netdev - Re: [PATCH RESEND net-next v2 2/5] net: thunderbolt: Allow changing MTU of the device

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Message-ID: <b070f4f6-e81b-4674-954b-609ad17f1cda@blackwall.org>
Date: Fri, 9 Jan 2026 14:35:41 +0200
From: Nikolay Aleksandrov <razor@...ckwall.org>
To: Mika Westerberg <mika.westerberg@...ux.intel.com>, netdev@...r.kernel.org
Cc: Yehezkel Bernat <YehezkelShB@...il.com>, Ian MacDonald
 <ian@...statz.com>, Salvatore Bonaccorso <carnil@...ian.org>,
 Andrew Lunn <andrew+netdev@...n.ch>, "David S . Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 Jay Vosburgh <jv@...sburgh.net>, Simon Horman <horms@...nel.org>
Subject: Re: [PATCH RESEND net-next v2 2/5] net: thunderbolt: Allow changing
 MTU of the device

On 09/01/2026 14:26, Mika Westerberg wrote:
> In some cases it is useful to be able to use different MTU than the
> default one. Especially when dealing against non-Linux networking stack.
> For this reason add possibility to change the MTU of the device.
> 
> Signed-off-by: Mika Westerberg <mika.westerberg@...ux.intel.com>
> ---
>   drivers/net/thunderbolt/main.c | 11 +++++++++++
>   1 file changed, 11 insertions(+)
> 
> diff --git a/drivers/net/thunderbolt/main.c b/drivers/net/thunderbolt/main.c
> index 57b226afeb84..20bac55a3e20 100644
> --- a/drivers/net/thunderbolt/main.c
> +++ b/drivers/net/thunderbolt/main.c
> @@ -1257,12 +1257,23 @@ static void tbnet_get_stats64(struct net_device *dev,
>   	stats->rx_missed_errors = net->stats.rx_missed_errors;
>   }
>   
> +static int tbnet_change_mtu(struct net_device *dev, int new_mtu)
> +{
> +	/* Keep the MTU within supported range */
> +	if (new_mtu < 68 || new_mtu > (TBNET_MAX_MTU - ETH_HLEN))
> +		return -EINVAL;
> +
> +	dev->mtu = new_mtu;
> +	return 0;
> +}
> +
>   static const struct net_device_ops tbnet_netdev_ops = {
>   	.ndo_open = tbnet_open,
>   	.ndo_stop = tbnet_stop,
>   	.ndo_start_xmit = tbnet_start_xmit,
>   	.ndo_set_mac_address = eth_mac_addr,
>   	.ndo_get_stats64 = tbnet_get_stats64,
> +	.ndo_change_mtu	= tbnet_change_mtu,
>   };
>   
>   static void tbnet_generate_mac(struct net_device *dev)

You can use struct net_device's min/max_mtu instead of a custom 
ndo_change_mtu.
They will be validated by dev_validate_mtu().

Cheers,
  Nik