net: phylib: do not disable autoneg for fixed speeds >= 1G

We have an increasing number of drivers that are forcing
auto-negotiation to be enabled for speeds of 1G or faster.

It would appear that auto-negotiation is mandatory for speeds above
100M. In 802.3, Annex 40C's state diagrams seems to imply that
mr_autoneg_enable (BMCR AN ENABLE) doesn't affect whether or not the
AN state machines work for 1000base-T, and some PHY datasheets (e.g.
Marvell Alaska) state that disabling mr_autoneg_enable leaves AN
enabled but forced to 1G full duplex.

Other PHY datasheets imply that BMCR AN ENABLE should not be cleared
for >= 1G.

Thus, this should be handled in phylib rather than in each driver.

Rather than erroring out, arrange to implement the Marvell Alaska
solution but in software for all PHYs: generate an appropriate
single-speed advertisement for the requested speed, and keep AN
enabled to the PHY driver. However, to avoid userspace API breakage,
continue to report to userspace that we have AN disabled.
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/phy/phy_device.c

@@ -2108,22 +2108,20 @@ EXPORT_SYMBOL(phy_reset_after_clk_enable);
 /**
  * genphy_config_advert - sanitize and advertise auto-negotiation parameters
  * @phydev: target phy_device struct
+ * @advert: auto-negotiation parameters to advertise
  *
  * Description: Writes MII_ADVERTISE with the appropriate values,
  *   after sanitizing the values to make sure we only advertise
  *   what is supported.  Returns < 0 on error, 0 if the PHY's advertisement
  *   hasn't changed, and > 0 if it has changed.
  */
-static int genphy_config_advert(struct phy_device *phydev)
+static int genphy_config_advert(struct phy_device *phydev,
+				const unsigned long *advert)
 {
 	int err, bmsr, changed = 0;
 	u32 adv;
 
-	/* Only allow advertising what this PHY supports */
-	linkmode_and(phydev->advertising, phydev->advertising,
-		     phydev->supported);
-
-	adv = linkmode_adv_to_mii_adv_t(phydev->advertising);
+	adv = linkmode_adv_to_mii_adv_t(advert);
 
 	/* Setup standard advertisement */
 	err = phy_modify_changed(phydev, MII_ADVERTISE,
@@ -2146,7 +2144,7 @@ static int genphy_config_advert(struct phy_device *phydev)
 	if (!(bmsr & BMSR_ESTATEN))
 		return changed;
 
-	adv = linkmode_adv_to_mii_ctrl1000_t(phydev->advertising);
+	adv = linkmode_adv_to_mii_ctrl1000_t(advert);
 
 	err = phy_modify_changed(phydev, MII_CTRL1000,
 				 ADVERTISE_1000FULL | ADVERTISE_1000HALF,
@@ -2370,6 +2368,9 @@ EXPORT_SYMBOL(genphy_check_and_restart_aneg);
  */
 int __genphy_config_aneg(struct phy_device *phydev, bool changed)
 {
+	__ETHTOOL_DECLARE_LINK_MODE_MASK(fixed_advert);
+	const struct phy_setting *set;
+	unsigned long *advert;
 	int err;
 
 	err = genphy_c45_an_config_eee_aneg(phydev);
@@ -2384,10 +2385,25 @@ int __genphy_config_aneg(struct phy_device *phydev, bool changed)
 	else if (err)
 		changed = true;
 
-	if (AUTONEG_ENABLE != phydev->autoneg)
+	if (phydev->autoneg == AUTONEG_ENABLE) {
+		/* Only allow advertising what this PHY supports */
+		linkmode_and(phydev->advertising, phydev->advertising,
+			     phydev->supported);
+		advert = phydev->advertising;
+	} else if (phydev->speed < SPEED_1000) {
 		return genphy_setup_forced(phydev);
+	} else {
+		linkmode_zero(fixed_advert);
+
+		set = phy_lookup_setting(phydev->speed, phydev->duplex,
+					 phydev->supported, true);
+		if (set)
+			linkmode_set_bit(set->bit, fixed_advert);
+
+		advert = fixed_advert;
+	}
 
-	err = genphy_config_advert(phydev);
+	err = genphy_config_advert(phydev, advert);
 	if (err < 0) /* error */
 		return err;
 	else if (err)