Re: [PATCH] net: mvneta: fix handling of the Tx descriptor counter

[Simon Guinot <simon.guinot@sequanux.org>]

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Hi Sven and Andreas,

Please, can you try with this patch ?

Thanks.

Simon

On Wed, Nov 08, 2017 at 05:58:35PM +0100, Simon Guinot wrote:
> The mvneta controller provides a 8-bit register to update the pending
> Tx descriptor counter. Then, a maximum of 255 Tx descriptors can be
> added at once. In the current code the mvneta_txq_pend_desc_add function
> assumes the caller takes care of this limit. But it is not the case. In
> some situations (xmit_more flag), more than 255 descriptors are added.
> When this happens, the Tx descriptor counter register is updated with a
> wrong value, which breaks the whole Tx queue management.
> 
> This patch fixes the issue by allowing the mvneta_txq_pend_desc_add
> function to process more than 255 Tx descriptors.
> 
> Fixes: 2a90f7e1d5d0 ("net: mvneta: add xmit_more support")
> Cc: stable@vger.kernel.org # 4.11+
> Signed-off-by: Simon Guinot <simon.guinot@sequanux.org>
> ---
>  drivers/net/ethernet/marvell/mvneta.c | 16 +++++++++-------
>  1 file changed, 9 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/net/ethernet/marvell/mvneta.c b/drivers/net/ethernet/marvell/mvneta.c
> index 64a04975bcf8..027c08ce4e5d 100644
> --- a/drivers/net/ethernet/marvell/mvneta.c
> +++ b/drivers/net/ethernet/marvell/mvneta.c
> @@ -816,11 +816,14 @@ static void mvneta_txq_pend_desc_add(struct mvneta_port *pp,
>  {
>  	u32 val;
>  
> -	/* Only 255 descriptors can be added at once ; Assume caller
> -	 * process TX desriptors in quanta less than 256
> -	 */
> -	val = pend_desc + txq->pending;
> -	mvreg_write(pp, MVNETA_TXQ_UPDATE_REG(txq->id), val);
> +	pend_desc += txq->pending;
> +
> +	/* Only 255 Tx descriptors can be added at once */
> +	while (pend_desc > 0) {
> +		val = min(pend_desc, 255);
> +		mvreg_write(pp, MVNETA_TXQ_UPDATE_REG(txq->id), val);
> +		pend_desc -= val;
> +	}
>  	txq->pending = 0;
>  }
>  
> @@ -2413,8 +2416,7 @@ static int mvneta_tx(struct sk_buff *skb, struct net_device *dev)
>  		if (txq->count >= txq->tx_stop_threshold)
>  			netif_tx_stop_queue(nq);
>  
> -		if (!skb->xmit_more || netif_xmit_stopped(nq) ||
> -		    txq->pending + frags > MVNETA_TXQ_DEC_SENT_MASK)
> +		if (!skb->xmit_more || netif_xmit_stopped(nq))
>  			mvneta_txq_pend_desc_add(pp, txq, frags);
>  		else
>  			txq->pending += frags;
> -- 
> 2.9.3

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