net: gem: Fix setting PCS auto-negotiation state

The code was trying to disable PCS auto-negotiation when a fixed-link node
is present and enable it otherwise. However, the PCS registers were being
written before the PCSSEL bit was set in the network configuration
register, and it appears that in this state, PCS register writes are
ignored. The result is that the intended change only took effect on the
second network operation that was performed, since at that time PCSSEL is
already enabled.

Fix the order of register writes so that PCS registers are only written to
after the PCS is enabled.

Fixes: 26e62cc9 ("net: gem: Disable PCS autonegotiation in case of fixed-link")
Signed-off-by: Robert Hancock <robert.hancock@calian.com>
Reviewed-by: Ramon Fried <rfried.dev@gmail.com>
Reviewed-by: Ashok Reddy Soma <ashok.reddy.soma@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>

drivers/net/zynq_gem.c

@@ -454,14 +454,6 @@ static int zynq_gem_init(struct udevice *dev)
 	    priv->int_pcs) {
 		nwconfig |= ZYNQ_GEM_NWCFG_SGMII_ENBL |
 			    ZYNQ_GEM_NWCFG_PCS_SEL;
-#ifdef CONFIG_ARM64
-	if (priv->phydev->phy_id != PHY_FIXED_ID)
-		writel(readl(&regs->pcscntrl) | ZYNQ_GEM_PCS_CTL_ANEG_ENBL,
-		       &regs->pcscntrl);
-	else
-		writel(readl(&regs->pcscntrl) & ~ZYNQ_GEM_PCS_CTL_ANEG_ENBL,
-		       &regs->pcscntrl);
-#endif
 	}
 
 	switch (priv->phydev->speed) {
@@ -480,6 +472,23 @@ static int zynq_gem_init(struct udevice *dev)
 		break;
 	}
 
+#ifdef CONFIG_ARM64
+	if (priv->interface == PHY_INTERFACE_MODE_SGMII &&
+	    priv->int_pcs) {
+		/*
+		 * Disable AN for fixed link configuration, enable otherwise.
+		 * Must be written after PCS_SEL is set in nwconfig,
+		 * otherwise writes will not take effect.
+		 */
+		if (priv->phydev->phy_id != PHY_FIXED_ID)
+			writel(readl(&regs->pcscntrl) | ZYNQ_GEM_PCS_CTL_ANEG_ENBL,
+			       &regs->pcscntrl);
+		else
+			writel(readl(&regs->pcscntrl) & ~ZYNQ_GEM_PCS_CTL_ANEG_ENBL,
+			       &regs->pcscntrl);
+	}
+#endif
+
 	ret = clk_set_rate(&priv->tx_clk, clk_rate);
 	if (IS_ERR_VALUE(ret)) {
 		dev_err(dev, "failed to set tx clock rate\n");