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From:   "Rafael J. Wysocki" <rafael@kernel.org>
Date:   Wed, 22 Nov 2023 21:16:39 +0100
Message-ID: <CAJZ5v0iYRXh369M3XTM0V8Q9mWkAT2y+9pJMD7HMaGjgpvFEMw@mail.gmail.com>
Subject: Re: [PATCH 05/21] ACPI: Move ACPI_HOTPLUG_CPU to be disabled on arm64
 and riscv
To:     Russell King <rmk+kernel@armlinux.org.uk>
Cc:     linux-pm@vger.kernel.org, loongarch@lists.linux.dev,
        linux-acpi@vger.kernel.org, linux-arch@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-riscv@lists.infradead.org, kvmarm@lists.linux.dev,
        x86@kernel.org, linux-csky@vger.kernel.org,
        linux-doc@vger.kernel.org, linux-ia64@vger.kernel.org,
        linux-parisc@vger.kernel.org, Salil Mehta <salil.mehta@huawei.com>,
        Jean-Philippe Brucker <jean-philippe@linaro.org>,
        jianyong.wu@arm.com, justin.he@arm.com,
        James Morse <james.morse@arm.com>,
        Huacai Chen <chenhuacai@kernel.org>,
        WANG Xuerui <kernel@xen0n.name>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        "H. Peter Anvin" <hpa@zytor.com>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Len Brown <lenb@kernel.org>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>
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On Tue, Nov 21, 2023 at 2:44 PM Russell King <rmk+kernel@armlinux.org.uk> wrote:
>
> From: James Morse <james.morse@arm.com>
>
> Neither arm64 nor riscv support physical hotadd of CPUs that were not
> present at boot. For arm64 much of the platform description is in static
> tables which do not have update methods. arm64 does support HOTPLUG_CPU,
> which is backed by a firmware interface to turn CPUs on and off.
>
> acpi_processor_hotadd_init() and acpi_processor_remove() are for adding
> and removing CPUs that were not present at boot. arm64 systems that do this
> are not supported as there is currently insufficient information in the
> platform description. (e.g. did the GICR get removed too?)
>
> arm64 currently relies on the MADT enabled flag check in map_gicc_mpidr()
> to prevent CPUs that were not described as present at boot from being
> added to the system. Similarly, riscv relies on the same check in
> map_rintc_hartid(). Both architectures also rely on the weak 'always fails'
> definitions of acpi_map_cpu() and arch_register_cpu().
>
> Subsequent changes will redefine ACPI_HOTPLUG_CPU as making possible
> CPUs present. Neither arm64 nor riscv support this.
>
> Disable ACPI_HOTPLUG_CPU for arm64 and riscv by removing 'default y' and
> selecting it on the other three ACPI architectures. This allows the weak
> definitions of some symbols to be removed.
>
> Signed-off-by: James Morse <james.morse@arm.com>
> Reviewed-by: Shaoqin Huang <shahuang@redhat.com>
> Reviewed-by: Gavin Shan <gshan@redhat.com>
> Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>

I can apply this if it gets ACKs from the maintainers of the affected
architectures.

> ---
> Changes since RFC:
>  * Expanded conditions to avoid ACPI_HOTPLUG_CPU being enabled when
>    HOTPLUG_CPU isn't.
> Changes since RFC v3:
>  * Dropped ia64 changes
> ---
>  arch/loongarch/Kconfig        |  1 +
>  arch/x86/Kconfig              |  1 +
>  drivers/acpi/Kconfig          |  1 -
>  drivers/acpi/acpi_processor.c | 18 ------------------
>  4 files changed, 2 insertions(+), 19 deletions(-)
>
> diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
> index ee123820a476..331becb2cb4f 100644
> --- a/arch/loongarch/Kconfig
> +++ b/arch/loongarch/Kconfig
> @@ -5,6 +5,7 @@ config LOONGARCH
>         select ACPI
>         select ACPI_GENERIC_GSI if ACPI
>         select ACPI_MCFG if ACPI
> +       select ACPI_HOTPLUG_CPU if ACPI_PROCESSOR && HOTPLUG_CPU
>         select ACPI_PPTT if ACPI
>         select ACPI_SYSTEM_POWER_STATES_SUPPORT if ACPI
>         select ARCH_BINFMT_ELF_STATE
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 3762f41bb092..dbdcfc708369 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -59,6 +59,7 @@ config X86
>         #
>         select ACPI_LEGACY_TABLES_LOOKUP        if ACPI
>         select ACPI_SYSTEM_POWER_STATES_SUPPORT if ACPI
> +       select ACPI_HOTPLUG_CPU                 if ACPI_PROCESSOR && HOTPLUG_CPU
>         select ARCH_32BIT_OFF_T                 if X86_32
>         select ARCH_CLOCKSOURCE_INIT
>         select ARCH_CORRECT_STACKTRACE_ON_KRETPROBE
> diff --git a/drivers/acpi/Kconfig b/drivers/acpi/Kconfig
> index f819e760ff19..a3acfc750fce 100644
> --- a/drivers/acpi/Kconfig
> +++ b/drivers/acpi/Kconfig
> @@ -310,7 +310,6 @@ config ACPI_HOTPLUG_CPU
>         bool
>         depends on ACPI_PROCESSOR && HOTPLUG_CPU
>         select ACPI_CONTAINER
> -       default y
>
>  config ACPI_PROCESSOR_AGGREGATOR
>         tristate "Processor Aggregator"
> diff --git a/drivers/acpi/acpi_processor.c b/drivers/acpi/acpi_processor.c
> index 0f5218e361df..4fe2ef54088c 100644
> --- a/drivers/acpi/acpi_processor.c
> +++ b/drivers/acpi/acpi_processor.c
> @@ -184,24 +184,6 @@ static void __init acpi_pcc_cpufreq_init(void) {}
>
>  /* Initialization */
>  #ifdef CONFIG_ACPI_HOTPLUG_CPU
> -int __weak acpi_map_cpu(acpi_handle handle,
> -               phys_cpuid_t physid, u32 acpi_id, int *pcpu)
> -{
> -       return -ENODEV;
> -}
> -
> -int __weak acpi_unmap_cpu(int cpu)
> -{
> -       return -ENODEV;
> -}
> -
> -int __weak arch_register_cpu(int cpu)
> -{
> -       return -ENODEV;
> -}
> -
> -void __weak arch_unregister_cpu(int cpu) {}
> -
>  static int acpi_processor_hotadd_init(struct acpi_processor *pr)
>  {
>         unsigned long long sta;
> --
> 2.30.2
>