linux-kernel - [PATCH v2 net-next 4/5] net: fec: remove rx_align from fec_enet

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Message-Id: <20251117101921.1862427-5-wei.fang@nxp.com>
Date: Mon, 17 Nov 2025 18:19:20 +0800
From: Wei Fang <wei.fang@....com>
To: shenwei.wang@....com,
	xiaoning.wang@....com,
	andrew+netdev@...n.ch,
	davem@...emloft.net,
	edumazet@...gle.com,
	kuba@...nel.org,
	pabeni@...hat.com,
	eric@...int.com,
	Frank.Li@....com
Cc: imx@...ts.linux.dev,
	netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH v2 net-next 4/5] net: fec: remove rx_align from fec_enet_private

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
FEC_ENET_XDP_HEADROOM which is 256 bytes, so the RX buffer is always
64-byte aligned. Therefore, rx_align has no effect since that commit,
and we can safely remove it.

In addition, to prevent future modifications to FEC_ENET_XDP_HEADROOM,
a BUILD_BUG_ON() test has been added to the driver, which ensures that
FEC_ENET_XDP_HEADROOM provides the required alignment.

Signed-off-by: Wei Fang <wei.fang@....com>
---
 drivers/net/ethernet/freescale/fec.h      |  1 -
 drivers/net/ethernet/freescale/fec_main.c | 19 ++++++++++++++-----
 2 files changed, 14 insertions(+), 6 deletions(-)

diff --git a/drivers/net/ethernet/freescale/fec.h b/drivers/net/ethernet/freescale/fec.h
index c5bbc2c16a4f..a25dca9c7d71 100644
--- a/drivers/net/ethernet/freescale/fec.h
+++ b/drivers/net/ethernet/freescale/fec.h
@@ -660,7 +660,6 @@ struct fec_enet_private {
 	struct pm_qos_request pm_qos_req;
 
 	unsigned int tx_align;
-	unsigned int rx_align;
 
 	/* hw interrupt coalesce */
 	unsigned int rx_pkts_itr;
diff --git a/drivers/net/ethernet/freescale/fec_main.c b/drivers/net/ethernet/freescale/fec_main.c
index 1408e3e6650a..785bae8e1699 100644
--- a/drivers/net/ethernet/freescale/fec_main.c
+++ b/drivers/net/ethernet/freescale/fec_main.c
@@ -3435,6 +3435,19 @@ fec_enet_alloc_rxq_buffers(struct net_device *ndev, unsigned int queue)
 		return err;
 	}
 
+	/* Some platforms require the RX buffer must be 64 bytes alignment.
+	 * Some platforms require 16 bytes alignment. And some platforms
+	 * require 4 bytes alignment. But since the page pool have been
+	 * introduced into the driver, the address of RX buffer is always
+	 * the page address plus FEC_ENET_XDP_HEADROOM, and
+	 * FEC_ENET_XDP_HEADROOM is 256 bytes. Therefore, this address can
+	 * satisfy all platforms. To prevent future modifications to
+	 * FEC_ENET_XDP_HEADROOM from ignoring this hardware limitation, a
+	 * BUILD_BUG_ON() test has been added, which ensures that
+	 * FEC_ENET_XDP_HEADROOM provides the required alignment.
+	 */
+	BUILD_BUG_ON(FEC_ENET_XDP_HEADROOM & 0x3f);
+
 	for (i = 0; i < rxq->bd.ring_size; i++) {
 		page = page_pool_dev_alloc_pages(rxq->page_pool);
 		if (!page)
@@ -4069,10 +4082,8 @@ static int fec_enet_init(struct net_device *ndev)
 
 	WARN_ON(dsize != (1 << dsize_log2));
 #if defined(CONFIG_ARM) || defined(CONFIG_ARM64)
-	fep->rx_align = 0xf;
 	fep->tx_align = 0xf;
 #else
-	fep->rx_align = 0x3;
 	fep->tx_align = 0x3;
 #endif
 	fep->rx_pkts_itr = FEC_ITR_ICFT_DEFAULT;
@@ -4161,10 +4172,8 @@ static int fec_enet_init(struct net_device *ndev)
 		fep->csum_flags |= FLAG_RX_CSUM_ENABLED;
 	}
 
-	if (fep->quirks & FEC_QUIRK_HAS_MULTI_QUEUES) {
+	if (fep->quirks & FEC_QUIRK_HAS_MULTI_QUEUES)
 		fep->tx_align = 0;
-		fep->rx_align = 0x3f;
-	}
 
 	ndev->hw_features = ndev->features;
 
-- 
2.34.1