netdev - Re: [PATCH net] net: xilinx: axienet: Fix Tx skb circular buffer occupancy check in dmaengine xmit

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Message-ID: <57443336-2098-42c9-be6d-468cdbd9b312@linux.dev>
Date: Fri, 23 May 2025 12:20:26 -0400
From: Sean Anderson <sean.anderson@...ux.dev>
To: Suraj Gupta <suraj.gupta2@....com>, andrew+netdev@...n.ch,
 davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
 pabeni@...hat.com, michal.simek@....com, radhey.shyam.pandey@....com,
 horms@...nel.org
Cc: netdev@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 linux-kernel@...r.kernel.org, git@....com, harini.katakam@....com
Subject: Re: [PATCH net] net: xilinx: axienet: Fix Tx skb circular buffer
 occupancy check in dmaengine xmit

On 5/21/25 14:16, Suraj Gupta wrote:
> In Dmaengine flow, driver maintains struct skbuf_dma_descriptor rings each
> element of which corresponds to a skb. In Tx datapath, compare available
> space in skb ring with number of skbs instead of skb fragments.
> Replace x * (MAX_SKB_FRAGS) in netif_txq_completed_wake() and
> netif_txq_maybe_stop() with x * (1 skb) to fix the comparison.
> 
> Fixes: 6a91b846af85 ("net: axienet: Introduce dmaengine support")
> Signed-off-by: Suraj Gupta <suraj.gupta2@....com>
> ---
>  drivers/net/ethernet/xilinx/xilinx_axienet_main.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/net/ethernet/xilinx/xilinx_axienet_main.c b/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
> index 1b7a653c1f4e..6011d7eae0c7 100644
> --- a/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
> +++ b/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
> @@ -880,7 +880,7 @@ static void axienet_dma_tx_cb(void *data, const struct dmaengine_result *result)
>  	dev_consume_skb_any(skbuf_dma->skb);
>  	netif_txq_completed_wake(txq, 1, len,
>  				 CIRC_SPACE(lp->tx_ring_head, lp->tx_ring_tail, TX_BD_NUM_MAX),
> -				 2 * MAX_SKB_FRAGS);
> +				 2);
>  }
>  
>  /**
> @@ -914,7 +914,7 @@ axienet_start_xmit_dmaengine(struct sk_buff *skb, struct net_device *ndev)
>  
>  	dma_dev = lp->tx_chan->device;
>  	sg_len = skb_shinfo(skb)->nr_frags + 1;
> -	if (CIRC_SPACE(lp->tx_ring_head, lp->tx_ring_tail, TX_BD_NUM_MAX) <= sg_len) {
> +	if (CIRC_SPACE(lp->tx_ring_head, lp->tx_ring_tail, TX_BD_NUM_MAX) <= 1) {
>  		netif_stop_queue(ndev);
>  		if (net_ratelimit())
>  			netdev_warn(ndev, "TX ring unexpectedly full\n");
> @@ -964,7 +964,7 @@ axienet_start_xmit_dmaengine(struct sk_buff *skb, struct net_device *ndev)
>  	txq = skb_get_tx_queue(lp->ndev, skb);
>  	netdev_tx_sent_queue(txq, skb->len);
>  	netif_txq_maybe_stop(txq, CIRC_SPACE(lp->tx_ring_head, lp->tx_ring_tail, TX_BD_NUM_MAX),
> -			     MAX_SKB_FRAGS + 1, 2 * MAX_SKB_FRAGS);
> +			     1, 2);
>  
>  	dmaengine_submit(dma_tx_desc);
>  	dma_async_issue_pending(lp->tx_chan);

Reviwed-by: Sean Anderson <sean.anderson@...ux.dev>