+static int lan88xx_set_downshift(struct phy_device *phydev, u8 cnt)
+{
+	u32 mask = LAN78XX_PHY_CTRL3_DOWNSHIFT_CTRL_MASK |
+		   LAN78XX_PHY_CTRL3_AUTO_DOWNSHIFT;
+	u32 val;
+
+	if (cnt == DOWNSHIFT_DEV_DISABLE)
+		return phy_modify_paged(phydev, 1, LAN78XX_PHY_CTRL3,
+					LAN78XX_PHY_CTRL3_AUTO_DOWNSHIFT, 0);
+
+	if (cnt == DOWNSHIFT_DEV_DEFAULT_COUNT)
+		cnt = 2;
+
+	switch (cnt) {
+	case 2:
+		val = LAN78XX_PHY_CTRL3_DOWNSHIFT_CTRL_2;
+		break;
+	case 3:
+		val = LAN78XX_PHY_CTRL3_DOWNSHIFT_CTRL_3;
+		break;
+	case 4:
+		val = LAN78XX_PHY_CTRL3_DOWNSHIFT_CTRL_4;
+		break;
+	case 5:
+		val = LAN78XX_PHY_CTRL3_DOWNSHIFT_CTRL_5;
+		break;
+	default:
+		return -EINVAL;

And this could be a range check followed by a FIELD_PREP(cnt - 2);

	Andrew