Documentation: LEDs: Describe good names for network LEDs

Network LEDs can exist in both the MAC and the PHY. Naming is
difficult because the netdev name is neither stable or unique, do to
commands like ip link set name eth42 dev eth0, and network
namesspaces.

Give some example names where the MAC and the PHY have unique names
based on device tree nodes, or PCI bus addresses.

Since the LED can be used for anything which Linux supports for LEDs,
avoid using names like activity or link, rather describe the location
on the RJ-45, of what the RJ-45 is expected to be used for, WAN/LAN
etc.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/leds/well-known-leds.txt

@@ -70,3 +70,33 @@ Good: "platform:*:charging" (allwinner sun50i)
 * Screen
 
 Good: ":backlight" (Motorola Droid 4)
+
+* Ethernet LEDs
+
+Currently two types of Network LEDs are support, those controlled by
+the PHY and those by the MAC. In theory both can be present at the
+same time for one Linux netdev, hence the names need to differ between
+MAC and PHY.
+
+Do not use the netdev name, such as eth0, enp1s0. These are not stable
+and are not unique. They also don't differentiate between MAC and PHY.
+
+** MAC LEDs
+
+Good: f1070000.ethernet:white:WAN
+Good: mdio_mux-0.1:00:green:left
+Good: 0000:02:00.0:yellow:top
+
+The first part must uniquely name the MAC controller. Then follows the
+colour.  WAN/LAN should be used for a single LED. If there are
+multiple LEDs, use left/right, or top/bottom to indicate their
+position on the RJ45 socket.
+
+** PHY LEDs
+
+Good: f1072004.mdio-mii:00: white:WAN
+Good: !mdio-mux!mdio@2!switch@0!mdio:01:green:right
+Good: r8169-0-200:00:yellow:bottom
+
+The first part must uniquely name the PHY. This often means uniquely
+identifying the MDIO bus controller, and the address on the bus.