net: phy: fix EEE advertisement not restored after eee off/on toggle

When EEE is disabled via 'ethtool --set-eee eth0 eee off' and then
re-enabled with 'ethtool --set-eee eth0 eee on' (without explicitly
specifying advertised modes), the advertised EEE link modes are lost,
showing "Not reported" instead of being restored to the supported
modes.

The bug is a state ordering issue in phy_ethtool_set_eee():

  genphy_c45_ethtool_set_eee(phydev, data);  // uses OLD eee_cfg
  eee_to_eeecfg(&phydev->eee_cfg, data);     // updates eee_cfg AFTER

genphy_c45_ethtool_set_eee() correctly restores advertising_eee from
supported_eee when re-enabling, but then calls
genphy_c45_an_config_eee_aneg() which checks phydev->eee_cfg.eee_enabled
-- still false from the previous 'eee off'. This causes it to write
empty modes to the PHY, overriding the just-restored advertisement.

Fix by updating eee_cfg.eee_enabled before calling
genphy_c45_ethtool_set_eee(), and restoring it on error.

Fixes: 49168d1 ("net: phy: Add phy_support_eee library function")
Signed-off-by: Nicolai Buchwitz <nb@tipi-net.de>

Author: nbuchwitz

drivers/net/phy/phy.c

@@ -1763,17 +1763,30 @@ static void phy_ethtool_set_eee_noneg(struct phy_device *phydev,
  */
 int phy_ethtool_set_eee(struct phy_device *phydev, struct ethtool_keee *data)
 {
+	bool old_eee_enabled;
 	int ret;
 
 	if (!phydev->drv)
 		return -EIO;
 
 	mutex_lock(&phydev->lock);
+	/* Update eee_enabled before calling genphy_c45_ethtool_set_eee(),
+	 * because it calls genphy_c45_an_config_eee_aneg() which reads
+	 * phydev->eee_cfg.eee_enabled to decide whether to write the
+	 * advertisement to the PHY. Without this, toggling EEE off then
+	 * on results in empty advertisement (the old eee_enabled=false
+	 * causes it to write zero modes despite advertising_eee being
+	 * correctly restored).
+	 */
+	old_eee_enabled = phydev->eee_cfg.eee_enabled;
+	phydev->eee_cfg.eee_enabled = data->eee_enabled;
 	ret = genphy_c45_ethtool_set_eee(phydev, data);
 	if (ret >= 0) {
 		if (ret == 0)
 			phy_ethtool_set_eee_noneg(phydev, data);
 		eee_to_eeecfg(&phydev->eee_cfg, data);
+	} else {
+		phydev->eee_cfg.eee_enabled = old_eee_enabled;
 	}
 	mutex_unlock(&phydev->lock);