kernel: make mtd mac address increment more flexible

Allow selecting the byte on which the increment should be added.

Signed-off-by: Felix Fietkau <nbd@nbd.name>

target/linux/generic/pending-4.14/681-NET-add-of_get_mac_address_mtd.patch

@@ -32,7 +32,7 @@ Signed-off-by: Felix Fietkau <nbd@nbd.name>
  {
  	struct property *pp = of_find_property(np, name, NULL);
  
-@@ -47,6 +48,73 @@ static const void *of_get_mac_addr(struc
+@@ -47,6 +48,79 @@ static const void *of_get_mac_addr(struc
  	return NULL;
  }
  
@@ -50,6 +50,7 @@ Signed-off-by: Felix Fietkau <nbd@nbd.name>
 +	u32 mac_inc = 0;
 +	u8 mac[ETH_ALEN];
 +	void *addr;
++	u32 inc_idx;
 +
 +	list = of_get_property(np, "mtd-mac-address", &size);
 +	if (!list || (size != (2 * sizeof(*list))))
@@ -73,8 +74,13 @@ Signed-off-by: Felix Fietkau <nbd@nbd.name>
 +	ret = mtd_read(mtd, be32_to_cpup(list), 6, &retlen, mac);
 +	put_mtd_device(mtd);
 +
++	if (of_property_read_u32(np, "mtd-mac-address-increment-byte", &inc_idx))
++		inc_idx = 5;
++	if (inc_idx > 5)
++		return NULL;
++
 +	if (!of_property_read_u32(np, "mtd-mac-address-increment", &mac_inc))
-+		mac[5] += mac_inc;
++		mac[inc_idx] += mac_inc;
 +
 +	if (!is_valid_ether_addr(mac))
 +		return NULL;
@@ -106,7 +112,7 @@ Signed-off-by: Felix Fietkau <nbd@nbd.name>
  /**
   * Search the device tree for the best MAC address to use.  'mac-address' is
   * checked first, because that is supposed to contain to "most recent" MAC
-@@ -64,11 +132,18 @@ static const void *of_get_mac_addr(struc
+@@ -64,11 +138,18 @@ static const void *of_get_mac_addr(struc
   * addresses.  Some older U-Boots only initialized 'local-mac-address'.  In
   * this case, the real MAC is in 'local-mac-address', and 'mac-address' exists
   * but is all zeros.