Re: [PATCH 1/5] net: dsa: b53: fix jumbo frame mtu check

[Florian Fainelli]

On 10/4/2024 1:47 AM, Jonas Gorski wrote:
> JMS_MIN_SIZE is the full ethernet frame length, while mtu is just the
> data payload size. Comparing these two meant that mtus between 1500 and
> 1518 did not trigger enabling jumbo frames.
>
> So instead compare the set mtu ETH_DATA_LEN, which is equal to
> JMS_MIN_SIZE - ETH_HLEN - ETH_FCS_LEN;
>
> Also do a check that the requested mtu is actually greater than the
> minimum length, else we do not need to enable jumbo frames.
>
> In practice this only introduced a very small range of mtus that did not
> work properly. Newer chips allow 2000 byte large frames by default, and
> older chips allow 1536 bytes long, which is equivalent to an mtu of
> 1514. So effectivly only mtus of 1515~1517 were broken.
>
> Fixes: 6ae5834b983a ("net: dsa: b53: add MTU configuration support")
> Signed-off-by: Jonas Gorski <jonas.gorski@xxxxxxxxx>

Reviewed-by: Florian Fainelli <florian.fainelli@xxxxxxxxxxxx>
--
Florian