[PATCH net v2 1/1] net: stmmac: Fix zero-division error when disabling tc cbs

[KhaiWenTan]

The commit b8c43360f6e4 ("net: stmmac: No need to calculate speed divider
when offload is disabled") allows the "port_transmit_rate_kbps" to be
set to a value of 0, which is then passed to the "div_s64" function when
tc-cbs is disabled. This leads to a zero-division error.

When tc-cbs is disabled, the idleslope, sendslope, and credit values the
credit values are not required to be configured. Therefore, adding a return
statement after setting the txQ mode to DCB when tc-cbs is disabled would
prevent a zero-division error.

Fixes: b8c43360f6e4 ("net: stmmac: No need to calculate speed divider when offload is disabled")
Cc: <stable@xxxxxxxxxxxxxxx>
Co-developed-by: Choong Yong Liang <yong.liang.choong@xxxxxxxxxxxxxxx>
Signed-off-by: Choong Yong Liang <yong.liang.choong@xxxxxxxxxxxxxxx>
Signed-off-by: KhaiWenTan <khai.wen.tan@xxxxxxxxxxxxxxx>
---
v2:
  - reflected code for better understanding
v1: https://patchwork.kernel.org/project/netdevbpf/patch/20240912015541.363600-1-khai.wen.tan@xxxxxxxxxxxxxxx/
---
 drivers/net/ethernet/stmicro/stmmac/stmmac_tc.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_tc.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_tc.c
index 832998bc020b..75ad2da1a37f 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_tc.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_tc.c
@@ -386,6 +386,7 @@ static int tc_setup_cbs(struct stmmac_priv *priv,
 			return ret;
 
 		priv->plat->tx_queues_cfg[queue].mode_to_use = MTL_QUEUE_DCB;
+		return 0;
 	}
 
 	/* Final adjustments for HW */
-- 
2.25.1