net: phy: dp83867: retrigger SGMII AN when link change

There is a limitation in TI DP83867 PHY device where SGMII AN is only
triggered once after the device is booted up. Even after the PHY TPI is
down and up again, SGMII AN is not triggered and hence no new in-band
message from PHY to MAC side SGMII.

This could cause an issue during power up, when PHY is up prior to MAC.
At this condition, once MAC side SGMII is up, MAC side SGMII wouldn`t
receive new in-band message from TI PHY with correct link status, speed
and duplex info.

As suggested by TI, implemented a SW solution here to retrigger SGMII
Auto-Neg whenever there is a link change.

v2: Add Fixes tag in commit message.

Fixes: 2a10154a ("net: phy: dp83867: Add TI dp83867 phy")
Cc: <stable@vger.kernel.org> # 5.4.x
Signed-off-by: Sit, Michael Wei Hong <michael.wei.hong.sit@intel.com>
Reviewed-by: Voon Weifeng <weifeng.voon@intel.com>
Signed-off-by: Tan Tee Min <tee.min.tan@linux.intel.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lore.kernel.org/r/20220526090347.128742-1-tee.min.tan@linux.intel.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/phy/dp83867.c

@@ -137,6 +137,7 @@
 #define DP83867_DOWNSHIFT_2_COUNT	2
 #define DP83867_DOWNSHIFT_4_COUNT	4
 #define DP83867_DOWNSHIFT_8_COUNT	8
+#define DP83867_SGMII_AUTONEG_EN	BIT(7)
 
 /* CFG3 bits */
 #define DP83867_CFG3_INT_OE			BIT(7)
@@ -855,6 +856,32 @@ static int dp83867_phy_reset(struct phy_device *phydev)
 			 DP83867_PHYCR_FORCE_LINK_GOOD, 0);
 }
 
+static void dp83867_link_change_notify(struct phy_device *phydev)
+{
+	/* There is a limitation in DP83867 PHY device where SGMII AN is
+	 * only triggered once after the device is booted up. Even after the
+	 * PHY TPI is down and up again, SGMII AN is not triggered and
+	 * hence no new in-band message from PHY to MAC side SGMII.
+	 * This could cause an issue during power up, when PHY is up prior
+	 * to MAC. At this condition, once MAC side SGMII is up, MAC side
+	 * SGMII wouldn`t receive new in-band message from TI PHY with
+	 * correct link status, speed and duplex info.
+	 * Thus, implemented a SW solution here to retrigger SGMII Auto-Neg
+	 * whenever there is a link change.
+	 */
+	if (phydev->interface == PHY_INTERFACE_MODE_SGMII) {
+		int val = 0;
+
+		val = phy_clear_bits(phydev, DP83867_CFG2,
+				     DP83867_SGMII_AUTONEG_EN);
+		if (val < 0)
+			return;
+
+		phy_set_bits(phydev, DP83867_CFG2,
+			     DP83867_SGMII_AUTONEG_EN);
+	}
+}
+
 static struct phy_driver dp83867_driver[] = {
 	{
 		.phy_id		= DP83867_PHY_ID,
@@ -879,6 +906,8 @@ static struct phy_driver dp83867_driver[] = {
 
 		.suspend	= genphy_suspend,
 		.resume		= genphy_resume,
+
+		.link_change_notify = dp83867_link_change_notify,
 	},
 };
 module_phy_driver(dp83867_driver);