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

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Message-ID: <CAPcyv4jSP4PTehMdkcpZfpDcz1HZ0ekjx+WztOiqpwGFU-1iBg@mail.gmail.com>
Date:   Tue, 15 Feb 2022 08:22:02 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     Paul Menzel <pmenzel@...gen.mpg.de>
Cc:     "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 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?

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;
        }