at803x: fix suspend/resume for SGMII link

When operating the at803x in SGMII mode, resuming the chip
from power down brings up the copper-side link but leaves
the SGMII link in unconnected state (tested with at8031
attached to gianfar). In effect, this caused a permanent
link loss once the related interface was put down.

This patch ensures that power down handling in supspend()
and resume() is also applied to the SGMII link.

Signed-off-by: Zefir Kurtisi <zefir.kurtisi@neratec.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/phy/at803x.c

@@ -52,6 +52,9 @@
 #define AT803X_DEBUG_REG_5			0x05
 #define AT803X_DEBUG_TX_CLK_DLY_EN		BIT(8)
 
+#define AT803X_REG_CHIP_CONFIG			0x1f
+#define AT803X_BT_BX_REG_SEL			0x8000
+
 #define ATH8030_PHY_ID 0x004dd076
 #define ATH8031_PHY_ID 0x004dd074
 #define ATH8035_PHY_ID 0x004dd072
@@ -206,6 +209,7 @@ static int at803x_suspend(struct phy_device *phydev)
 {
 	int value;
 	int wol_enabled;
+	int ccr;
 
 	mutex_lock(&phydev->lock);
 
@@ -221,6 +225,16 @@ static int at803x_suspend(struct phy_device *phydev)
 
 	phy_write(phydev, MII_BMCR, value);
 
+	if (phydev->interface != PHY_INTERFACE_MODE_SGMII)
+		goto done;
+
+	/* also power-down SGMII interface */
+	ccr = phy_read(phydev, AT803X_REG_CHIP_CONFIG);
+	phy_write(phydev, AT803X_REG_CHIP_CONFIG, ccr & ~AT803X_BT_BX_REG_SEL);
+	phy_write(phydev, MII_BMCR, phy_read(phydev, MII_BMCR) | BMCR_PDOWN);
+	phy_write(phydev, AT803X_REG_CHIP_CONFIG, ccr | AT803X_BT_BX_REG_SEL);
+
+done:
 	mutex_unlock(&phydev->lock);
 
 	return 0;
@@ -229,6 +243,7 @@ static int at803x_suspend(struct phy_device *phydev)
 static int at803x_resume(struct phy_device *phydev)
 {
 	int value;
+	int ccr;
 
 	mutex_lock(&phydev->lock);
 
@@ -236,6 +251,17 @@ static int at803x_resume(struct phy_device *phydev)
 	value &= ~(BMCR_PDOWN | BMCR_ISOLATE);
 	phy_write(phydev, MII_BMCR, value);
 
+	if (phydev->interface != PHY_INTERFACE_MODE_SGMII)
+		goto done;
+
+	/* also power-up SGMII interface */
+	ccr = phy_read(phydev, AT803X_REG_CHIP_CONFIG);
+	phy_write(phydev, AT803X_REG_CHIP_CONFIG, ccr & ~AT803X_BT_BX_REG_SEL);
+	value = phy_read(phydev, MII_BMCR) & ~(BMCR_PDOWN | BMCR_ISOLATE);
+	phy_write(phydev, MII_BMCR, value);
+	phy_write(phydev, AT803X_REG_CHIP_CONFIG, ccr | AT803X_BT_BX_REG_SEL);
+
+done:
 	mutex_unlock(&phydev->lock);
 
 	return 0;