netdev - RE: [PATCH v2 net-next 4/5] net: fec: add change_mtu to support dynamic buffer allocation

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Message-ID:
 <PAXPR04MB91850A2E4ED6ED29D45BF27C893CA@PAXPR04MB9185.eurprd04.prod.outlook.com>
Date: Sat, 23 Aug 2025 18:38:39 +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 4/5] net: fec: add change_mtu to support
 dynamic buffer allocation



> -----Original Message-----
> From: Wei Fang <wei.fang@....com>
> Sent: Friday, August 22, 2025 4:49 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 4/5] net: fec: add change_mtu to support
> dynamic buffer allocation
> 
> > +static int fec_change_mtu(struct net_device *ndev, int new_mtu) {
> > +	struct fec_enet_private *fep = netdev_priv(ndev);
> > +	int order, done;
> > +	bool running;
> > +
> > +	order = get_order(new_mtu + ETH_HLEN + ETH_FCS_LEN);
> > +	if (fep->pagepool_order == order) {
> > +		WRITE_ONCE(ndev->mtu, new_mtu);
> > +		return 0;
> > +	}
> > +
> > +	fep->pagepool_order = order;
> > +	fep->rx_frame_size = (PAGE_SIZE << order) -
> FEC_ENET_XDP_HEADROOM
> > +			     - SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
> > +
> 
> I think we need to add a check for rx_frame_size, as FEC_R_CNTRL[MAX_FL] and
> FEC_FTRL[TRUNC_FL] only have 14 bits.

That would be redundant, since rx_frame_size cannot exceed max_buf_size which value
would either be PKT_MAXBUF_SIZE or MAX_JUMBO_BUF_SIZE.

Regards,
Shenwei