linux-kernel - Re: [RFC PATCH v2 27/35] ACPICA: Add new MADT GICC flags fields [code first?]

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Message-ID: <CAMj1kXHRAt7ecB9p_dm3MjDL5wZkAsVh30hMY2SV_XUe=bm6Vg@mail.gmail.com>
Date:   Thu, 14 Sep 2023 09:57:44 +0200
From:   Ard Biesheuvel <ardb@...nel.org>
To:     James Morse <james.morse@....com>
Cc:     linux-pm@...r.kernel.org, loongarch@...ts.linux.dev,
        linux-acpi@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-riscv@...ts.infradead.org, kvmarm@...ts.linux.dev,
        x86@...nel.org, Salil Mehta <salil.mehta@...wei.com>,
        Russell King <linux@...linux.org.uk>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        jianyong.wu@....com, justin.he@....com
Subject: Re: [RFC PATCH v2 27/35] ACPICA: Add new MADT GICC flags fields [code first?]

Hello James,

On Wed, 13 Sept 2023 at 18:41, James Morse <james.morse@....com> wrote:
>
> Add the new flag field to the MADT's GICC structure.
>
> 'Online Capable' indicates a disabled CPU can be enabled later.
>

Why do we need a bit for this? What would be the point of describing
disabled CPUs that cannot be enabled (and are you are aware of
firmware doing this?).

So why are we not able to assume that this new bit can always be treated as '1'?


> Signed-off-by: James Morse <james.morse@....com>
> ---
> This patch probably needs to go via the upstream acpica project,
> but is included here so the feature can be testd.
> ---
>  include/acpi/actbl2.h | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/include/acpi/actbl2.h b/include/acpi/actbl2.h
> index 3751ae69432f..c433a079d8e1 100644
> --- a/include/acpi/actbl2.h
> +++ b/include/acpi/actbl2.h
> @@ -1046,6 +1046,7 @@ struct acpi_madt_generic_interrupt {
>  /* ACPI_MADT_ENABLED                    (1)      Processor is usable if set */
>  #define ACPI_MADT_PERFORMANCE_IRQ_MODE  (1<<1) /* 01: Performance Interrupt Mode */
>  #define ACPI_MADT_VGIC_IRQ_MODE         (1<<2) /* 02: VGIC Maintenance Interrupt mode */
> +#define ACPI_MADT_GICC_CPU_CAPABLE      (1<<3) /* 03: CPU is online capable */
>
>  /* 12: Generic Distributor (ACPI 5.0 + ACPI 6.0 changes) */
>
> --
> 2.39.2
>