linux-kernel - Re: [PATCH v3 net] net: enetc: do not transmit redirected XDP frames when the link is down

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Message-ID: <aTqkVJGREUi/fZ4J@test-OptiPlex-Tower-Plus-7010>
Date: Thu, 11 Dec 2025 16:30:36 +0530
From: Hariprasad Kelam <hkelam@...vell.com>
To: Wei Fang <wei.fang@....com>
CC: <claudiu.manoil@....com>, <vladimir.oltean@....com>,
        <xiaoning.wang@....com>, <andrew+netdev@...n.ch>,
        <davem@...emloft.net>, <edumazet@...gle.com>, <kuba@...nel.org>,
        <pabeni@...hat.com>, <ast@...nel.org>, <daniel@...earbox.net>,
        <hawk@...nel.org>, <john.fastabend@...il.com>, <sdf@...ichev.me>,
        <frank.li@....com>, <imx@...ts.linux.dev>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <bpf@...r.kernel.org>
Subject: Re: [PATCH v3 net] net: enetc: do not transmit redirected XDP frames
 when the link is down

On 2025-12-11 at 07:39:19, Wei Fang (wei.fang@....com) wrote:
> In the current implementation, the enetc_xdp_xmit() always transmits
> redirected XDP frames even if the link is down, but the frames cannot
> be transmitted from TX BD rings when the link is down, so the frames
> are still kept in the TX BD rings. If the XDP program is uninstalled,
> users will see the following warning logs.
> 
> fsl_enetc 0000:00:00.0 eno0: timeout for tx ring #6 clear
> 
> More worse, the TX BD ring cannot work properly anymore, because the
> HW PIR and CIR are not equal after the re-initialization of the TX
> BD ring. At this point, the BDs between CIR and PIR are invalid,
> which will cause a hardware malfunction.
> 
> Another reason is that there is internal context in the ring prefetch
> logic that will retain the state from the first incarnation of the ring
> and continue prefetching from the stale location when we re-initialize
> the ring. The internal context is only reset by an FLR. That is to say,
> for LS1028A ENETC, software cannot set the HW CIR and PIR when
> initializing the TX BD ring.
> 
> It does not make sense to transmit redirected XDP frames when the link is
> down. Add a link status check to prevent transmission in this condition.
> This fixes part of the issue, but more complex cases remain. For example,
> the TX BD ring may still contain unsent frames when the link goes down.
> Those situations require additional patches, which will build on this
> one.
> 
> Fixes: 9d2b68cc108d ("net: enetc: add support for XDP_REDIRECT")
> Signed-off-by: Wei Fang <wei.fang@....com>
> Reviewed-by: Frank Li <Frank.Li@....com>
> 
> ---
> v3 changes:
> 1. Improve the commit message
> 2. Collect Reviewed-by tag
> v2: https://lore.kernel.org/imx/20251209135445.3443732-1-wei.fang@nxp.com/
> v2 changes:
> Improve the commit message
> v1: https://lore.kernel.org/imx/20251205105307.2756994-1-wei.fang@nxp.com/
> ---
>  drivers/net/ethernet/freescale/enetc/enetc.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/freescale/enetc/enetc.c b/drivers/net/ethernet/freescale/enetc/enetc.c
> index 0535e92404e3..f410c245ea91 100644
> --- a/drivers/net/ethernet/freescale/enetc/enetc.c
> +++ b/drivers/net/ethernet/freescale/enetc/enetc.c
> @@ -1778,7 +1778,8 @@ int enetc_xdp_xmit(struct net_device *ndev, int num_frames,
>  	int xdp_tx_bd_cnt, i, k;
>  	int xdp_tx_frm_cnt = 0;
>  
> -	if (unlikely(test_bit(ENETC_TX_DOWN, &priv->flags)))
> +	if (unlikely(test_bit(ENETC_TX_DOWN, &priv->flags) ||
> +		     !netif_carrier_ok(ndev)))
>  		return -ENETDOWN;
>  
>  	enetc_lock_mdio();
> -- 
> 2.34.1
> 
Reviewed-by: Hariprasad Kelam <hkelam@...vell.com>