Re: [PATCH] net: airoha_eth: increase max mtu to 9220 for DSA jumbo frames

[Benjamin Larsson <benjamin.larsson@genexis.eu>]

On 1/15/26 09:48, Sayantan Nandy wrote:
> [You don't often get email from sayantann11@gmail.com. Learn why this is important at https://aka.ms/LearnAboutSenderIdentification ]
> 
> The Industry standard for jumbo frame MTU is 9216 bytes. When using DSA
> sub-system, an extra 4 byte tag is added to each frame. To allow users
> to set the standard 9216-byte MTU via ifconfig,increase AIROHA_MAX_MTU
> to 9220 bytes (9216+4).
> 
> Signed-off-by: Sayantan Nandy <sayantann11@gmail.com>
> ---
>   drivers/net/ethernet/airoha/airoha_eth.h | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/airoha/airoha_eth.h b/drivers/net/ethernet/airoha/airoha_eth.h
> index fbbc58133364..20e602d61e61 100644
> --- a/drivers/net/ethernet/airoha/airoha_eth.h
> +++ b/drivers/net/ethernet/airoha/airoha_eth.h
> @@ -21,7 +21,7 @@
>   #define AIROHA_MAX_NUM_IRQ_BANKS       4
>   #define AIROHA_MAX_DSA_PORTS           7
>   #define AIROHA_MAX_NUM_RSTS            3
> -#define AIROHA_MAX_MTU                 9216
> +#define AIROHA_MAX_MTU                 9220
>   #define AIROHA_MAX_PACKET_SIZE         2048
>   #define AIROHA_NUM_QOS_CHANNELS                4
>   #define AIROHA_NUM_QOS_QUEUES          8
> --
> 2.43.0


Hi, for reference the hardware datasheets lists support for jumbo frame 
sizes up to 16k.

In the Airoha case the MTK-DSA tag is transmitted out of band via the 
dma descriptor. I am not sure how this affects the frame size, it might 
be opaque in the actual hardware.

MvH
Benjamin Larsson