Received-SPF: pass (google.com: domain of linux-kernel+bounces-4361-linux.lists.archive=gmail.com@vger.kernel.org designates 139.178.88.99 as permitted sender) client-ip=139.178.88.99;
Precedence: bulk
MIME-Version: 1.0
References: <ZXmn46ptis59F0CO@shell.armlinux.org.uk> <E1rDOgD-00Dvk2-3h@rmk-PC.armlinux.org.uk>
In-Reply-To: <E1rDOgD-00Dvk2-3h@rmk-PC.armlinux.org.uk>
From: "Rafael J. Wysocki" <rafael@kernel.org>
Date: Mon, 18 Dec 2023 21:35:16 +0100
Message-ID: <CAJZ5v0g9nfLrEf9u4Ksw6BOWJQ9iv8Z-O8RsLU6jR5zk0ahxRw@mail.gmail.com>
Subject: Re: [PATCH RFC v3 05/21] ACPI: Rename ACPI_HOTPLUG_CPU to include 'present'
To: Russell King <rmk+kernel@armlinux.org.uk>
Cc: linux-pm@vger.kernel.org, loongarch@lists.linux.dev, 
	linux-acpi@vger.kernel.org, linux-arch@vger.kernel.org, 
	linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, 
	linux-riscv@lists.infradead.org, kvmarm@lists.linux.dev, x86@kernel.org, 
	acpica-devel@lists.linuxfoundation.org, linux-csky@vger.kernel.org, 
	linux-doc@vger.kernel.org, linux-ia64@vger.kernel.org, 
	linux-parisc@vger.kernel.org, Salil Mehta <salil.mehta@huawei.com>, 
	Jean-Philippe Brucker <jean-philippe@linaro.org>, jianyong.wu@arm.com, justin.he@arm.com, 
	James Morse <james.morse@arm.com>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

On Wed, Dec 13, 2023 at 1:49=E2=80=AFPM Russell King <rmk+kernel@armlinux.o=
rg.uk> wrote:
>
> From: James Morse <james.morse@arm.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.