[RFC PATCH] Documentation: DT: arm: Add topology property to define package boundaries

[Lorenzo Pieralisi]

The current ARM DT topology description provides the operating system
with a topological view of the system that is based on leaf nodes
representing either cores or threads (in an SMT system) and a
hierarchical set of cluster nodes that creates a hierarchical topology
view of how those cores and threads are grouped.

As opposed to the ACPI topology description ([1], PPTT table), this
hierarchical representation of clusters does not allow to describe what
topology level actually represents the physical package boundary, which
is a key piece of information to be used by an operating system to
optimize resource allocation and scheduling.

Define an optional, backward compatible boolean property for cluster
nodes that, by reusing the ACPI nomenclature, add to the ARM DT
topological description a binding to define what cluster level
represents a physical package boundary.

[1] http://www.uefi.org/sites/default/files/resources/ACPI_6_2.pdf

Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi at arm.com>
Cc: Rob Herring <robh+dt at kernel.org>
Cc: Sudeep Holla <sudeep.holla at arm.com>
Cc: Jeremy Linton <jeremy.linton at arm.com>
Cc: Morten Rasmussen <morten.rasmussen at arm.com>
Cc: Mark Rutland <mark.rutland at arm.com>
---
 Documentation/devicetree/bindings/arm/topology.txt | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/Documentation/devicetree/bindings/arm/topology.txt b/Documentation/devicetree/bindings/arm/topology.txt
index de9eb0486630..8e78d76b0671 100644
--- a/Documentation/devicetree/bindings/arm/topology.txt
+++ b/Documentation/devicetree/bindings/arm/topology.txt
@@ -109,6 +109,15 @@ Bindings for cluster/cpu/thread nodes are defined as follows:
 	The cluster node name must be "clusterN" as described in 2.1 above.
 	A cluster node can not be a leaf node.
 
+	Properties for cluster nodes:
+
+	- physical-package
+		Usage: optional
+		Value type: <empty>
+		Definition: if present the cluster node represents the
+			    boundary of a physical package, whether socketed
+			    or surface mounted.
+
 	A cluster node's child nodes must be:
 
 	- one or more cluster nodes; or
-- 
2.15.0