Re: [PATCH v3 01/13] x86/acpi: Add a helper function to setup the wakeup mailbox

Rafael J. Wysocki
2025-05-05T09:50:23Z

On Sat, May 3, 2025 at 9:10 PM Ricardo Neri
<ricardo.neri-calderon@linux.intel.com> wrote:
>
> In preparation to move the functionality to wake secondary CPUs up out of
> the ACPI code, add a helper function that 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 wakeup mailbox is only supported for CONFIG_X86_64 and needed only with
> CONFIG_SMP=y.
>
> Signed-off-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
> ---
> Changes since v2:
> - Introduced this patch.
>
> Changes since v1:
> - N/A
> ---
> arch/x86/include/asm/smp.h | 4 ++++
> arch/x86/kernel/acpi/madt_wakeup.c | 10 +++++++---
> 2 files changed, 11 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/include/asm/smp.h b/arch/x86/include/asm/smp.h
> index 0c1c68039d6f..3622951d2ee0 100644
> --- a/arch/x86/include/asm/smp.h
> +++ b/arch/x86/include/asm/smp.h
> @@ -146,6 +146,10 @@ static inline struct cpumask *cpu_l2c_shared_mask(int cpu)
> return per_cpu(cpu_l2c_shared_map, cpu);
> }
>
> +#ifdef CONFIG_X86_64
> +void setup_mp_wakeup_mailbox(u64 addr);
> +#endif

The #ifdef is only necessary if you are going to provide an
alternative for builds in which the symbol is unset.

> +
> #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 f36f28405dcc..04de3db307de 100644
> --- a/arch/x86/kernel/acpi/madt_wakeup.c
> +++ b/arch/x86/kernel/acpi/madt_wakeup.c
> @@ -227,7 +227,7 @@ 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;
> + setup_mp_wakeup_mailbox(mp_wake->mailbox_address);

I'd prefer acpi_setup_mp_wakeup_mailbox().

>
> if (mp_wake->version >= ACPI_MADT_MP_WAKEUP_VERSION_V1 &&
> mp_wake->header.length >= ACPI_MADT_MP_WAKEUP_SIZE_V1) {
> @@ -243,7 +243,11 @@ int __init acpi_parse_mp_wake(union acpi_subtable_headers *header,
> acpi_mp_disable_offlining(mp_wake);
> }
>
> - apic_update_callback(wakeup_secondary_cpu_64, acpi_wakeup_cpu);
> -
> return 0;
> }
> +
> +void __init setup_mp_wakeup_mailbox(u64 mailbox_paddr)
> +{
> + acpi_mp_wake_mailbox_paddr = mailbox_paddr;
> + apic_update_callback(wakeup_secondary_cpu_64, acpi_wakeup_cpu);
> +}
> --
> 2.43.0
>
>