Commit ca1bb3fe authored by Clemens Gruber's avatar Clemens Gruber Committed by Paolo Abeni
Browse files

net: fec: account for VLAN header in frame length calculations 



The MAX_FL (maximum frame length) and related calculations used ETH_HLEN,
which does not account for the 4-byte VLAN tag in tagged frames. This
caused the hardware to reject valid VLAN frames as oversized, resulting
in RX errors and dropped packets.

Use VLAN_ETH_HLEN instead of ETH_HLEN in the MAX_FL register setup,
cut-through mode threshold, buffer allocation, and max_mtu calculation.

Cc: stable@kernel.org # v6.18+
Fixes: 62b5bb7b ("net: fec: update MAX_FL based on the current MTU")
Fixes: d466c160 ("net: fec: enable the Jumbo frame support for i.MX8QM")
Fixes: 59e9bf03 ("net: fec: add change_mtu to support dynamic buffer allocation")
Fixes: ec2a1681 ("net: fec: use a member variable for maximum buffer size")
Signed-off-by: default avatarClemens Gruber <mail@clemensgruber.at>
Reviewed-by: default avatarWei Fang <wei.fang@nxp.com>
Link: https://patch.msgid.link/20260121083751.66997-1-mail@clemensgruber.at


Signed-off-by: default avatarPaolo Abeni <pabeni@redhat.com>
parent cc4816bd

drivers/net/ethernet/freescale/fec_main.c

+7 −6
Original line number Diff line number Diff line
@@ -1150,7 +1150,7 @@ fec_restart(struct net_device *ndev) 
	u32 rcntl = FEC_RCR_MII;



	if (OPT_ARCH_HAS_MAX_FL)

		rcntl |= (fep->netdev->mtu + ETH_HLEN + ETH_FCS_LEN) << 16;

		rcntl |= (fep->netdev->mtu + VLAN_ETH_HLEN + ETH_FCS_LEN) << 16;



	if (fep->bufdesc_ex)

		fec_ptp_save_state(fep);
@@ -1285,12 +1285,13 @@ fec_restart(struct net_device *ndev) 


		/* When Jumbo Frame is enabled, the FIFO may not be large enough

		 * to hold an entire frame. In such cases, if the MTU exceeds

		 * (PKT_MAXBUF_SIZE - ETH_HLEN - ETH_FCS_LEN), configure the interface

		 * to operate in cut-through mode, triggered by the FIFO threshold.

		 * (PKT_MAXBUF_SIZE - VLAN_ETH_HLEN - ETH_FCS_LEN), configure

		 * the interface to operate in cut-through mode, triggered by

		 * the FIFO threshold.

		 * Otherwise, enable the ENET store-and-forward mode.

		 */

		if ((fep->quirks & FEC_QUIRK_JUMBO_FRAME) &&

		    (ndev->mtu > (PKT_MAXBUF_SIZE - ETH_HLEN - ETH_FCS_LEN)))

		    (ndev->mtu > (PKT_MAXBUF_SIZE - VLAN_ETH_HLEN - ETH_FCS_LEN)))

			writel(0xF, fep->hwp + FEC_X_WMRK);

		else

			writel(FEC_TXWMRK_STRFWD, fep->hwp + FEC_X_WMRK);
@@ -4037,7 +4038,7 @@ static int fec_change_mtu(struct net_device *ndev, int new_mtu) 
	if (netif_running(ndev))

		return -EBUSY;



	order = get_order(new_mtu + ETH_HLEN + ETH_FCS_LEN

	order = get_order(new_mtu + VLAN_ETH_HLEN + ETH_FCS_LEN

			  + FEC_DRV_RESERVE_SPACE);

	fep->rx_frame_size = (PAGE_SIZE << order) - FEC_DRV_RESERVE_SPACE;

	fep->pagepool_order = order;
@@ -4588,7 +4589,7 @@ fec_probe(struct platform_device *pdev) 
	else

		fep->max_buf_size = PKT_MAXBUF_SIZE;



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

	ndev->max_mtu = fep->max_buf_size - VLAN_ETH_HLEN - ETH_FCS_LEN;



	ret = register_netdev(ndev);

	if (ret)