[PATCH v4] Documentation, dt, numa: Add note to empty NUMA node

[Gavin Shan <gshan@redhat.com>]

The empty memory nodes, where no memory resides in, are allowed.
For these empty memory nodes, the 'len' of 'reg' property is zero.
The NUMA node IDs are still valid and parsed, but memory can be
added to them through hotplug afterwards. I finds difficulty to
get where it's properly documented.

So lets add note to empty memory nodes in the NUMA binding doc.

Signed-off-by: Gavin Shan <gshan@redhat.com>
---
 Documentation/devicetree/bindings/numa.txt | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/Documentation/devicetree/bindings/numa.txt b/Documentation/devicetree/bindings/numa.txt
index 21b35053ca5a..0fc882e44270 100644
--- a/Documentation/devicetree/bindings/numa.txt
+++ b/Documentation/devicetree/bindings/numa.txt
@@ -109,6 +109,10 @@ Example:
 Dual socket system consists of 2 boards connected through ccn bus and
 each board having one socket/soc of 8 cpus, memory and pci bus.
 
+Note that empty memory nodes, which no memory resides in, are allowed.
+The NUMA node IDs in these empty memory nodes are still valid, but
+memory can be added into them through hotplug afterwards.
+
 	memory@c00000 {
 		device_type = "memory";
 		reg = <0x0 0xc00000 0x0 0x80000000>;
-- 
2.23.0