net: phy: micrel: lan8814 cable improvement errata

When the length of the cable is more than 100m and the lan8814 is
configured to run in 1000Base-T Slave then the register of the device
needs to be optimized.

Workaround this by setting the measure time to a value of 0xb. This
value can be set regardless of the configuration.

This issue is described in 'LAN8814 Silicon Errata and Data Sheet
Clarification' and according to that, this will not be corrected in a
future silicon revision.
Reviewed-by: Wojciech Drewek <wojciech.drewek@intel.com>
Signed-off-by: Horatiu Vultur <horatiu.vultur@microchip.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Acked-by: Arun Ramadoss <arun.ramadoss@microchip.com>
Link: https://lore.kernel.org/r/20240304091548.1386022-3-horatiu.vultur@microchip.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/phy/micrel.c

@@ -117,6 +117,10 @@
 #define LAN8814_EEE_STATE			0x38
 #define LAN8814_EEE_STATE_MASK2P5P		BIT(10)
 
+#define LAN8814_PD_CONTROLS			0x9d
+#define LAN8814_PD_CONTROLS_PD_MEAS_TIME_MASK	GENMASK(3, 0)
+#define LAN8814_PD_CONTROLS_PD_MEAS_TIME_VAL	0xb
+
 /* Represents 1ppm adjustment in 2^32 format with
  * each nsec contains 4 clock cycles.
  * The value is calculated as following: (1/1000000)/((2^-32)/4)
@@ -3304,6 +3308,20 @@ static void lan8814_clear_2psp_bit(struct phy_device *phydev)
 	lanphy_write_page_reg(phydev, 2, LAN8814_EEE_STATE, val);
 }
 
+static void lan8814_update_meas_time(struct phy_device *phydev)
+{
+	u16 val;
+
+	/* By setting the measure time to a value of 0xb this will allow cables
+	 * longer than 100m to be used. This configuration can be used
+	 * regardless of the mode of operation of the PHY
+	 */
+	val = lanphy_read_page_reg(phydev, 1, LAN8814_PD_CONTROLS);
+	val &= ~LAN8814_PD_CONTROLS_PD_MEAS_TIME_MASK;
+	val |= LAN8814_PD_CONTROLS_PD_MEAS_TIME_VAL;
+	lanphy_write_page_reg(phydev, 1, LAN8814_PD_CONTROLS, val);
+}
+
 static int lan8814_probe(struct phy_device *phydev)
 {
 	const struct kszphy_type *type = phydev->drv->driver_data;
@@ -3342,6 +3360,7 @@ static int lan8814_probe(struct phy_device *phydev)
 
 	/* Errata workarounds */
 	lan8814_clear_2psp_bit(phydev);
+	lan8814_update_meas_time(phydev);
 
 	return 0;
 }