linux-kernel - Re: [PATCH] ACPI: Do not enable ACPI SPCR console by default on arm64

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Date: Tue, 18 Jun 2024 16:29:24 +0100
From: Will Deacon <will@...nel.org>
To: Prarit Bhargava <prarit@...hat.com>, sudeep.holla@....com,
	lpieralisi@...nel.org, guohanjun@...wei.com
Cc: Liu Wei <liuwei09@...tc.cn>, catalin.marinas@....com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	liuwei09.cestc.cn@...loud.com, rafael@...nel.org
Subject: Re: [PATCH] ACPI: Do not enable ACPI SPCR console by default on arm64

On Thu, May 30, 2024 at 09:06:17AM -0400, Prarit Bhargava wrote:
> On 5/29/24 21:53, Liu Wei wrote:
> > Consistency with x86 and loongarch, don't enable ACPI SPCR console
> > by default on arm64
> > 
> > Signed-off-by: Liu Wei <liuwei09@...tc.cn>
> > ---
> >   arch/arm64/kernel/acpi.c | 3 ++-
> >   1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > diff --git a/arch/arm64/kernel/acpi.c b/arch/arm64/kernel/acpi.c
> > index dba8fcec7f33..1deda3e5a0d2 100644
> > --- a/arch/arm64/kernel/acpi.c
> > +++ b/arch/arm64/kernel/acpi.c
> > @@ -227,7 +227,8 @@ void __init acpi_boot_table_init(void)
> >   		if (earlycon_acpi_spcr_enable)
> >   			early_init_dt_scan_chosen_stdout();
> >   	} else {
> > -		acpi_parse_spcr(earlycon_acpi_spcr_enable, true);
> > +		/* Do not enable ACPI SPCR console by default */
> > +		acpi_parse_spcr(earlycon_acpi_spcr_enable, false);
> >   		if (IS_ENABLED(CONFIG_ACPI_BGRT))
> >   			acpi_table_parse(ACPI_SIG_BGRT, acpi_parse_bgrt);
> >   	}
> 
> It's been a while, and the status of arm hardware may have changed. IIRC the
> choice to force enable this is that most arm hardware is headless and this
> was a _required_ option for booting.
> 
> I'm not sure if that's still the case as it's been a long time.
> 
> Can anyone from the ARM community provide an approval here?

I don't have a strong opinion either way, but adding the Arm ACPI folks
in case they care.

Having said that, if the only rationale for this patch is consistency
with other architectures, then I think I'd lean towards leaving the
behaviour as-is so we don't give users a nasty surprise on their next
kernel upgrade.

Will