[PATCH] net/nfp: fix the Tx descriptor free logic of nfd3

[Ferruh Yigit]

On 5/12/2023 3:07 AM, Chaoyong He wrote:
> In the tx descriptor free logic of nfd3, the former logic might force
> cast a negative number into a very big unsigned number, and which will
> cause potential problem in the xmit loop.
> 
> The xmit loop will continue in the place where it should break, and will
> overwrite the Tx descriptor which is not free to use by the PMD.
> 
> Fixes: 74a640dac864 ("net/nfp: avoid modulo operations for handling ring wrapping")
> Cc: stable at dpdk.org
> 
> Signed-off-by: Chaoyong He <chaoyong.he at corigine.com>
> Reviewed-by: Niklas Söderlund <niklas.soderlund at corigine.com>
> ---
>  drivers/net/nfp/nfp_rxtx.h | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/nfp/nfp_rxtx.h b/drivers/net/nfp/nfp_rxtx.h
> index 5e651518ed..e642bc970a 100644
> --- a/drivers/net/nfp/nfp_rxtx.h
> +++ b/drivers/net/nfp/nfp_rxtx.h
> @@ -401,10 +401,14 @@ nfp_net_mbuf_alloc_failed(struct nfp_net_rxq *rxq)
>  static inline uint32_t
>  nfp_net_nfd3_free_tx_desc(struct nfp_net_txq *txq)
>  {
> +	uint32_t free_desc;
> +
>  	if (txq->wr_p >= txq->rd_p)
> -		return txq->tx_count - (txq->wr_p - txq->rd_p) - 8;
> +		free_desc = txq->tx_count - (txq->wr_p - txq->rd_p);
>  	else
> -		return txq->rd_p - txq->wr_p - 8;
> +		free_desc = txq->rd_p - txq->wr_p;
> +
> +	return (free_desc > 8) ? (free_desc - 8) : 0;
>  }
>  
>  /*


Can you please rebase this patch on top of latest next-net?

'nfp_net_nfd3_free_tx_desc()' moved to 'drivers/net/nfp/nfd3/nfp_nfd3.h'
in commit '2344d6272fe9 ("net/nfp: move NFD3 logic to own source file")'