dt/net: add helper function of_get_phy_mode

It adds the helper function of_get_phy_mode getting phy interface
from device tree.
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Cc: Grant Likely <grant.likely@secretlab.ca>
Acked-by: Grant Likely <grant.likely@secretlab.ca>
Acked-by: David Miller <davem@davemloft.net>

drivers/of/of_net.c

@@ -8,6 +8,49 @@
 #include <linux/etherdevice.h>
 #include <linux/kernel.h>
 #include <linux/of_net.h>
+#include <linux/phy.h>
+
+/**
+ * It maps 'enum phy_interface_t' found in include/linux/phy.h
+ * into the device tree binding of 'phy-mode', so that Ethernet
+ * device driver can get phy interface from device tree.
+ */
+static const char *phy_modes[] = {
+	[PHY_INTERFACE_MODE_MII]	= "mii",
+	[PHY_INTERFACE_MODE_GMII]	= "gmii",
+	[PHY_INTERFACE_MODE_SGMII]	= "sgmii",
+	[PHY_INTERFACE_MODE_TBI]	= "tbi",
+	[PHY_INTERFACE_MODE_RMII]	= "rmii",
+	[PHY_INTERFACE_MODE_RGMII]	= "rgmii",
+	[PHY_INTERFACE_MODE_RGMII_ID]	= "rgmii-id",
+	[PHY_INTERFACE_MODE_RGMII_RXID]	= "rgmii-rxid",
+	[PHY_INTERFACE_MODE_RGMII_TXID] = "rgmii-txid",
+	[PHY_INTERFACE_MODE_RTBI]	= "rtbi",
+};
+
+/**
+ * of_get_phy_mode - Get phy mode for given device_node
+ * @np:	Pointer to the given device_node
+ *
+ * The function gets phy interface string from property 'phy-mode',
+ * and return its index in phy_modes table, or errno in error case.
+ */
+const int of_get_phy_mode(struct device_node *np)
+{
+	const char *pm;
+	int err, i;
+
+	err = of_property_read_string(np, "phy-mode", &pm);
+	if (err < 0)
+		return err;
+
+	for (i = 0; i < ARRAY_SIZE(phy_modes); i++)
+		if (!strcasecmp(pm, phy_modes[i]))
+			return i;
+
+	return -ENODEV;
+}
+EXPORT_SYMBOL_GPL(of_get_phy_mode);
 
 /**
  * Search the device tree for the best MAC address to use.  'mac-address' is

include/linux/of_net.h

@@ -9,6 +9,7 @@
 
 #ifdef CONFIG_OF_NET
 #include <linux/of.h>
+extern const int of_get_phy_mode(struct device_node *np);
 extern const void *of_get_mac_address(struct device_node *np);
 #endif