(struct net_device *dev)
+ {
+ struct port *port = netdev_priv(dev);
+@@ -1232,6 +1289,8 @@ static int eth_open(struct net_device *d
+ if (npe_send_recv_message(port->npe, &msg, "ETH_SET_FIREWALL_MODE"))
+ return -EIO;
+
++ ixp4xx_do_change_mtu(dev, dev->mtu);
++
+ if ((err = request_queues(port)) != 0)
+ return err;
+
+@@ -1374,6 +1433,7 @@ static int eth_close(struct net_device *
+ static const struct net_device_ops ixp4xx_netdev_ops = {
+ .ndo_open = eth_open,
+ .ndo_stop = eth_close,
++ .ndo_change_mtu = ixp4xx_eth_change_mtu,
+ .ndo_start_xmit = eth_xmit,
+ .ndo_set_rx_mode = eth_set_mcast_list,
+ .ndo_eth_ioctl = eth_ioctl,
+@@ -1488,6 +1548,9 @@ static int ixp4xx_eth_probe(struct platf
+ ndev->dev.dma_mask = dev->dma_mask;
+ ndev->dev.coherent_dma_mask = dev->coherent_dma_mask;
+
++ ndev->min_mtu = ETH_MIN_MTU;
++ ndev->max_mtu = MAX_MRU;
++
+ netif_napi_add_weight(ndev, &port->napi, eth_poll, NAPI_WEIGHT);
+
+ if (!(port->npe = npe_request(NPE_ID(port->id))))