linux-kernel - Re: [PATCH v6 02/10] x86/acpi: Move acpi_wakeup

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Message-ID: <20251030054350.GA17477@ranerica-svr.sc.intel.com>
Date: Wed, 29 Oct 2025 22:43:50 -0700
From: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
To: Borislav Petkov <bp@...en8.de>
Cc: x86@...nel.org, Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>, Rob Herring <robh@...nel.org>,
	"K. Y. Srinivasan" <kys@...rosoft.com>,
	Haiyang Zhang <haiyangz@...rosoft.com>,
	Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>,
	Michael Kelley <mhklinux@...look.com>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Saurabh Sengar <ssengar@...ux.microsoft.com>,
	Chris Oo <cho@...rosoft.com>, "Kirill A. Shutemov" <kas@...nel.org>,
	linux-hyperv@...r.kernel.org, devicetree@...r.kernel.org,
	linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
	Ricardo Neri <ricardo.neri@...el.com>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Yunhong Jiang <yunhong.jiang@...ux.intel.com>
Subject: Re: [PATCH v6 02/10] x86/acpi: Move acpi_wakeup_cpu() and helpers to
 smpwakeup.c

On Wed, Oct 29, 2025 at 12:13:58PM +0100, Borislav Petkov wrote:
> On Mon, Oct 27, 2025 at 01:58:16PM -0700, Ricardo Neri wrote:
> > Right. All the functions in the file start with the acpi_ prefix. It could
> > be kept under arch/x86/kernel/acpi/. The Kconfig symbol X86_MAILBOX_WAKEUP
> > would have to live in arch/x86/Kconfig as there is no Kconfig file under
> > arch/x86/kernel/acpi. ACPI_MADT_WAKEUP is arch/x86/Kconfig.
> > 
> > Does that sound acceptable?
> 
> Right, this looks kinda weird. You have devicetree thing using ACPI code,
> you're trying to carve it out but then it is ACPI code anyway. So why even do
> that?
> 
> You can simply leave ACPI enabled on that configuration. I don't see yet what
> the point for the split is - saving memory, or...?

I did not want to enable the whole of ACPI code as I need a tiny portion of it.
Then yes, saving memory and having a smaller binary were considerations.

The only dependency that ACPI_MADT_WAKEUP has on ACPI is the code to read and
parse the ACPI table that enumerates the mailbox. (There are a couple of
declarations for CPU offlining that need tweaking if I want ACPI_MADT_WAKEUP to
not depend on ACPI at all).

The DeviceTree firmware only needs the code to wake CPUs up. That is the code
I am carving out.

Having said that, vmlinux and bzImage increase by 4% if I enable ACPI.

Thanks and BR,
Ricardo