linux-kernel - Re: New warning: ACPI: CEDT not present

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Date:   Tue, 15 Feb 2022 18:11:02 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     Paul Menzel <pmenzel@...gen.mpg.de>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Linux ACPI <linux-acpi@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>, regressions@...ts.linux.dev
Subject: Re: New warning: ACPI: CEDT not present

On Tue, Feb 15, 2022 at 5:22 PM Dan Williams <dan.j.williams@...el.com> wrote:
>
> On Mon, Feb 14, 2022 at 11:52 PM Paul Menzel <pmenzel@...gen.mpg.de> wrote:
> >
> > #regzbot introduced: 2d03e46a4bad20191d07b83ec1242d5f002577be
> >
> > Dear Dan,
> >
> >
> > On the Dell Latitude E7250, Linux 5.17-rc3 logs the warning below
> > (`dmesg --level=warn`):
> >
> >      ACPI: CEDT not present
> >
> > I think commit 2d03e46a4bad (ACPI: Add a context argument for table
> > parsing handlers), part of Linux since 5.17-rc1, is the reason.
> >
> > If I understand it correctly, CEDT is not to be expected on older
> > devices, so the warning is not justified. Can something be done about it?
>
> Rafael,
>
> I'm inclined to just delete the warning altogether, but special casing
> is also an option. Any preference?

Change it into pr_debug()?

> diff --git a/drivers/acpi/tables.c b/drivers/acpi/tables.c
> index 0741a4933f62..fb2e4a216154 100644
> --- a/drivers/acpi/tables.c
> +++ b/drivers/acpi/tables.c
> @@ -399,7 +399,7 @@ int __init_or_acpilib acpi_table_parse_entries_array(
>                 instance = acpi_apic_instance;
>
>         acpi_get_table(id, instance, &table_header);
> -       if (!table_header) {
> +       if (!table_header && strcmp(id, ACPI_SIG_CEDT) != 0) {
>                 pr_warn("%4.4s not present\n", id);
>                 return -ENODEV;
>         }