net: stmmac: implement support for passive mode converters via dt

In-between the MAC & PHY there can be a mode converter, which converts one
mode to another (e.g. GMII-to-RGMII).

The converter, can be passive (i.e. no driver or OS/SW information
required), so the MAC & PHY need to be configured differently.

For the `stmmac` driver, this is implemented via a `mac-mode` property in
the device-tree, which configures the MAC into a certain mode, and for the
PHY a `phy_interface` field will hold the mode of the PHY. The mode of the
PHY will be passed to the PHY and from there-on it work in a different
mode. If unspecified, the default `phy-mode` will be used for both.

Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/stmicro/stmmac/stmmac_main.c

@@ -1036,7 +1036,7 @@ static int stmmac_init_phy(struct net_device *dev)
 static int stmmac_phy_setup(struct stmmac_priv *priv)
 {
 	struct fwnode_handle *fwnode = of_fwnode_handle(priv->plat->phylink_node);
-	int mode = priv->plat->interface;
+	int mode = priv->plat->phy_interface;
 	struct phylink *phylink;
 
 	priv->phylink_config.dev = &priv->dev->dev;

drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c

@@ -358,6 +358,32 @@ static int stmmac_dt_phy(struct plat_stmmacenet_data *plat,
 	return 0;
 }
 
+/**
+ * stmmac_of_get_mac_mode - retrieves the interface of the MAC
+ * @np - device-tree node
+ * Description:
+ * Similar to `of_get_phy_mode()`, this function will retrieve (from
+ * the device-tree) the interface mode on the MAC side. This assumes
+ * that there is mode converter in-between the MAC & PHY
+ * (e.g. GMII-to-RGMII).
+ */
+static int stmmac_of_get_mac_mode(struct device_node *np)
+{
+	const char *pm;
+	int err, i;
+
+	err = of_property_read_string(np, "mac-mode", &pm);
+	if (err < 0)
+		return err;
+
+	for (i = 0; i < PHY_INTERFACE_MODE_MAX; i++) {
+		if (!strcasecmp(pm, phy_modes(i)))
+			return i;
+	}
+
+	return -ENODEV;
+}
+
 /**
  * stmmac_probe_config_dt - parse device-tree driver parameters
  * @pdev: platform_device structure
@@ -386,7 +412,13 @@ stmmac_probe_config_dt(struct platform_device *pdev, const char **mac)
 		*mac = NULL;
 	}
 
-	plat->interface = of_get_phy_mode(np);
+	plat->phy_interface = of_get_phy_mode(np);
+	if (plat->phy_interface < 0)
+		return ERR_PTR(plat->phy_interface);
+
+	plat->interface = stmmac_of_get_mac_mode(np);
+	if (plat->interface < 0)
+		plat->interface = plat->phy_interface;
 
 	/* Some wrapper drivers still rely on phy_node. Let's save it while
 	 * they are not converted to phylink. */

include/linux/stmmac.h

@@ -131,6 +131,7 @@ struct plat_stmmacenet_data {
 	int bus_id;
 	int phy_addr;
 	int interface;
+	int phy_interface;
 	struct stmmac_mdio_bus_data *mdio_bus_data;
 	struct device_node *phy_node;
 	struct device_node *phylink_node;