[net v5 PATCH] net: stmmac: replace priv->speed with the portTransmitRate from the tc-cbs parameters

[Xiaolei Wang]

The current cbs parameter depends on speed after uplinking,
which is not needed and will report a configuration error
if the port is not initially connected. The UAPI exposed by
tc-cbs requires userspace to recalculate the send slope anyway,
because the formula depends on port_transmit_rate (see man tc-cbs),
which is not an invariant from tc's perspective. Therefore, we
use offload->sendslope and offload->idleslope to derive the
original port_transmit_rate from the CBS formula.

Fixes: 1f705bc61aee ("net: stmmac: Add support for CBS QDISC")
Signed-off-by: Xiaolei Wang <xiaolei.wang at windriver.com>
Reviewed-by: Wojciech Drewek <wojciech.drewek at intel.com>
---

Change log:

v1:
    https://patchwork.kernel.org/project/linux-arm-kernel/patch/20240528092010.439089-1-xiaolei.wang@windriver.com/
v2:
    Update CBS parameters when speed changes after linking up
    https://patchwork.kernel.org/project/linux-arm-kernel/patch/20240530061453.561708-1-xiaolei.wang@windriver.com/
v3:
    replace priv->speed with the  portTransmitRate from the tc-cbs parameters suggested by Vladimir Oltean
    link: https://patchwork.kernel.org/project/linux-arm-kernel/patch/20240607103327.438455-1-xiaolei.wang@windriver.com/
v4:
    Delete speed_div variable, delete redundant port_transmit_rate_kbps = qopt->idleslope - qopt->sendslope; and update commit log
    https://patchwork.kernel.org/project/linux-arm-kernel/patch/20240608044557.1380550-1-xiaolei.wang@windriver.com/
v5:
    use reverse Christmas tree (RCT) variable ordering and If the portTransmitRate(idleSlope - sendSlope) parameter is invalid, add an error output to avoid user misunderstanding 

 .../net/ethernet/stmicro/stmmac/stmmac_tc.c   | 25 ++++++++-----------
 1 file changed, 11 insertions(+), 14 deletions(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_tc.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_tc.c
index 222540b55480..1562fbdd0a04 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_tc.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_tc.c
@@ -343,10 +343,11 @@ static int tc_setup_cbs(struct stmmac_priv *priv,
 			struct tc_cbs_qopt_offload *qopt)
 {
 	u32 tx_queues_count = priv->plat->tx_queues_to_use;
+	s64 port_transmit_rate_kbps;
 	u32 queue = qopt->queue;
-	u32 ptr, speed_div;
 	u32 mode_to_use;
 	u64 value;
+	u32 ptr;
 	int ret;
 
 	/* Queue 0 is not AVB capable */
@@ -355,30 +356,26 @@ static int tc_setup_cbs(struct stmmac_priv *priv,
 	if (!priv->dma_cap.av)
 		return -EOPNOTSUPP;
 
+	port_transmit_rate_kbps = qopt->idleslope - qopt->sendslope;
+
 	/* Port Transmit Rate and Speed Divider */
-	switch (priv->speed) {
+	switch (div_s64(port_transmit_rate_kbps, 1000)) {
 	case SPEED_10000:
-		ptr = 32;
-		speed_div = 10000000;
-		break;
 	case SPEED_5000:
 		ptr = 32;
-		speed_div = 5000000;
 		break;
 	case SPEED_2500:
-		ptr = 8;
-		speed_div = 2500000;
-		break;
 	case SPEED_1000:
 		ptr = 8;
-		speed_div = 1000000;
 		break;
 	case SPEED_100:
 		ptr = 4;
-		speed_div = 100000;
 		break;
 	default:
-		return -EOPNOTSUPP;
+		netdev_err(priv->dev,
+			   "Invalid portTransmitRate %lld (idleSlope - sendSlope)\n",
+			   port_transmit_rate_kbps);
+		return -EINVAL;
 	}
 
 	mode_to_use = priv->plat->tx_queues_cfg[queue].mode_to_use;
@@ -398,10 +395,10 @@ static int tc_setup_cbs(struct stmmac_priv *priv,
 	}
 
 	/* Final adjustments for HW */
-	value = div_s64(qopt->idleslope * 1024ll * ptr, speed_div);
+	value = div_s64(qopt->idleslope * 1024ll * ptr, port_transmit_rate_kbps);
 	priv->plat->tx_queues_cfg[queue].idle_slope = value & GENMASK(31, 0);
 
-	value = div_s64(-qopt->sendslope * 1024ll * ptr, speed_div);
+	value = div_s64(-qopt->sendslope * 1024ll * ptr, port_transmit_rate_kbps);
 	priv->plat->tx_queues_cfg[queue].send_slope = value & GENMASK(31, 0);
 
 	value = qopt->hicredit * 1024ll * 8;
-- 
2.25.1