net: phylink: make Broadcom BCM84881 based SFPs work

The Broadcom BCM84881 does not appear to send the SGMII control word
when operating in SGMII mode, which causes network adapters to fail
to link with the PHY, or decide to operate at fixed 1G speed, even if
the PHY negotiated 100M.

Work around this by detecting the Broadcom BCM84881 and switch to phy
mode rather than inband mode.

Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>

Author: Russell King

drivers/net/phy/phylink.c

@@ -1837,10 +1837,20 @@ static void phylink_sfp_link_up(void *upstream)
 	phylink_run_resolve(pl);
 }
 
+/* The Broadcom BCM84881 in the Methode DM7052 is unable to provide a SGMII
+ * or 802.3z control word, so inband will not work.
+ */
+static bool phylink_phy_no_inband(struct phy_device *phy)
+{
+	return phy->is_c45 &&
+		(phy->c45_ids.device_ids[1] & 0xfffffff0) == 0xae025150;
+}
+
 static int phylink_sfp_connect_phy(void *upstream, struct phy_device *phy)
 {
 	struct phylink *pl = upstream;
 	phy_interface_t interface;
+	u8 mode;
 	int ret;
 
 	/*
@@ -1852,9 +1862,13 @@ static int phylink_sfp_connect_phy(void *upstream, struct phy_device *phy)
 	 */
 	phy_support_asym_pause(phy);
 
+	if (phylink_phy_no_inband(phy))
+		mode = MLO_AN_PHY;
+	else
+		mode = MLO_AN_INBAND;
+
 	/* Do the initial configuration */
-	ret = phylink_sfp_config(pl, MLO_AN_INBAND, phy->supported,
-				 phy->advertising);
+	ret = phylink_sfp_config(pl, mode, phy->supported, phy->advertising);
 	if (ret < 0)
 		return ret;