net: dsa: microchip: Disable PTP function of KSZ8463

The PTP function of KSZ8463 is on by default.  However, its proprietary
way of storing timestamp directly in a reserved field inside the PTP
message header is not suitable for use with the current Linux PTP stack
implementation.  It is necessary to disable the PTP function to not
interfere the normal operation of the MAC.

Note the PTP driver for KSZ switches does not work for KSZ8463 and is not
activated for it.

Signed-off-by: Tristram Ha <tristram.ha@microchip.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/20250725001753.6330-7-Tristram.Ha@microchip.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: triha2work

drivers/net/dsa/microchip/ksz8.c

@@ -1760,6 +1760,17 @@ void ksz8_config_cpu_port(struct dsa_switch *ds)
 					   KSZ8463_REG_DSP_CTRL_6,
 					   COPPER_RECEIVE_ADJUSTMENT, 0);
 		}
+
+		/* Turn off PTP function as the switch's proprietary way of
+		 * handling timestamp is not supported in current Linux PTP
+		 * stack implementation.
+		 */
+		regmap_update_bits(ksz_regmap_16(dev),
+				   KSZ8463_PTP_MSG_CONF1,
+				   PTP_ENABLE, 0);
+		regmap_update_bits(ksz_regmap_16(dev),
+				   KSZ8463_PTP_CLK_CTRL,
+				   PTP_CLK_ENABLE, 0);
 	}
 }