net: phy: mediatek: do not report link and per-speed LED rules together

mtk_phy_led_hw_ctrl_get() reports TRIGGER_NETDEV_LINK whenever any of the speed bits in on_set is on, and in addition reports every individual TRIGGER_NETDEV_LINK_* bit that is set. The netdev trigger refuses that
combination: netdev_led_attr_store() rejects TRIGGER_NETDEV_LINK together with any per-speed rule, and it validates the whole resulting mode rather than just the bit being written. Once the hardware has any link bit programmed, every write to the trigger attributes of that LED therefore fails with -EINVAL and the LED can no longer be configured.

The rules are also fed back into the hardware: the trigger stores what is read back, and a later write of device_name programs it again, expanding TRIGGER_NETDEV_LINK to every speed in on_set. An LED configured for a single speed is thereby silently widened to "on at any link speed".

Both are easy to see on the EcoNet EN7528, whose four PHYs share one LED block. The first LED programs the block correctly, the second reads those rules back and rewrites them widened, and the remaining two then read the widened value, so an LED configured for "link_10 link_100" ends up lit on a 1000 Mbps link.

on_set holds every speed the LED can indicate and is exactly what mtk_phy_led_hw_ctrl_set() programs for TRIGGER_NETDEV_LINK, so report the speed independent rule only when all of them are on, and the individual speeds otherwise. The mapping is then the inverse of the one used when programming the LED and round trips without changing the register.

---
 drivers/net/phy/mediatek/mtk-phy-lib.c | 27 ++++++++++++++++----------
 1 file changed, 17 insertions(+), 10 deletions(-)

index dfd0f4e439a2..608072fbfde9 100644
@@ -156,20 +156,27 @@ int mtk_phy_led_hw_ctrl_get(struct phy_device *phydev, u8 index,
 	if (!rules)
 		return 0;
 
-	if (on & on_set)
+	/* TRIGGER_NETDEV_LINK must not be reported together with any of the
+	 * per-speed rules, the netdev trigger rejects that combination.
+	 * on_set holds every speed this LED can indicate and is what
+	 * mtk_phy_led_hw_ctrl_set() programs for TRIGGER_NETDEV_LINK, so
+	 * report the speed independent rule only when they are all on.
+	 */
+	if ((on & on_set) == on_set) {
 		*rules |= BIT(TRIGGER_NETDEV_LINK);
+	} else {
+		if (on & MTK_PHY_LED_ON_LINK10)
+			*rules |= BIT(TRIGGER_NETDEV_LINK_10);
 
-	if (on & MTK_PHY_LED_ON_LINK10)
-		*rules |= BIT(TRIGGER_NETDEV_LINK_10);
+		if (on & MTK_PHY_LED_ON_LINK100)
+			*rules |= BIT(TRIGGER_NETDEV_LINK_100);
 
-	if (on & MTK_PHY_LED_ON_LINK100)
-		*rules |= BIT(TRIGGER_NETDEV_LINK_100);
+		if (on & MTK_PHY_LED_ON_LINK1000)
+			*rules |= BIT(TRIGGER_NETDEV_LINK_1000);
 
-	if (on & MTK_PHY_LED_ON_LINK1000)
-		*rules |= BIT(TRIGGER_NETDEV_LINK_1000);
-
-	if (on & MTK_PHY_LED_ON_LINK2500)
-		*rules |= BIT(TRIGGER_NETDEV_LINK_2500);
+		if (on & MTK_PHY_LED_ON_LINK2500)
+			*rules |= BIT(TRIGGER_NETDEV_LINK_2500);
+	}
 
 	if (on & MTK_PHY_LED_ON_FDX)
 		*rules |= BIT(TRIGGER_NETDEV_FULL_DUPLEX);

base-commit: 78445023439506ebd83b86d40b1e428a3b309d4a

2.34.1

Andrew