[PATCH net-next v7 2/3] net: airoha: fix ETS QoS stats counter underflow and cross-channel corruption

[Lorenzo Bianconi <lorenzo@kernel.org>]

airoha_qdma_get_tx_ets_stats() has two bugs:
- The hardware counters read via airoha_qdma_rr() are 32-bit values
  but are stored in u64 locals and subtracted from u64 baselines. When
  a 32-bit hardware counter wraps around, the subtraction produces a
  large underflow value passed to _bstats_update().
- The baseline counters (cpu_tx_packets, fwd_tx_packets) are stored as
  single per-device fields, but airoha_qdma_get_tx_ets_stats() is
  called with different channel values (0-3). Each call reads a
  different channel's hardware counter but overwrites the same
  baseline, corrupting the delta computation for other channels.

Fix both by:
- Narrowing the counter locals and baselines to u32 so that 32-bit
  unsigned subtraction handles wrap-around naturally.
- Grouping the baselines into a per-channel qos_stats array so each
  channel tracks its own previous counter value independently.

Fixes: 20bf7d07c956 ("net: airoha: Add sched ETS offload support")
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
---
 drivers/net/ethernet/airoha/airoha_eth.c | 18 +++++++++++-------
 drivers/net/ethernet/airoha/airoha_eth.h |  7 ++++---
 2 files changed, 15 insertions(+), 10 deletions(-)

diff --git a/drivers/net/ethernet/airoha/airoha_eth.c b/drivers/net/ethernet/airoha/airoha_eth.c
index 8bba54ebcf07..2c9ceb9f16f8 100644
--- a/drivers/net/ethernet/airoha/airoha_eth.c
+++ b/drivers/net/ethernet/airoha/airoha_eth.c
@@ -2491,16 +2491,20 @@ static int airoha_qdma_get_tx_ets_stats(struct net_device *netdev, int channel,
 {
 	struct airoha_gdm_dev *dev = netdev_priv(netdev);
 	struct airoha_qdma *qdma = dev->qdma;
+	u32 cpu_tx_packets, fwd_tx_packets;
+	u64 tx_packets;
 
-	u64 cpu_tx_packets = airoha_qdma_rr(qdma, REG_CNTR_VAL(channel << 1));
-	u64 fwd_tx_packets = airoha_qdma_rr(qdma,
-					    REG_CNTR_VAL((channel << 1) + 1));
-	u64 tx_packets = (cpu_tx_packets - dev->cpu_tx_packets) +
-			 (fwd_tx_packets - dev->fwd_tx_packets);
+	cpu_tx_packets = airoha_qdma_rr(qdma, REG_CNTR_VAL(channel << 1));
+	fwd_tx_packets = airoha_qdma_rr(qdma,
+					REG_CNTR_VAL((channel << 1) + 1));
+	tx_packets = (u32)(cpu_tx_packets -
+			   dev->qos_stats[channel].cpu_tx_packets) +
+		     (u32)(fwd_tx_packets -
+			   dev->qos_stats[channel].fwd_tx_packets);
 
 	_bstats_update(opt->stats.bstats, 0, tx_packets);
-	dev->cpu_tx_packets = cpu_tx_packets;
-	dev->fwd_tx_packets = fwd_tx_packets;
+	dev->qos_stats[channel].cpu_tx_packets = cpu_tx_packets;
+	dev->qos_stats[channel].fwd_tx_packets = fwd_tx_packets;
 
 	return 0;
 }
diff --git a/drivers/net/ethernet/airoha/airoha_eth.h b/drivers/net/ethernet/airoha/airoha_eth.h
index 87ab3ea10664..ac5f571f3e53 100644
--- a/drivers/net/ethernet/airoha/airoha_eth.h
+++ b/drivers/net/ethernet/airoha/airoha_eth.h
@@ -545,9 +545,10 @@ struct airoha_gdm_dev {
 	struct airoha_eth *eth;
 
 	DECLARE_BITMAP(qos_sq_bmap, AIROHA_NUM_QOS_CHANNELS);
-	/* qos stats counters */
-	u64 cpu_tx_packets;
-	u64 fwd_tx_packets;
+	struct {
+		u32 cpu_tx_packets;
+		u32 fwd_tx_packets;
+	} qos_stats[AIROHA_NUM_QOS_CHANNELS];
 
 	u32 flags;
 	int nbq;

-- 
2.54.0