linux-kernel - RE: [PATCH net-next 4/5] net: fec: remove rx_align from fec_enet

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Message-ID:
 <PAXPR04MB85109979C5B15727F510F87188CDA@PAXPR04MB8510.eurprd04.prod.outlook.com>
Date: Thu, 13 Nov 2025 01:40:15 +0000
From: Wei Fang <wei.fang@....com>
To: Andrew Lunn <andrew@...n.ch>
CC: Shenwei Wang <shenwei.wang@....com>, Clark Wang <xiaoning.wang@....com>,
	"andrew+netdev@...n.ch" <andrew+netdev@...n.ch>, "davem@...emloft.net"
	<davem@...emloft.net>, "edumazet@...gle.com" <edumazet@...gle.com>,
	"kuba@...nel.org" <kuba@...nel.org>, "pabeni@...hat.com" <pabeni@...hat.com>,
	"eric@...int.com" <eric@...int.com>, "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>
Subject: RE: [PATCH net-next 4/5] net: fec: remove rx_align from
 fec_enet_private

> On Tue, Nov 11, 2025 at 06:00:56PM +0800, Wei Fang wrote:
> > The rx_align was introduced by the commit 41ef84ce4c72 ("net: fec:
> > change FEC alignment according to i.mx6 sx requirement"). Because the
> > i.MX6 SX requires RX buffer must be 64 bytes alignment.
> >
> > Since the commit 95698ff6177b ("net: fec: using page pool to manage RX
> > buffers"), the address of the RX buffer is always the page address
> > plus
> > 128 bytes, so RX buffer is always 64-byte aligned.
> 
> It is not obvious to me where this 128 bytes is added.
> 

Sorry, I misremembered the value of XDP_PACKET_HEADROOM. it should
be 256 bytes.

See fec_enet_alloc_rxq_buffers():

phys_addr = page_pool_get_dma_addr(page) + FEC_ENET_XDP_HEADROOM;
bdp->cbd_bufaddr = cpu_to_fec32(phys_addr);

I will correct it in v2, thanks