net: introduce a helper to determine whether to use in-band autoneg

Certain serial SERDES protocols like 1000base-x, 2500base-x, SGMII,
USXGMII can operate either in a mode where the PHY (be it on-board or
inside an SFP module) passes the link parameters (speed, duplex, pause)
to the MAC through in-band through control words standardized by IEEE
802.3 clause 37, or in a mode where the MAC must configure (force) its
link parameters based on information obtained out-of-band (MDIO reads,
guesswork etc).

In Linux, the OF node property named "managed" is parsed by the phylink
framework, and the convention is that if a driver uses phylink, then the
presence of this property means that in-band autoneg should be enabled,
otherwise it shouldn't.

To be compatible with the OF node bindings of drivers that use phylink
in Linux, introduce parsing support for this property in U-Boot too.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Ramon Fried <rfried.dev@gmail.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Ramon Fried <rfried.dev@gmail.com>

drivers/core/of_extra.c

@@ -155,3 +155,15 @@ bool ofnode_phy_is_fixed_link(ofnode eth_node, ofnode *phy_node)
 
 	return true;
 }
+
+bool ofnode_eth_uses_inband_aneg(ofnode eth_node)
+{
+	bool inband_aneg = false;
+	const char *managed;
+
+	managed = ofnode_read_string(eth_node, "managed");
+	if (managed && !strcmp(managed, "in-band-status"))
+		inband_aneg = true;
+
+	return inband_aneg;
+}

include/dm/of_extra.h

@@ -114,4 +114,18 @@ int ofnode_decode_memory_region(ofnode config_node, const char *mem_type,
  */
 bool ofnode_phy_is_fixed_link(ofnode eth_node, ofnode *phy_node);
 
+/**
+ * ofnode_eth_uses_inband_aneg() - Detect whether MAC should use in-band autoneg
+ *
+ * This function detects whether the Ethernet controller should use IEEE 802.3
+ * clause 37 in-band autonegotiation for serial protocols such as 1000base-x,
+ * SGMII, USXGMII, etc. The property is relevant when the Ethernet controller
+ * is connected to an on-board PHY or an SFP cage, and is not relevant when it
+ * has a fixed link (in that case, in-band autoneg should not be used).
+ *
+ * @param eth_node	ofnode belonging to the Ethernet controller
+ * @return true if in-band autoneg should be used, false otherwise
+ */
+bool ofnode_eth_uses_inband_aneg(ofnode eth_node);
+
 #endif