linux-kernel - Re: [PATCH RFC v3 05/21] ACPI: Rename ACPI_HOTPLUG

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Message-ID: <CAJZ5v0g9nfLrEf9u4Ksw6BOWJQ9iv8Z-O8RsLU6jR5zk0ahxRw@mail.gmail.com>
Date: Mon, 18 Dec 2023 21:35:16 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Russell King <rmk+kernel@...linux.org.uk>
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, 
	acpica-devel@...ts.linuxfoundation.org, linux-csky@...r.kernel.org, 
	linux-doc@...r.kernel.org, linux-ia64@...r.kernel.org, 
	linux-parisc@...r.kernel.org, Salil Mehta <salil.mehta@...wei.com>, 
	Jean-Philippe Brucker <jean-philippe@...aro.org>, jianyong.wu@....com, justin.he@....com, 
	James Morse <james.morse@....com>
Subject: Re: [PATCH RFC v3 05/21] ACPI: Rename ACPI_HOTPLUG_CPU to include 'present'

On Wed, Dec 13, 2023 at 1:49 PM Russell King <rmk+kernel@...linux.org.uk> wrote:
>
> From: James Morse <james.morse@....com>
>
> The code behind ACPI_HOTPLUG_CPU allows a not-present CPU to become
> present.

Right.

> This isn't the only use of HOTPLUG_CPU. On arm64 and riscv
> CPUs can be taken offline as a power saving measure.

But still there is the case in which a non-present CPU can become
present, isn't it there?

> On arm64 an offline CPU may be disabled by firmware, preventing it from
> being brought back online, but it remains present throughout.
>
> Adding code to prevent user-space trying to online these disabled CPUs
> needs some additional terminology.
>
> Rename the Kconfig symbol CONFIG_ACPI_HOTPLUG_PRESENT_CPU to reflect
> that it makes possible CPUs present.

Honestly, I don't think that this change is necessary or even useful.