[PATCH net v2 2/2] net: macb: reject an unknown link speed in the taprio setup

[Aleksei Sviridkin <f@lex.la>]

speed is a u32, so SPEED_UNKNOWN arrives as 0xffffffff and passes the
"speed <= 0" check, which only ever catches zero. That is what an
autonegotiating link reports while it is down: the limit derived from
the speed collapses to a nanosecond at most and the first entry fails
with a misleading "exceeds hardware limit". Zero stays covered, it is
what an interface that was never opened reports, and
enst_max_hw_interval() divides by it. Say which case it was in the
error.

Fixes: 89934dbf169e ("net: macb: Add TAPRIO traffic scheduling support")
Assisted-by: LLM
Signed-off-by: Aleksei Sviridkin <f@lex.la>
---
ethtool_validate_speed() accepts SPEED_UNKNOWN (and zero), so it cannot
replace this check.

v2: error text and message per Théo Lebrun.

 drivers/net/ethernet/cadence/macb_main.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/cadence/macb_main.c b/drivers/net/ethernet/cadence/macb_main.c
index 61838084989a..202bc688978c 100644
--- a/drivers/net/ethernet/cadence/macb_main.c
+++ b/drivers/net/ethernet/cadence/macb_main.c
@@ -4324,8 +4324,8 @@ static int macb_taprio_setup_replace(struct net_device *netdev,
 	}
 
 	speed = kset.base.speed;
-	if (unlikely(speed <= 0)) {
-		netdev_err(netdev, "Invalid speed: %d\n", speed);
+	if (unlikely(speed == SPEED_UNKNOWN || !speed)) {
+		netdev_err(netdev, "Invalid speed %d, link-down?\n", speed);
 		return -EINVAL;
 	}
 
-- 
2.53.0