phy: armada-38x: fix NETA lockup when repeatedly switching speeds

The mvneta hardware appears to lock up in various random ways when
repeatedly switching speeds between 1G and 2.5G, which involves
reprogramming the COMPHY.  It is not entirely clear why this happens,
but best guess is that reprogramming the COMPHY glitches mvneta clocks
causing the hardware to fail.  It seems that rebooting resolves the
failure, but not down/up cycling the interface alone.

Various other approaches have been tried, such as trying to cleanly
power down the COMPHY and then take it back through the power up
initialisation, but this does not seem to help.

It was finally noticed that u-boot's last step when configuring a
COMPHY for "SGMII" mode was to poke at a register described as
"GBE_CONFIGURATION_REG", which is undocumented in any external
documentation.  All that we have is the fact that u-boot sets a bit
corresponding to the "SGMII" lane at the end of COMPHY initialisation.

Experimentation shows that if we clear this bit prior to changing the
speed, and then set it afterwards, mvneta does not suffer this problem
on the SolidRun Clearfog when switching speeds between 1G and 2.5G.

This problem was found while script-testing phylink.

This fix also requires the corresponding change to DT to be effective.
See "ARM: dts: armada-38x: fix NETA lockup when repeatedly switching
speeds".

Fixes: 14dc100b ("phy: armada38x: add common phy support")
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lore.kernel.org/r/E1jxtRj-0003Tz-CG@rmk-PC.armlinux.org.ukSigned-off-by: Vinod Koul <vkoul@kernel.org>

drivers/phy/marvell/phy-armada38x-comphy.c

@@ -41,6 +41,7 @@ struct a38x_comphy_lane {
 
 struct a38x_comphy {
 	void __iomem *base;
+	void __iomem *conf;
 	struct device *dev;
 	struct a38x_comphy_lane lane[MAX_A38X_COMPHY];
 };
@@ -54,6 +55,21 @@ static const u8 gbe_mux[MAX_A38X_COMPHY][MAX_A38X_PORTS] = {
 	{ 0, 0, 3 },
 };
 
+static void a38x_set_conf(struct a38x_comphy_lane *lane, bool enable)
+{
+	struct a38x_comphy *priv = lane->priv;
+	u32 conf;
+
+	if (priv->conf) {
+		conf = readl_relaxed(priv->conf);
+		if (enable)
+			conf |= BIT(lane->port);
+		else
+			conf &= ~BIT(lane->port);
+		writel(conf, priv->conf);
+	}
+}
+
 static void a38x_comphy_set_reg(struct a38x_comphy_lane *lane,
 				unsigned int offset, u32 mask, u32 value)
 {
@@ -97,6 +113,7 @@ static int a38x_comphy_set_mode(struct phy *phy, enum phy_mode mode, int sub)
 {
 	struct a38x_comphy_lane *lane = phy_get_drvdata(phy);
 	unsigned int gen;
+	int ret;
 
 	if (mode != PHY_MODE_ETHERNET)
 		return -EINVAL;
@@ -115,13 +132,20 @@ static int a38x_comphy_set_mode(struct phy *phy, enum phy_mode mode, int sub)
 		return -EINVAL;
 	}
 
+	a38x_set_conf(lane, false);
+
 	a38x_comphy_set_speed(lane, gen, gen);
 
-	return a38x_comphy_poll(lane, COMPHY_STAT1,
-				COMPHY_STAT1_PLL_RDY_TX |
-				COMPHY_STAT1_PLL_RDY_RX,
-				COMPHY_STAT1_PLL_RDY_TX |
-				COMPHY_STAT1_PLL_RDY_RX);
+	ret = a38x_comphy_poll(lane, COMPHY_STAT1,
+			       COMPHY_STAT1_PLL_RDY_TX |
+			       COMPHY_STAT1_PLL_RDY_RX,
+			       COMPHY_STAT1_PLL_RDY_TX |
+			       COMPHY_STAT1_PLL_RDY_RX);
+
+	if (ret == 0)
+		a38x_set_conf(lane, true);
+
+	return ret;
 }
 
 static const struct phy_ops a38x_comphy_ops = {
@@ -174,14 +198,21 @@ static int a38x_comphy_probe(struct platform_device *pdev)
 	if (!priv)
 		return -ENOMEM;
 
-	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
-	base = devm_ioremap_resource(&pdev->dev, res);
+	base = devm_platform_ioremap_resource(pdev, 0);
 	if (IS_ERR(base))
 		return PTR_ERR(base);
 
 	priv->dev = &pdev->dev;
 	priv->base = base;
 
+	/* Optional */
+	res = platform_get_resource_byname(pdev, IORESOURCE_MEM, "conf");
+	if (res) {
+		priv->conf = devm_ioremap_resource(&pdev->dev, res);
+		if (IS_ERR(priv->conf))
+			return PTR_ERR(priv->conf);
+	}
+
 	for_each_available_child_of_node(pdev->dev.of_node, child) {
 		struct phy *phy;
 		int ret;