linux-kernel - Re: [PATCH net] net: fec: ERR007885 Workaround for XDP TX path

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Message-ID: <cfc92b7c-b376-4de0-83a7-f7080c6f24d9@redhat.com>
Date: Thu, 4 Dec 2025 09:53:55 +0100
From: Paolo Abeni <pabeni@...hat.com>
To: Wei Fang <wei.fang@....com>, shenwei.wang@....com, xiaoning.wang@....com,
 andrew+netdev@...n.ch, davem@...emloft.net, edumazet@...gle.com,
 kuba@...nel.org
Cc: imx@...ts.linux.dev, netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] net: fec: ERR007885 Workaround for XDP TX path

On 11/28/25 3:59 AM, Wei Fang wrote:
> The ERR007885 will lead to a TDAR race condition for mutliQ when the
> driver sets TDAR and the UDMA clears TDAR simultaneously or in a small
> window (2-4 cycles). And it will cause the udma_tx and udma_tx_arbiter
> state machines to hang. Therefore, the commit 53bb20d1faba ("net: fec:
> add variable reg_desc_active to speed things up") and the commit
> a179aad12bad ("net: fec: ERR007885 Workaround for conventional TX") have
> added the workaround to fix the potential issue for the conventional TX
> path. Similarly, the XDP TX path should also have the potential hang
> issue, so add the workaround for XDP TX path.
> 
> Fixes: 6d6b39f180b8 ("net: fec: add initial XDP support")
> Signed-off-by: Wei Fang <wei.fang@....com>
> ---
>  drivers/net/ethernet/freescale/fec_main.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/freescale/fec_main.c b/drivers/net/ethernet/freescale/fec_main.c
> index 3222359ac15b..e2b75d1970ae 100644
> --- a/drivers/net/ethernet/freescale/fec_main.c
> +++ b/drivers/net/ethernet/freescale/fec_main.c
> @@ -3948,7 +3948,12 @@ static int fec_enet_txq_xmit_frame(struct fec_enet_private *fep,
>  	txq->bd.cur = bdp;
>  
>  	/* Trigger transmission start */
> -	writel(0, txq->bd.reg_desc_active);
> +	if (!(fep->quirks & FEC_QUIRK_ERR007885) ||
> +	    !readl(txq->bd.reg_desc_active) ||
> +	    !readl(txq->bd.reg_desc_active) ||
> +	    !readl(txq->bd.reg_desc_active) ||
> +	    !readl(txq->bd.reg_desc_active))
> +		writel(0, txq->bd.reg_desc_active);
>  
>  	return 0;
>  }

LGTM!

Side note for a net-next follow-up: please consider moving this logic in
a reusable helper, since you already have a few potentials call sites.

/P