net: phy: micrel: center FLP burst timing at 16ms

Like [1], reset the FLP burst timing for the KSZ9031 to the 16ms
specified by the IEEE802.3 standard from the chip's default of 8ms.

For more details, see the "Auto-Negotiation Timing" section of the
KSZ9031RNX datasheet.

[1] https://patchwork.kernel.org/patch/6558371/Signed-off-by: NAsh Charles <ash.charles@savoirfairelinux.com>
Acked-by: NJoe Hershberger <joe.hershberger@ni.com>

drivers/net/phy/micrel.c

@@ -415,11 +415,31 @@ static int ksz9031_of_config(struct phy_device *phydev)
 
 	return 0;
 }
+
+static int ksz9031_center_flp_timing(struct phy_device *phydev)
+{
+	struct phy_driver *drv = phydev->drv;
+	int ret = 0;
+
+	if (!drv || !drv->writeext)
+		return -EOPNOTSUPP;
+
+	ret = drv->writeext(phydev, 0, 0, MII_KSZ9031_FLP_BURST_TX_LO, 0x1A80);
+	if (ret)
+		return ret;
+
+	ret = drv->writeext(phydev, 0, 0, MII_KSZ9031_FLP_BURST_TX_HI, 0x6);
+	return ret;
+}
 #else
 static int ksz9031_of_config(struct phy_device *phydev)
 {
 	return 0;
 }
+static int ksz9031_center_flp_timing(struct phy_device *phydev)
+{
+	return 0;
+}
 #endif
 
 /* Accessors to extended registers*/
@@ -470,6 +490,9 @@ static int ksz9031_config(struct phy_device *phydev)
 {
 	int ret;
 	ret = ksz9031_of_config(phydev);
+	if (ret)
+		return ret;
+	ret = ksz9031_center_flp_timing(phydev);
 	if (ret)
 		return ret;
 	return genphy_config(phydev);

include/micrel.h

@@ -20,6 +20,9 @@
 #define MII_KSZ9031_EXT_RGMII_TX_DATA_SKEW	0x6
 #define MII_KSZ9031_EXT_RGMII_CLOCK_SKEW	0x8
 
+#define MII_KSZ9031_FLP_BURST_TX_LO		0x3
+#define MII_KSZ9031_FLP_BURST_TX_HI		0x4
+
 /* Registers */
 #define MMD_ACCESS_CONTROL	0xd
 #define MMD_ACCESS_REG_DATA	0xe