Toggle GPIO in Netdevice - linux-device-driver

Question

Hy i wanted to toggle a GPIO pin always when i send a package. But I have a weird behafure sometimes my pin gets toggled and sometimes not. I checked my Kernel logs and there is no Information that the pin could not be toggled.
My Ops look like this:
static const struct net_device_ops stmuart_netdev_ops = {
.ndo_init = stmuart_netdev_init,
.ndo_uninit = stmuart_netdev_uninit,
.ndo_open = stmuart_netdev_open,
.ndo_stop = stmuart_netdev_close,
.ndo_start_xmit = stmuart_netdev_xmit,
.ndo_set_mac_address = eth_mac_addr,
.ndo_tx_timeout = stmuart_netdev_tx_timeout,
.ndo_validate_addr = eth_validate_addr,
};
So as far as i know the ndo_start_xmit method is called as soon as i want to send a package. so i only toggle my pin when this method is called. But when i look on my Oscilloscope i can see that the pin is only sometimes toggled.
My method for sending looks like this:
static netdev_tx_t
stmuart_netdev_xmit(struct sk_buff *skb, struct net_device *dev)
{
struct net_device_stats *n_stats = &dev->stats;
struct stmuart *stm = netdev_priv(dev);
u8 pad_len = 0;
int written;
u8 *pos;
spin_lock(&stm->lock);
gpiod_set_value(stm->rts_gpio, 1);
WARN_ON(stm->tx_left);
if (!netif_running(dev)) {
spin_unlock(&stm->lock);
netdev_warn(stm->net_dev, "xmit: iface is down\n");
goto out;
}
pos = stm->tx_buffer;
if (skb->len < STMFRM_MIN_LEN)
pad_len = STMFRM_MIN_LEN - skb->len;
pos += stmfrm_create_header(pos, skb->len + pad_len);
memcpy(pos, skb->data, skb->len);
pos += skb->len;
if (pad_len) {
memset(pos, 0, pad_len);
pos += pad_len;
}
pos += stmfrm_create_footer(pos);
netif_stop_queue(stm->net_dev);
written = serdev_device_write_buf(stm->serdev, stm->tx_buffer,
pos - stm->tx_buffer);
if (written > 0) {
stm->tx_left = (pos - stm->tx_buffer) - written;
stm->tx_head = stm->tx_buffer + written;
n_stats->tx_bytes += written;
}
spin_unlock(&stm->lock);
out:
gpiod_set_value(stm->rts_gpio, 0);
netif_trans_update(dev);
dev_kfree_skb_any(skb);
return NETDEV_TX_OK;
}
So i checked the netdevice.h but there i did not saw another method that gets called when the net device wants to send a package.
It seems to me like always when the netdevice sends a ARP-Request the pin gets not toggled.