diff --git a/drivers/net/dsa/mv88e6xxx/ptp.c b/drivers/net/dsa/mv88e6xxx/ptp.c
index a409b8661fad..aed4a4b07f34 100644
--- a/drivers/net/dsa/mv88e6xxx/ptp.c
+++ b/drivers/net/dsa/mv88e6xxx/ptp.c
@@ -40,7 +40,7 @@ static const struct mv88e6xxx_cc_coeffs mv88e6xxx_cc_10ns_coeffs = {
 	.cc_mult_dem = 3125ULL,
 };
 
-/* Other families:
+/* Other families except MV88E6393X in internal clock mode:
  * Raw timestamps are in units of 8-ns clock periods.
  *
  * clkadj = scaled_ppm * 8*2^28 / (10^6 * 2^16)
@@ -55,6 +55,21 @@ static const struct mv88e6xxx_cc_coeffs mv88e6xxx_cc_8ns_coeffs = {
 	.cc_mult_dem = 15625ULL
 };
 
+/* Family MV88E6393X using internal clock:
+ * Raw timestamps are in units of 4-ns clock periods.
+ *
+ * clkadj = scaled_ppm * 4*2^28 / (10^6 * 2^16)
+ * simplifies to
+ * clkadj = scaled_ppm * 2^8 / 5^6
+ */
+#define MV88E6XXX_CC_4NS_SHIFT 28
+static const struct mv88e6xxx_cc_coeffs mv88e6xxx_cc_4ns_coeffs = {
+	.cc_shift = MV88E6XXX_CC_4NS_SHIFT,
+	.cc_mult = 4 << MV88E6XXX_CC_4NS_SHIFT,
+	.cc_mult_num = 1 << 8,
+	.cc_mult_dem = 15625ULL
+};
+
 #define TAI_EVENT_WORK_INTERVAL msecs_to_jiffies(100)
 
 #define cc_to_chip(cc) container_of(cc, struct mv88e6xxx_chip, tstamp_cc)
@@ -110,6 +125,8 @@ mv88e6xxx_cc_coeff_get(struct mv88e6xxx_chip *chip)
 	}
 
 	switch (period_ps) {
+	case 4000:
+		return &mv88e6xxx_cc_4ns_coeffs;
 	case 8000:
 		return &mv88e6xxx_cc_8ns_coeffs;
 	case 10000:
@@ -483,10 +500,10 @@ static u64 mv88e6xxx_ptp_clock_read(const struct cyclecounter *cc)
 	return 0;
 }
 
-/* With a 125MHz input clock, the 32-bit timestamp counter overflows in ~34.3
+/* With a 250MHz input clock, the 32-bit timestamp counter overflows in ~17.2
  * seconds; this task forces periodic reads so that we don't miss any.
  */
-#define MV88E6XXX_TAI_OVERFLOW_PERIOD (HZ * 16)
+#define MV88E6XXX_TAI_OVERFLOW_PERIOD (HZ * 8)
 static void mv88e6xxx_ptp_overflow_check(struct work_struct *work)
 {
 	struct delayed_work *dw = to_delayed_work(work);