net: phy: at803x: generalize cdt fault length function

Generalize cable test fault length function since they all base on the
same magic values (already reverse engineered to understand the meaning
of it) to have consistenct values on every PHY.
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/phy/at803x.c

@@ -1192,10 +1192,8 @@ static bool at803x_cdt_fault_length_valid(u16 status)
 	return false;
 }
 
-static int at803x_cdt_fault_length(u16 status)
+static int at803x_cdt_fault_length(int dt)
 {
-	int dt;
-
 	/* According to the datasheet the distance to the fault is
 	 * DELTA_TIME * 0.824 meters.
 	 *
@@ -1211,8 +1209,6 @@ static int at803x_cdt_fault_length(u16 status)
 	 * With a VF of 0.69 we get the factor 0.824 mentioned in the
 	 * datasheet.
 	 */
-	dt = FIELD_GET(AT803X_CDT_STATUS_DELTA_TIME_MASK, status);
-
 	return (dt * 824) / 10;
 }
 
@@ -1265,9 +1261,11 @@ static int at803x_cable_test_one_pair(struct phy_device *phydev, int pair)
 	ethnl_cable_test_result(phydev, ethtool_pair[pair],
 				at803x_cable_test_result_trans(val));
 
-	if (at803x_cdt_fault_length_valid(val))
+	if (at803x_cdt_fault_length_valid(val)) {
+		val = FIELD_GET(AT803X_CDT_STATUS_DELTA_TIME_MASK, val);
 		ethnl_cable_test_fault_length(phydev, ethtool_pair[pair],
 					      at803x_cdt_fault_length(val));
+	}
 
 	return 1;
 }
@@ -1992,7 +1990,8 @@ static int qca808x_cdt_fault_length(struct phy_device *phydev, int pair)
 	if (val < 0)
 		return val;
 
-	return (FIELD_GET(QCA808X_CDT_DIAG_LENGTH, val) * 824) / 10;
+	val = FIELD_GET(QCA808X_CDT_DIAG_LENGTH, val);
+	return at803x_cdt_fault_length(val);
 }
 
 static int qca808x_cable_test_start(struct phy_device *phydev)