net: phy: Fix "link partner" information disappear issue

Some drivers just call phy_ethtool_ksettings_set() to set the
links, for those phy drivers that use genphy_read_status(), if
autoneg is on, and the link is up, than execute "ethtool -s
ethx autoneg on" will cause "link partner" information disappear.

The call trace is phy_ethtool_ksettings_set()->phy_start_aneg()
->linkmode_zero(phydev->lp_advertising)->genphy_read_status(),
the link didn't change, so genphy_read_status() just return, and
phydev->lp_advertising is zero now.

This patch moves the clear operation of lp_advertising from
phy_start_aneg() to genphy_read_lpa()/genphy_c45_read_lpa(), and
if autoneg on and autoneg not complete, just clear what the
generic functions care about.

Fixes: 88d6272a ("net: phy: avoid unneeded MDIO reads in genphy_read_status")
Signed-off-by: Yonglong Liu <liuyonglong@huawei.com>
Reviewed-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/phy/phy-c45.c

@@ -323,6 +323,8 @@ int genphy_c45_read_pma(struct phy_device *phydev)
 {
 	int val;
 
+	linkmode_zero(phydev->lp_advertising);
+
 	val = phy_read_mmd(phydev, MDIO_MMD_PMAPMD, MDIO_CTRL1);
 	if (val < 0)
 		return val;

drivers/net/phy/phy.c

@@ -572,9 +572,6 @@ int phy_start_aneg(struct phy_device *phydev)
 	if (AUTONEG_DISABLE == phydev->autoneg)
 		phy_sanitize_settings(phydev);
 
-	/* Invalidate LP advertising flags */
-	linkmode_zero(phydev->lp_advertising);
-
 	err = phy_config_aneg(phydev);
 	if (err < 0)
 		goto out_unlock;

drivers/net/phy/phy_device.c

@@ -1787,7 +1787,14 @@ int genphy_read_lpa(struct phy_device *phydev)
 {
 	int lpa, lpagb;
 
-	if (phydev->autoneg == AUTONEG_ENABLE && phydev->autoneg_complete) {
+	if (phydev->autoneg == AUTONEG_ENABLE) {
+		if (!phydev->autoneg_complete) {
+			mii_stat1000_mod_linkmode_lpa_t(phydev->lp_advertising,
+							0);
+			mii_lpa_mod_linkmode_lpa_t(phydev->lp_advertising, 0);
+			return 0;
+		}
+
 		if (phydev->is_gigabit_capable) {
 			lpagb = phy_read(phydev, MII_STAT1000);
 			if (lpagb < 0)
@@ -1815,6 +1822,8 @@ int genphy_read_lpa(struct phy_device *phydev)
 			return lpa;
 
 		mii_lpa_mod_linkmode_lpa_t(phydev->lp_advertising, lpa);
+	} else {
+		linkmode_zero(phydev->lp_advertising);
 	}
 
 	return 0;