[PATCH net-next 1/3] net: bcmgenet: collapse TX priority queues to a single queue

[Nicolai Buchwitz]

The strict-priority TX queues can starve under multi-queue load and
trip NETDEV_WATCHDOG. Justin's earlier series [1] worked around the
symptom but kept the design.

The multi-queue design was originally used for STB use cases that are
no longer needed, as confirmed by Justin. v1 hw_params already
exercises a single-queue path. Point v2-v4 at the same configuration:
ring 0 takes the full BD pool, every per-ring loop collapses to one
iteration, and netif_set_real_num_tx_queues drops to 1 via the
existing tx_queues + 1 arithmetic.

Tested on Raspberry Pi CM4 (BCM2711). The baseline kernel trips
NETDEV_WATCHDOG within seconds under iperf3 UDP saturation
(-u -b0 -P16 -t60). After the change the same test completes
without a watchdog, and a single-stream 60 s UDP run sustains
956 Mbit/s with 0/4952890 datagrams lost. Single-stream TCP
throughput is unchanged at 943 Mbit/s.

[1] https://lore.kernel.org/netdev/20260406175756.134567-1-justin.chen@xxxxxxxxxxxx/

Signed-off-by: Nicolai Buchwitz <nb@xxxxxxxxxxx>
---
 drivers/net/ethernet/broadcom/genet/bcmgenet.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/drivers/net/ethernet/broadcom/genet/bcmgenet.c b/drivers/net/ethernet/broadcom/genet/bcmgenet.c
index ca403581357d..c892734b4cd0 100644
--- a/drivers/net/ethernet/broadcom/genet/bcmgenet.c
+++ b/drivers/net/ethernet/broadcom/genet/bcmgenet.c
@@ -3751,8 +3751,8 @@ static const struct bcmgenet_hw_params bcmgenet_hw_params_v1 = {
 };
 
 static const struct bcmgenet_hw_params bcmgenet_hw_params_v2 = {
-	.tx_queues = 4,
-	.tx_bds_per_q = 32,
+	.tx_queues = 0,
+	.tx_bds_per_q = 0,
 	.rx_queues = 0,
 	.rx_bds_per_q = 0,
 	.bp_in_en_shift = 16,
@@ -3769,8 +3769,8 @@ static const struct bcmgenet_hw_params bcmgenet_hw_params_v2 = {
 };
 
 static const struct bcmgenet_hw_params bcmgenet_hw_params_v3 = {
-	.tx_queues = 4,
-	.tx_bds_per_q = 32,
+	.tx_queues = 0,
+	.tx_bds_per_q = 0,
 	.rx_queues = 0,
 	.rx_bds_per_q = 0,
 	.bp_in_en_shift = 17,
@@ -3787,8 +3787,8 @@ static const struct bcmgenet_hw_params bcmgenet_hw_params_v3 = {
 };
 
 static const struct bcmgenet_hw_params bcmgenet_hw_params_v4 = {
-	.tx_queues = 4,
-	.tx_bds_per_q = 32,
+	.tx_queues = 0,
+	.tx_bds_per_q = 0,
 	.rx_queues = 0,
 	.rx_bds_per_q = 0,
 	.bp_in_en_shift = 17,
-- 
2.53.0