netdev - Re: [PATCH] net: bcmgenet: Fix FCS generation for fragmented skbuffs

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Date: Wed, 27 Dec 2023 10:30:48 +0100
From: Florian Fainelli <florian.fainelli@...adcom.com>
To: Adrian Cinal <adriancinal1@...il.com>, netdev@...r.kernel.org
Cc: opendmb@...il.com, bcm-kernel-feedback-list@...adcom.com
Subject: Re: [PATCH] net: bcmgenet: Fix FCS generation for fragmented skbuffs

Hello,

On 12/26/2023 6:19 PM, Adrian Cinal wrote:
> The flag DMA_TX_APPEND_CRC was written to the first (instead of the last)
> DMA descriptor in the TX path, with each descriptor corresponding to a
> single skbuff fragment (or the skbuff head). This lead to packets with no
> FCS appearing on the wire if the kernel allocated the packet in fragments,
> which would always happen when using PACKET_MMAP/TPACKET
> (cf. tpacket_fill_skb() in af_packet.c).

s/lead/leads/

> 
> Signed-off-by: Adrian Cinal <adriancinal1@...il.com>

This looks like we could have a Fixes: tag for this change because it 
does fix an actual bug:

Fixes: 1c1008c793fa ("net: bcmgenet: add main driver file")

thanks Adrian!

> ---
>   drivers/net/ethernet/broadcom/genet/bcmgenet.c | 10 +++++-----
>   1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/net/ethernet/broadcom/genet/bcmgenet.c b/drivers/net/ethernet/broadcom/genet/bcmgenet.c
> index 1174684a7f23..df4b0e557c76 100644
> --- a/drivers/net/ethernet/broadcom/genet/bcmgenet.c
> +++ b/drivers/net/ethernet/broadcom/genet/bcmgenet.c
> @@ -2137,16 +2137,16 @@ static netdev_tx_t bcmgenet_xmit(struct sk_buff *skb, struct net_device *dev)
>   		len_stat = (size << DMA_BUFLENGTH_SHIFT) |
>   			   (priv->hw_params->qtag_mask << DMA_TX_QTAG_SHIFT);
>   
> -		/* Note: if we ever change from DMA_TX_APPEND_CRC below we
> -		 * will need to restore software padding of "runt" packets
> -		 */
>   		if (!i) {
> -			len_stat |= DMA_TX_APPEND_CRC | DMA_SOP;
> +			len_stat |= DMA_SOP;
>   			if (skb->ip_summed == CHECKSUM_PARTIAL)
>   				len_stat |= DMA_TX_DO_CSUM;
>   		}
> +		/* Note: if we ever change from DMA_TX_APPEND_CRC below we
> +		 * will need to restore software padding of "runt" packets
> +		 */
>   		if (i == nr_frags)
> -			len_stat |= DMA_EOP;
> +			len_stat |= DMA_TX_APPEND_CRC | DMA_EOP;
>   
>   		dmadesc_set(priv, tx_cb_ptr->bd_addr, mapping, len_stat);
>   	}

-- 
Florian

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