linux-kernel - Re: [PATCH v5 2/4] ACPI/PPTT: Add function to return ACPI 6.3 Identical tokens

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Date:   Thu, 27 Jun 2019 13:15:26 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Jeremy Linton <jeremy.linton@....com>
Cc:     Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Sudeep Holla <sudeep.holla@....com>,
        Hanjun Gou <gouhanjun@...wei.com>
Subject: Re: [PATCH v5 2/4] ACPI/PPTT: Add function to return ACPI 6.3
 Identical tokens

On Wed, Jun 26, 2019 at 11:37 PM Jeremy Linton <jeremy.linton@....com> wrote:
>
> ACPI 6.3 adds a flag to indicate that child nodes are all
> identical cores. This is useful to authoritatively determine
> if a set of (possibly offline) cores are identical or not.
>
> Since the flag doesn't give us a unique id we can generate
> one and use it to create bitmaps of sibling nodes, or simply
> in a loop to determine if a subset of cores are identical.
>
> Tested-by: Hanjun Gou <gouhanjun@...wei.com>
> Reviewed-by: Sudeep Holla <sudeep.holla@....com>
> Signed-off-by: Jeremy Linton <jeremy.linton@....com>

Assuming that the Tested-by tag will be fixed:

Acked-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

> ---
>  drivers/acpi/pptt.c  | 26 ++++++++++++++++++++++++++
>  include/linux/acpi.h |  5 +++++
>  2 files changed, 31 insertions(+)
>
> diff --git a/drivers/acpi/pptt.c b/drivers/acpi/pptt.c
> index 05344413f199..1e7ac0bd0d3a 100644
> --- a/drivers/acpi/pptt.c
> +++ b/drivers/acpi/pptt.c
> @@ -683,3 +683,29 @@ int find_acpi_cpu_topology_package(unsigned int cpu)
>         return find_acpi_cpu_topology_tag(cpu, PPTT_ABORT_PACKAGE,
>                                           ACPI_PPTT_PHYSICAL_PACKAGE);
>  }
> +
> +/**
> + * find_acpi_cpu_topology_hetero_id() - Get a core architecture tag
> + * @cpu: Kernel logical CPU number
> + *
> + * Determine a unique heterogeneous tag for the given CPU. CPUs with the same
> + * implementation should have matching tags.
> + *
> + * The returned tag can be used to group peers with identical implementation.
> + *
> + * The search terminates when a level is found with the identical implementation
> + * flag set or we reach a root node.
> + *
> + * Due to limitations in the PPTT data structure, there may be rare situations
> + * where two cores in a heterogeneous machine may be identical, but won't have
> + * the same tag.
> + *
> + * Return: -ENOENT if the PPTT doesn't exist, or the CPU cannot be found.
> + * Otherwise returns a value which represents a group of identical cores
> + * similar to this CPU.
> + */
> +int find_acpi_cpu_topology_hetero_id(unsigned int cpu)
> +{
> +       return find_acpi_cpu_topology_tag(cpu, PPTT_ABORT_PACKAGE,
> +                                         ACPI_PPTT_ACPI_IDENTICAL);
> +}
> diff --git a/include/linux/acpi.h b/include/linux/acpi.h
> index d315d86844e4..5bcd23e5ccd6 100644
> --- a/include/linux/acpi.h
> +++ b/include/linux/acpi.h
> @@ -1303,6 +1303,7 @@ static inline int lpit_read_residency_count_address(u64 *address)
>  #ifdef CONFIG_ACPI_PPTT
>  int find_acpi_cpu_topology(unsigned int cpu, int level);
>  int find_acpi_cpu_topology_package(unsigned int cpu);
> +int find_acpi_cpu_topology_hetero_id(unsigned int cpu);
>  int find_acpi_cpu_cache_topology(unsigned int cpu, int level);
>  #else
>  static inline int find_acpi_cpu_topology(unsigned int cpu, int level)
> @@ -1313,6 +1314,10 @@ static inline int find_acpi_cpu_topology_package(unsigned int cpu)
>  {
>         return -EINVAL;
>  }
> +static inline int find_acpi_cpu_topology_hetero_id(unsigned int cpu)
> +{
> +       return -EINVAL;
> +}
>  static inline int find_acpi_cpu_cache_topology(unsigned int cpu, int level)
>  {
>         return -EINVAL;
> --
> 2.21.0
>