netdev - Re: [PATCH v3 net-next 3/5] net: fec: add rx_frame

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Message-ID: <0abb2c91-3786-4926-b0e3-30b9e222424d@lunn.ch>
Date: Sat, 23 Aug 2025 21:11:24 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Shenwei Wang <shenwei.wang@....com>
Cc: Wei Fang <wei.fang@....com>, 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>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Jesper Dangaard Brouer <hawk@...nel.org>,
	John Fastabend <john.fastabend@...il.com>,
	Clark Wang <xiaoning.wang@....com>,
	Stanislav Fomichev <sdf@...ichev.me>, imx@...ts.linux.dev,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-imx@....com
Subject: Re: [PATCH v3 net-next 3/5] net: fec: add rx_frame_size to support
 configurable RX length

On Sat, Aug 23, 2025 at 02:01:08PM -0500, Shenwei Wang wrote:
> Add a new rx_frame_size member in the fec_enet_private structure to
> decouple frame size configuration from max_buf_size. This allows more
> precise control over RX frame length settings. It is particularly useful
> for Jumbo frame support because the RX frame size may possible larger than
> the allocated RX buffer.

Please could you extend that a little. What happens if the received
frame is bigger than the buffer? Does the hardware fragment it over
two buffers?

> 
> Configure TRUNC_FL (Frame Truncation Length) based on the RX buffer size.
> Frames exceeding this limit will be treated as error packets and dropped.

This bit confuses me. You want to allow rx_frame_size to be bigger
than the buffer size, but you also want to discard frames bigger than
the buffer size?

    Andrew

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