Re: [PATCH 38/39] cpumask: Add enabled cpumask for present CPUs that can be brought online

Greg Kroah-Hartman
2023-10-24T16:02:38Z

On Tue, Oct 24, 2023 at 04:19:24PM +0100, Russell King wrote:
> From: James Morse <james.morse@arm.com>
>
> The 'offline' file in sysfs shows all offline CPUs, including those
> that aren't present. User-space is expected to remove not-present CPUs
> from this list to learn which CPUs could be brought online.
>
> CPUs can be present but not-enabled. These CPUs can't be brought online
> until the firmware policy changes, which comes with an ACPI notification
> that will register the CPUs.
>
> With only the offline and present files, user-space is unable to
> determine which CPUs it can try to bring online. Add a new CPU mask
> that shows this based on all the registered CPUs.
>
> Signed-off-by: James Morse <james.morse@arm.com>
> ---
> drivers/base/cpu.c | 10 ++++++++++
> include/linux/cpumask.h | 25 +++++++++++++++++++++++++
> kernel/cpu.c | 3 +++
> 3 files changed, 38 insertions(+)
>
> diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
> index 2b9cb2667654..f8bf1d4c7d71 100644
> --- a/drivers/base/cpu.c
> +++ b/drivers/base/cpu.c
> @@ -95,6 +95,7 @@ void unregister_cpu(struct cpu *cpu)
> {
> int logical_cpu = cpu->dev.id;
>
> + set_cpu_enabled(logical_cpu, false);
> unregister_cpu_under_node(logical_cpu, cpu_to_node(logical_cpu));
>
> device_unregister(&cpu->dev);
> @@ -273,6 +274,13 @@ static ssize_t print_cpus_offline(struct device *dev,
> }
> static DEVICE_ATTR(offline, 0444, print_cpus_offline, NULL);
>
> +static ssize_t print_cpus_enabled(struct device *dev,
> + struct device_attribute *attr, char *buf)
> +{
> + return sysfs_emit(buf, "%*pbl\n", cpumask_pr_args(cpu_enabled_mask));
> +}
> +static DEVICE_ATTR(enabled, 0444, print_cpus_enabled, NULL);

This needs to be documented somewhere in Documentation/ABI/ did I miss
that patch?

thanks,

greg k-h