[PATCH net v4] net: wwan: qcom_bam_dmux: account network packets

[Dmitry Sinyavin <sinyavin@gmail.com>]

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 the driver has prepared and accepted them, before returning
NETDEV_TX_OK. The asynchronous DMA completion may run after the network
device has been unregistered. Account 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>
---
v4:
- Move TX accounting from the asynchronous DMA completion to the transmit
  path, avoiding access to statistics after netdev unregistration.

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.

v3: https://lore.kernel.org/netdev/20260902124506.363174-1-sinyavin@gmail.com/
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.

Tested on a ZTE MF283V with an MDM9607. The modem registered on LTE and
three 32-byte ICMP echo requests increased both wwan0 RX and TX counters by
three packets and 180 bytes. Bringing the interface down afterwards produced
no DMA, BAM-DMUX, or kernel fault messages.

 drivers/net/wwan/qcom_bam_dmux.c | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/drivers/net/wwan/qcom_bam_dmux.c b/drivers/net/wwan/qcom_bam_dmux.c
index cc6ace8d6437..03360301c8ee 100644
--- a/drivers/net/wwan/qcom_bam_dmux.c
+++ b/drivers/net/wwan/qcom_bam_dmux.c
@@ -335,6 +335,7 @@ static netdev_tx_t bam_dmux_netdev_start_xmit(struct sk_buff *skb,
 	struct bam_dmux_netdev *bndev = netdev_priv(netdev);
 	struct bam_dmux *dmux = bndev->dmux;
 	struct bam_dmux_skb_dma *skb_dma;
+	unsigned int len = skb->len;
 	int active, ret;
 
 	skb_dma = bam_dmux_tx_queue(dmux, skb);
@@ -357,17 +358,19 @@ static netdev_tx_t bam_dmux_netdev_start_xmit(struct sk_buff *skb,
 		if (!atomic_long_fetch_or(BIT(skb_dma - dmux->tx_skbs),
 					  &dmux->tx_deferred_skb))
 			queue_pm_work(&dmux->tx_wakeup_work);
-		return NETDEV_TX_OK;
-	}
+	} else {
+		if (!bam_dmux_skb_dma_submit_tx(skb_dma))
+			goto drop;
 
-	if (!bam_dmux_skb_dma_submit_tx(skb_dma))
-		goto drop;
+		dma_async_issue_pending(dmux->tx);
+	}
 
-	dma_async_issue_pending(dmux->tx);
+	dev_sw_netstats_tx_add(netdev, 1, len);
 	return NETDEV_TX_OK;
 
 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 +405,7 @@ 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 +425,7 @@ 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 +538,7 @@ 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
-- 
2.53.0