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SubjectRe: [PATCH] arm/dt: Don't add disabled CPUs to system topology
On Thu, 6 Jun 2013, James King wrote:

> 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@linaro.org>

Acked-by: Nicolas Pitre <nico@linaro.org>


> ---
> 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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