[PATCH] arm/dt: Don't add disabled CPUs to system topology

[James King]

If CPUs are marked as disabled in the devicetree, make sure they do
not exist in the system CPU information and CPU topology information.
In this case these CPUs will not be able to be added to the system later
using hot-plug. This allows a single chip with many CPUs to be easily
used in a variety of hardware devices where they may have different
actual processing requirements (eg for thermal/cost reasons).

- Change devicetree.c to ignore any cpu nodes marked as disabled,
  this effectively limits the number of active cpu cores so no need
  for the max_cpus=x in the chosen node.
- Change topology.c to ignore any cpu nodes marked as disabled, this
  is where the scheduler would learn about big/LITTLE cores so this
  effectively keeps the scheduler in sync.

Signed-off-by: James King <james.king@xxxxxxxxxx>
---
 Documentation/devicetree/bindings/arm/cpus.txt | 5 +++++
 arch/arm/kernel/devtree.c                      | 6 ++++++
 arch/arm/kernel/topology.c                     | 4 ++++
 3 files changed, 15 insertions(+)

diff --git a/Documentation/devicetree/bindings/arm/cpus.txt b/Documentation/devicetree/bindings/arm/cpus.txt
index f32494d..9fbcbc5 100644
--- a/Documentation/devicetree/bindings/arm/cpus.txt
+++ b/Documentation/devicetree/bindings/arm/cpus.txt
@@ -45,6 +45,10 @@ For the ARM architecture every CPU node must contain the following properties:
 		"marvell,xsc3"
 		"marvell,xscale"
 
+And optionally set the following properties:
+
+- status:	can be set to "disabled" to remove that CPU from the system CPU topology
+
 Example:
 
 	cpus {
@@ -73,5 +77,6 @@ Example:
 			device_type = "cpu";
 			compatible = "arm,cortex-a7";
 			reg = <0x101>;
+			status = "disabled";
 		};
 	};
diff --git a/arch/arm/kernel/devtree.c b/arch/arm/kernel/devtree.c
index 5af04f6..f4ba8ee 100644
--- a/arch/arm/kernel/devtree.c
+++ b/arch/arm/kernel/devtree.c
@@ -112,6 +112,12 @@ void __init arm_dt_init_cpu_maps(void)
 			return;
 
 		/*
+		 * Check if the cpu is marked as "disabled", if so ignore.
+		 */
+		if (!of_device_is_available(cpu))
+			continue;
+
+		/*
 		 * Duplicate MPIDRs are a recipe for disaster.
 		 * Scan all initialized entries and check for
 		 * duplicates. If any is found just bail out.
diff --git a/arch/arm/kernel/topology.c b/arch/arm/kernel/topology.c
index f10316b..90f8fb3 100644
--- a/arch/arm/kernel/topology.c
+++ b/arch/arm/kernel/topology.c
@@ -116,6 +116,10 @@ static void __init parse_dt_topology(void)
 		if (cpu_eff->compatible == NULL)
 			continue;
 
+		/* Check if the cpu is marked as "disabled", if so ignore. */
+		if (!of_device_is_available(cn))
+			continue;
+
 		rate = of_get_property(cn, "clock-frequency", &len);
 		if (!rate || len != 4) {
 			pr_err("%s missing clock-frequency property\n",
-- 
1.8.1.2

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