net: ethernet: provide nvmem_get_mac_address()

We already have of_get_nvmem_mac_address() but some non-DT systems want
to read the MAC address from NVMEM too. Implement a generalized routine
that takes struct device as argument.
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/etherdevice.h

@@ -32,6 +32,7 @@
 struct device;
 int eth_platform_get_mac_address(struct device *dev, u8 *mac_addr);
 unsigned char *arch_get_platform_mac_address(void);
+int nvmem_get_mac_address(struct device *dev, void *addrbuf);
 u32 eth_get_headlen(void *data, unsigned int max_len);
 __be16 eth_type_trans(struct sk_buff *skb, struct net_device *dev);
 extern const struct header_ops eth_header_ops;

net/ethernet/eth.c

@@ -47,6 +47,7 @@
 #include <linux/inet.h>
 #include <linux/ip.h>
 #include <linux/netdevice.h>
+#include <linux/nvmem-consumer.h>
 #include <linux/etherdevice.h>
 #include <linux/skbuff.h>
 #include <linux/errno.h>
@@ -550,3 +551,40 @@ int eth_platform_get_mac_address(struct device *dev, u8 *mac_addr)
 	return 0;
 }
 EXPORT_SYMBOL(eth_platform_get_mac_address);
+
+/**
+ * Obtain the MAC address from an nvmem cell named 'mac-address' associated
+ * with given device.
+ *
+ * @dev:	Device with which the mac-address cell is associated.
+ * @addrbuf:	Buffer to which the MAC address will be copied on success.
+ *
+ * Returns 0 on success or a negative error number on failure.
+ */
+int nvmem_get_mac_address(struct device *dev, void *addrbuf)
+{
+	struct nvmem_cell *cell;
+	const void *mac;
+	size_t len;
+
+	cell = nvmem_cell_get(dev, "mac-address");
+	if (IS_ERR(cell))
+		return PTR_ERR(cell);
+
+	mac = nvmem_cell_read(cell, &len);
+	nvmem_cell_put(cell);
+
+	if (IS_ERR(mac))
+		return PTR_ERR(mac);
+
+	if (len != ETH_ALEN || !is_valid_ether_addr(mac)) {
+		kfree(mac);
+		return -EINVAL;
+	}
+
+	ether_addr_copy(addrbuf, mac);
+	kfree(mac);
+
+	return 0;
+}
+EXPORT_SYMBOL(nvmem_get_mac_address);