netdev - Re: [PATCH net-next v3] net: airoha_eth: increase max MTU to 9220 for DSA jumbo frames

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Message-ID: <aW5Yay8rDupPfB-H@lore-desk>
Date: Mon, 19 Jan 2026 17:14:35 +0100
From: Lorenzo Bianconi <lorenzo@...nel.org>
To: Sayantan Nandy <sayantann11@...il.com>
Cc: linux-arm-kernel@...ts.infradead.org,
	linux-mediatek@...ts.infradead.org, netdev@...r.kernel.org,
	sayantan.nandy@...oha.com, bread.hsu@...oha.com,
	kuldeep.malik@...oha.com, aniket.negi@...oha.com,
	brown.huang@...oha.com
Subject: Re: [PATCH net-next v3] net: airoha_eth: increase max MTU to 9220
 for DSA jumbo frames

> 
> The industry standard jumbo frame MTU is 9216 bytes. When using the DSA
> subsystem, a 4-byte tag is added to each Ethernet frame.
> 
> Increase AIROHA_MAX_MTU to 9220 bytes (9216 + 4) so that users can set a
> standard 9216-byte MTU on DSA ports.
> 
> The underlying hardware supports significantly larger frame sizes
> (approximately 16K). However, the maximum MTU is limited to 9220 bytes
> for now, as this is sufficient to support standard jumbo frames and does
> not incur additional memory allocation overhead.
> 
> 
> Signed-off-by: Sayantan Nandy <sayantann11@...il.com>

Acked-by: Lorenzo Bianconi <lorenzo@...nel.org>

> ---
> v3:
> - Document that hardware supports larger MTU (~16K), but limit to 9220 for now
> - Target net-next (netdev/main) as this is a feature enhancement
> - No functional changes
> 
> v2:
> - Clarified commit message regarding DSA tag overhead
> 
>  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
> 

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