linux-kernel - RE: [PATCH v2 net-next 3/5] et: fec: add rx_frame

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Message-ID:
 <PAXPR04MB918588241A96C60E7E7E4FE2893DA@PAXPR04MB9185.eurprd04.prod.outlook.com>
Date: Fri, 22 Aug 2025 13:33:09 +0000
From: Shenwei Wang <shenwei.wang@....com>
To: Wei Fang <wei.fang@....com>
CC: Clark Wang <xiaoning.wang@....com>, Stanislav Fomichev <sdf@...ichev.me>,
	"imx@...ts.linux.dev" <imx@...ts.linux.dev>, "netdev@...r.kernel.org"
	<netdev@...r.kernel.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, dl-linux-imx <linux-imx@....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>
Subject: RE: [PATCH v2 net-next 3/5] et: fec: add rx_frame_size to support
 configurable RX length



> -----Original Message-----
> From: Wei Fang <wei.fang@....com>
> Sent: Friday, August 22, 2025 5:10 AM
> To: Shenwei Wang <shenwei.wang@....com>
> Cc: Clark Wang <xiaoning.wang@....com>; Stanislav Fomichev
> <sdf@...ichev.me>; imx@...ts.linux.dev; netdev@...r.kernel.org; linux-
> kernel@...r.kernel.org; dl-linux-imx <linux-imx@....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>
> Subject: RE: [PATCH v2 net-next 3/5] et: fec: add rx_frame_size to support
> configurable RX length
> 
> > @@ -4563,6 +4563,7 @@ fec_probe(struct platform_device *pdev)
> >  	pinctrl_pm_select_sleep_state(&pdev->dev);
> >
> >  	fep->pagepool_order = 0;
> > +	fep->rx_frame_size = FEC_ENET_RX_FRSIZE;
> 
> According to the RM, to allow one maximum size frame per buffer,
> FEC_R_BUFF_SIZE must be set to FEC_R_CNTRL [MAX_FL] or larger.
> FEC_ENET_RX_FRSIZE is greater than PKT_MAXBUF_SIZE, I'm not sure whether it
> will cause some unknown issues.

MAX_FL defines the maximum allowable frame length, while TRUNC_FL specifies the threshold beyond 
which frames are truncated. Based on this logic, the documentation appears to be incorrect-TRUNC_FL 
should never exceed MAX_FL, as doing so would make the truncation mechanism ineffective. 

This has been confirmed through testing data.

Regards,
Shenwei

> 
> >  	fep->max_buf_size = PKT_MAXBUF_SIZE;
> >  	ndev->max_mtu = fep->max_buf_size - ETH_HLEN - ETH_FCS_LEN;