RE: [PATCH v2 net-next 4/5] net: fec: add change_mtu to support dynamic buffer allocation

[Wei Fang]

> +static int fec_change_mtu(struct net_device *ndev, int new_mtu)
> +{
> +	struct fec_enet_private *fep = netdev_priv(ndev);
> +	int order, done;
> +	bool running;
> +
> +	order = get_order(new_mtu + ETH_HLEN + ETH_FCS_LEN);
> +	if (fep->pagepool_order == order) {
> +		WRITE_ONCE(ndev->mtu, new_mtu);
> +		return 0;
> +	}
> +
> +	fep->pagepool_order = order;
> +	fep->rx_frame_size = (PAGE_SIZE << order) - FEC_ENET_XDP_HEADROOM
> +			     - SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
> +

I think we need to add a check for rx_frame_size, as FEC_R_CNTRL[MAX_FL]
and FEC_FTRL[TRUNC_FL] only have 14 bits.