linux-kernel - Re: [PATCH v5 01/10] x86/acpi: Add a helper functions to setup and access the wakeup mailbox

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Message-ID: <CAJZ5v0i+EOthnNexMs7hm1iX+PY0rCNCHjRgB5r5pJ3tz2aw+w@mail.gmail.com>
Date: Mon, 30 Jun 2025 20:55:25 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
Cc: x86@...nel.org, Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Rob Herring <robh@...nel.org>, "K. Y. Srinivasan" <kys@...rosoft.com>, 
	Haiyang Zhang <haiyangz@...rosoft.com>, Wei Liu <wei.liu@...nel.org>, 
	Dexuan Cui <decui@...rosoft.com>, Michael Kelley <mhklinux@...look.com>, 
	"Rafael J. Wysocki" <rafael@...nel.org>, Saurabh Sengar <ssengar@...ux.microsoft.com>, 
	Chris Oo <cho@...rosoft.com>, "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>, 
	linux-hyperv@...r.kernel.org, devicetree@...r.kernel.org, 
	linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Ricardo Neri <ricardo.neri@...el.com>
Subject: Re: [PATCH v5 01/10] x86/acpi: Add a helper functions to setup and
 access the wakeup mailbox

s/a helper/helper/ in the subject.

On Sat, Jun 28, 2025 at 5:35 AM Ricardo Neri
<ricardo.neri-calderon@...ux.intel.com> wrote:
>
> In preparation to move the functionality to wake secondary CPUs up out of
> the ACPI code, add two helper functions.
>
> The function acpi_setup_mp_wakeup_mailbox() stores the physical address of
> the mailbox and updates the wakeup_secondary_cpu_64() APIC callback.
>
> There is a slight change in behavior: now the APIC callback is updated
> before configuring CPU hotplug offline behavior. This is fine as the APIC
> callback continues to be updated unconditionally, regardless of the
> restriction on CPU offlining.
>
> The function acpi_madt_multiproc_wakeup_mailbox() returns a pointer to the
> mailbox. Use this helper function only in the portions of the code for
> which the variable acpi_mp_wake_mailbox will be out of scope once it is
> relocated out of the ACPI directory.
>
> The wakeup mailbox is only supported for CONFIG_X86_64 and needed only with
> CONFIG_SMP=y.
>
> Signed-off-by: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>

With the above nit addressed

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

> ---
> Changes since v4:
>  - None
>
> Changes since v3:
>  - Squashed the two first patches of the series into one, both introduce
>    helper functions. (Rafael)
>  - Renamed setup_mp_wakeup_mailbox() as acpi_setup_mp_wakeup_mailbox().
>    (Rafael)
>  - Dropped the function prototype for !CONFIG_X86_64. (Rafael)
>
> Changes since v2:
>  - Introduced this patch.
>
> Changes since v1:
>  - N/A
> ---
>  arch/x86/include/asm/smp.h         |  3 +++
>  arch/x86/kernel/acpi/madt_wakeup.c | 20 +++++++++++++++-----
>  2 files changed, 18 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/include/asm/smp.h b/arch/x86/include/asm/smp.h
> index 0c1c68039d6f..77dce560a70a 100644
> --- a/arch/x86/include/asm/smp.h
> +++ b/arch/x86/include/asm/smp.h
> @@ -146,6 +146,9 @@ static inline struct cpumask *cpu_l2c_shared_mask(int cpu)
>         return per_cpu(cpu_l2c_shared_map, cpu);
>  }
>
> +void acpi_setup_mp_wakeup_mailbox(u64 addr);
> +struct acpi_madt_multiproc_wakeup_mailbox *acpi_get_mp_wakeup_mailbox(void);
> +
>  #else /* !CONFIG_SMP */
>  #define wbinvd_on_cpu(cpu)     wbinvd()
>  static inline int wbinvd_on_all_cpus(void)
> diff --git a/arch/x86/kernel/acpi/madt_wakeup.c b/arch/x86/kernel/acpi/madt_wakeup.c
> index 6d7603511f52..c3ac5ecf3e7d 100644
> --- a/arch/x86/kernel/acpi/madt_wakeup.c
> +++ b/arch/x86/kernel/acpi/madt_wakeup.c
> @@ -37,6 +37,7 @@ static void acpi_mp_play_dead(void)
>
>  static void acpi_mp_cpu_die(unsigned int cpu)
>  {
> +       struct acpi_madt_multiproc_wakeup_mailbox *mailbox = acpi_get_mp_wakeup_mailbox();
>         u32 apicid = per_cpu(x86_cpu_to_apicid, cpu);
>         unsigned long timeout;
>
> @@ -46,13 +47,13 @@ static void acpi_mp_cpu_die(unsigned int cpu)
>          *
>          * BIOS has to clear 'command' field of the mailbox.
>          */
> -       acpi_mp_wake_mailbox->apic_id = apicid;
> -       smp_store_release(&acpi_mp_wake_mailbox->command,
> +       mailbox->apic_id = apicid;
> +       smp_store_release(&mailbox->command,
>                           ACPI_MP_WAKE_COMMAND_TEST);
>
>         /* Don't wait longer than a second. */
>         timeout = USEC_PER_SEC;
> -       while (READ_ONCE(acpi_mp_wake_mailbox->command) && --timeout)
> +       while (READ_ONCE(mailbox->command) && --timeout)
>                 udelay(1);
>
>         if (!timeout)
> @@ -227,7 +228,7 @@ int __init acpi_parse_mp_wake(union acpi_subtable_headers *header,
>
>         acpi_table_print_madt_entry(&header->common);
>
> -       acpi_mp_wake_mailbox_paddr = mp_wake->mailbox_address;
> +       acpi_setup_mp_wakeup_mailbox(mp_wake->mailbox_address);
>
>         if (mp_wake->version >= ACPI_MADT_MP_WAKEUP_VERSION_V1 &&
>             mp_wake->header.length >= ACPI_MADT_MP_WAKEUP_SIZE_V1) {
> @@ -243,7 +244,16 @@ int __init acpi_parse_mp_wake(union acpi_subtable_headers *header,
>                 acpi_mp_disable_offlining(mp_wake);
>         }
>
> +       return 0;
> +}
> +
> +void __init acpi_setup_mp_wakeup_mailbox(u64 mailbox_paddr)
> +{
> +       acpi_mp_wake_mailbox_paddr = mailbox_paddr;
>         apic_update_callback(wakeup_secondary_cpu_64, acpi_wakeup_cpu);
> +}
>
> -       return 0;
> +struct acpi_madt_multiproc_wakeup_mailbox *acpi_get_mp_wakeup_mailbox(void)
> +{
> +       return acpi_mp_wake_mailbox;
>  }
>
> --
> 2.43.0
>