net: phy: micrel: ksz9131 led errata workaround

Micrel KSZ9131 PHY LED behavior is not correct when configured in
Individual Mode, LED1 (Activity LED) is in the ON state when there is
no-link.

Workaround this by setting bit 9 of register 0x1e after verifying that
the LED configuration is Individual Mode.

This issue is described in KSZ9131RNX Silicon Errata DS80000693B [*]
and according to that it will not be corrected in a future silicon
revision.

[*] https://ww1.microchip.com/downloads/en/DeviceDoc/KSZ9131RNX-Silicon-Errata-and-Data-Sheet-Clarification-80000863B.pdfSigned-off-by: Francesco Dolcini <francesco.dolcini@toradex.com>
Reviewed-by: Philippe Schenker <philippe.schenker@toradex.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/phy/micrel.c

@@ -1003,6 +1003,26 @@ static int ksz9131_config_rgmii_delay(struct phy_device *phydev)
 			      txcdll_val);
 }
 
+/* Silicon Errata DS80000693B
+ *
+ * When LEDs are configured in Individual Mode, LED1 is ON in a no-link
+ * condition. Workaround is to set register 0x1e, bit 9, this way LED1 behaves
+ * according to the datasheet (off if there is no link).
+ */
+static int ksz9131_led_errata(struct phy_device *phydev)
+{
+	int reg;
+
+	reg = phy_read_mmd(phydev, 2, 0);
+	if (reg < 0)
+		return reg;
+
+	if (!(reg & BIT(4)))
+		return 0;
+
+	return phy_set_bits(phydev, 0x1e, BIT(9));
+}
+
 static int ksz9131_config_init(struct phy_device *phydev)
 {
 	struct device_node *of_node;
@@ -1058,6 +1078,10 @@ static int ksz9131_config_init(struct phy_device *phydev)
 	if (ret < 0)
 		return ret;
 
+	ret = ksz9131_led_errata(phydev);
+	if (ret < 0)
+		return ret;
+
 	return 0;
 }