linux-kernel - Re: [PATCH] x86/acpi: Add acpi=spcr to use SPCR-provided default console

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Message-ID: <20260114154656.GDaWe6cFCruAGbJbhe@fat_crate.local>
Date: Wed, 14 Jan 2026 16:46:56 +0100
From: Borislav Petkov <bp@...en8.de>
To: Shenghao Yang <me@...nghaoyang.info>
Cc: x86@...nel.org, Jonathan Corbet <corbet@....net>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Len Brown <lenb@...nel.org>, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org
Subject: Re: [PATCH] x86/acpi: Add acpi=spcr to use SPCR-provided default
 console

On Sun, Dec 28, 2025 at 05:22:22PM +0800, Shenghao Yang wrote:
> Commit 0231d00082f6 ("ACPI: SPCR: Make SPCR available to x86")
> made SPCR available as an earlycon option on x86 but did not add
> it as a preferred console to avoid breaking existing setups -

No one has noticed AFAICT since 2018 (this commit's date).

Also:

        /* Do not enable ACPI SPCR console by default */
        acpi_parse_spcr(earlycon_acpi_spcr_enable, false);

Looks nicely conservative to me.

> users have to round trip the dumped console options
> ("SPCR: console: uart,io,0x3f8,115200") back via their
> bootloader.

I don't know what that means.

> Let users opt in so serial console configuration can be made
> automatic.

Why?

Text says:

	[X86] When used with no options the early console is
	determined by the ACPI SPCR table.

But the code doesn't enable the SPCR console by default.

I have no clue what this patch is trying to do.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette