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

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Message-ID: <aedc55c4-9a76-480e-afc0-105991aac04a@genexis.eu>
Date: Fri, 16 Jan 2026 16:05:41 +0100
From: Benjamin Larsson <benjamin.larsson@...exis.eu>
To: Andrew Lunn <andrew@...n.ch>, sayantan nandy <sayantann11@...il.com>
Cc: lorenzo@...nel.org, 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, rajeev.kumar@...oha.com
Subject: Re: [PATCH] net: airoha_eth: increase max mtu to 9220 for DSA jumbo
 frames

On 16/01/2026 15:56, Andrew Lunn wrote:
> On Fri, Jan 16, 2026 at 08:09:51PM +0530, sayantan nandy wrote:
>> Hi all,
>>
>> Thanks for the review and comments.
>>
>> I checked the AN7581 HW and it does support MTU sizes up to 16K. However, as
>> mentioned by Benjamin, larger packets consume more DMA descriptors, and while
>> no extra buffers are allocated, this can put pressure on the descriptor rings.
> Does the hardware consume DMA descriptors for the full 16K, not just
> the number of descriptors needed for the actual received packet size?
> That seems like a bad design.
>
>        Andrew

The descriptor buffer size is configurable. The amount of used 
descriptors will be the received packet size % descriptor buffer size + 1.

MvH

Benjamin Larsson