linux-kernel - Re: [PATCH v4 31/35] armv8: cpu: Enable ACPI parking protocol

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Message-ID: <CAFLszTgYwRc+1c3p+bg13T3Jz4r3=ZCuwioc3vcNS3CR9FUqyA@mail.gmail.com>
Date: Thu, 19 Sep 2024 16:09:54 +0200
From: Simon Glass <sjg@...omium.org>
To: Patrick Rudolph <patrick.rudolph@...ements.com>
Cc: u-boot@...ts.denx.de, linux-kernel@...r.kernel.org, 
	Tom Rini <trini@...sulko.com>
Subject: Re: [PATCH v4 31/35] armv8: cpu: Enable ACPI parking protocol

On Wed, 18 Sept 2024 at 17:27, Patrick Rudolph
<patrick.rudolph@...ements.com> wrote:
>
> Update the generic entry point code to support the ACPI parking protocol.
> The ACPI parking protocol can be used when PSCI is not available to bring
> up secondary CPU cores.
>
> When enabled secondary CPUs will enter U-Boot proper and spin in their own
> 4KiB reserved memory page, which also acts as mailbox with the OS to
> release the CPU.
>
> TEST: Boots all CPUs on qemu-system-aarch64 -machine raspi4b
>
> Signed-off-by: Patrick Rudolph <patrick.rudolph@...ements.com>
> ---
>  arch/arm/cpu/armv8/start.S | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
>

Reviewed-by: Simon Glass <sjg@...omium.org>


> diff --git a/arch/arm/cpu/armv8/start.S b/arch/arm/cpu/armv8/start.S
> index 7461280261..544a4a5364 100644
> --- a/arch/arm/cpu/armv8/start.S
> +++ b/arch/arm/cpu/armv8/start.S
> @@ -178,6 +178,18 @@ pie_fixup_done:
>         branch_if_master x0, master_cpu
>         b       spin_table_secondary_jump
>         /* never return */
> +#elif defined(CONFIG_ACPI_PARKING_PROTOCOL) && !defined(CONFIG_SPL_BUILD)
> +       branch_if_master x0, master_cpu
> +       /*
> +        * Waits for ACPI parking protocol memory to be allocated and the spin-table
> +        * code to be written. Once ready the secondary CPUs will jump and spin in
> +        * their own 4KiB memory region, which is also used as mailbox, until released
> +        * by the OS.
> +        * The mechanism is similar to the DT enable-method = "spin-table", but works
> +        * with ACPI enabled platforms.
> +        */
> +       b       acpi_pp_secondary_jump
> +       /* never return */
>  #elif defined(CONFIG_ARMV8_MULTIENTRY)
>         branch_if_master x0, master_cpu
>
> --
> 2.46.0
>