net: phy: Micrel KSZ8061: fix errata solution not taking effect problem

KSZ8061 needs to write to a MMD register at driver initialization to fix
an errata. This worked in 5.0 kernel but not in newer kernels. The
issue is the main phylib code no longer resets PHY at the very beginning.
Calling phy resuming code later will reset the chip if it is already
powered down at the beginning. This wipes out the MMD register write.
Solution is to implement a phy resume function for KSZ8061 to take care
of this problem.

Fixes: 232ba3a51cc2 ("net: phy: Micrel KSZ8061: link failure after cable connect")
Signed-off-by: Tristram Ha <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/net/phy/micrel.c

···
 {
 	int ret;
 
+	/* Chip can be powered down by the bootstrap code. */
+	ret = phy_read(phydev, MII_BMCR);
+	if (ret < 0)
+		return ret;
+	if (ret & BMCR_PDOWN) {
+		ret = phy_write(phydev, MII_BMCR, ret & ~BMCR_PDOWN);
+		if (ret < 0)
+			return ret;
+		usleep_range(1000, 2000);
+	}
+
 	ret = phy_write_mmd(phydev, MDIO_MMD_PMAPMD, MDIO_DEVID1, 0xB61A);
 	if (ret)
 		return ret;
···
 		if (ret)
 			return ret;
 	}
+
+	/* Enable PHY Interrupts */
+	if (phy_interrupt_is_valid(phydev)) {
+		phydev->interrupts = PHY_INTERRUPT_ENABLED;
+		if (phydev->drv->config_intr)
+			phydev->drv->config_intr(phydev);
+	}
+
+	return 0;
+}
+
+static int ksz8061_resume(struct phy_device *phydev)
+{
+	int ret;
+
+	/* This function can be called twice when the Ethernet device is on. */
+	ret = phy_read(phydev, MII_BMCR);
+	if (ret < 0)
+		return ret;
+	if (!(ret & BMCR_PDOWN))
+		return 0;
+
+	genphy_resume(phydev);
+	usleep_range(1000, 2000);
+
+	/* Re-program the value after chip is reset. */
+	ret = phy_write_mmd(phydev, MDIO_MMD_PMAPMD, MDIO_DEVID1, 0xB61A);
+	if (ret)
+		return ret;
 
 	/* Enable PHY Interrupts */
 	if (phy_interrupt_is_valid(phydev)) {
···
 	.config_intr	= kszphy_config_intr,
 	.handle_interrupt = kszphy_handle_interrupt,
 	.suspend	= kszphy_suspend,
-	.resume		= kszphy_resume,
+	.resume		= ksz8061_resume,
 }, {
 	.phy_id		= PHY_ID_KSZ9021,
 	.phy_id_mask	= 0x000ffffe,