Re: [PATCH net v3] net: wwan: qcom_bam_dmux: account network packets

[Dmitry Sinyavin <sinyavin@gmail.com>]

The delayed Sashiko review of v2 identified a valid teardown race that 
also affects v3. I will address it in v4.

pw-bot: changes-requested

02.09.2026 14:45, Dmitry Sinyavin wrote:
> The BAM-DMUX data path does not update the network device packet and byte
> counters. As a result, userspace sees zero traffic even while packets are
> being transferred.
> 
> Use the standard per-CPU software statistics helpers. Account transmitted
> packets after their DMA completion and received packets after removing the
> BAM-DMUX header and padding.
> 
> Fixes: 21a0ffd9b38c ("net: wwan: Add Qualcomm BAM-DMUX WWAN network driver")
> Signed-off-by: Dmitry Sinyavin <sinyavin@gmail.com>
> Reviewed-by: Loic Poulain <loic.poulain@oss.qualcomm.com>
> ---
> v3:
> - Count packets discarded by the transmit error path.
> 
> v2:
> - Read the TX payload length after unmapping the DMA buffer and combine the
>    network-device checks.
> 
> v2: https://lore.kernel.org/netdev/20260831181006.1382372-1-sinyavin@gmail.com/
> v1: https://lore.kernel.org/netdev/20260830085400.2542956-1-sinyavin@gmail.com/
> 
> Build-tested for ARM with Clang and W=1 using allmodconfig and allyesconfig.
> Hardware-tested on an MDM9607-based device: three 32-byte ICMP probes completed
> without loss, and the RX and TX counters each advanced by three packets and
> 180 bytes.
> 
>   drivers/net/wwan/qcom_bam_dmux.c | 8 ++++++++
>   1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/net/wwan/qcom_bam_dmux.c b/drivers/net/wwan/qcom_bam_dmux.c
> index cc6ace8d6437..ef3356200b3e 100644
> --- a/drivers/net/wwan/qcom_bam_dmux.c
> +++ b/drivers/net/wwan/qcom_bam_dmux.c
> @@ -177,8 +177,12 @@ static void bam_dmux_tx_callback(void *data)
>   {
>   	struct bam_dmux_skb_dma *skb_dma = data;
>   	struct sk_buff *skb = skb_dma->skb;
> +	struct net_device *netdev = skb->dev;
>   
>   	bam_dmux_tx_done(skb_dma);
> +	if (netdev)
> +		dev_sw_netstats_tx_add(netdev, 1,
> +				       ((struct bam_dmux_hdr *)skb->data)->len);
>   	dev_consume_skb_any(skb);
>   }
>   
> @@ -368,6 +372,7 @@ static netdev_tx_t bam_dmux_netdev_start_xmit(struct sk_buff *skb,
>   
>   drop:
>   	bam_dmux_tx_done(skb_dma);
> +	dev_core_stats_tx_dropped_inc(netdev);
>   	dev_kfree_skb_any(skb);
>   	return NETDEV_TX_OK;
>   }
> @@ -402,6 +407,7 @@ static const struct net_device_ops bam_dmux_ops = {
>   	.ndo_open	= bam_dmux_netdev_open,
>   	.ndo_stop	= bam_dmux_netdev_stop,
>   	.ndo_start_xmit	= bam_dmux_netdev_start_xmit,
> +	.ndo_get_stats64	= dev_get_tstats64,
>   };
>   
>   static const struct device_type wwan_type = {
> @@ -421,6 +427,7 @@ static void bam_dmux_netdev_setup(struct net_device *dev)
>   	dev->needed_headroom = sizeof(struct bam_dmux_hdr);
>   	dev->needed_tailroom = sizeof(u32); /* word-aligned */
>   	dev->tx_queue_len = DEFAULT_TX_QUEUE_LEN;
> +	dev->pcpu_stat_type = NETDEV_PCPU_STAT_TSTATS;
>   
>   	/* This perm addr will be used as interface identifier by IPv6 */
>   	dev->addr_assign_type = NET_ADDR_RANDOM;
> @@ -533,6 +540,7 @@ static void bam_dmux_cmd_data(struct bam_dmux_skb_dma *skb_dma)
>   		break;
>   	}
>   
> +	dev_sw_netstats_rx_add(netdev, skb->len);
>   	netif_receive_skb(skb);
>   }
>   
> 
> base-commit: 2188569e7e1b0bc3f3b557dc97ab7a02befc11c8