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From:   "Rafael J. Wysocki" <rafael@kernel.org>
Date:   Wed, 1 Apr 2020 11:11:48 +0200
Message-ID: <CAJZ5v0iMJYG1ptdoeiHVo21NqhWBVPw691LJ5=3oRMA7OMQ91Q@mail.gmail.com>
Subject: Re: [PATCH] acpica: clear global_lock bits at FACS initialization
To:     Jan Engelhardt <jengelh@inai.de>,
        Erik Kaneda <erik.kaneda@intel.com>,
        Robert Moore <robert.moore@intel.com>
Cc:     Rafael Wysocki <rafael.j.wysocki@intel.com>,
        ACPI Devel Maling List <linux-acpi@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Mon, Mar 30, 2020 at 10:58 AM Jan Engelhardt <jengelh@inai.de> wrote:
>
> When the firmware ROM supplies a FACS table with garbage, and the
> firmware code does not clear the global_lock field before booting to a
> loader/OS, the garbage bytes in that field (like 0xffffffff) can
> indicate that the lock is taken when it is not, thereby preventing
> obtaining said lock even though it is otherwise perfectly usable if
> the field were not prepopulated with garbage.
>
> Reset the lock to a known good state upon ACPI initialization.
>
> References: https://bugzilla.kernel.org/show_bug.cgi?id=206553
> Signed-off-by: Jan Engelhardt <jengelh@inai.de>

Bob, Erik, please let me know if you want me to apply this directly or
you prefer to route it through the upstream.

> ---
>
>  drivers/acpi/acpica/tbutils.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/drivers/acpi/acpica/tbutils.c b/drivers/acpi/acpica/tbutils.c
> index c5f0b8ec70cc..26bdbc585d7e 100644
> --- a/drivers/acpi/acpica/tbutils.c
> +++ b/drivers/acpi/acpica/tbutils.c
> @@ -56,6 +56,9 @@ acpi_status acpi_tb_initialize_facs(void)
>                                                                      &facs));
>                 acpi_gbl_FACS = facs;
>         }
> +       /* Clear potential garbage from the initial FACS table. */
> +       if (facs != NULL)
> +               facs->global_lock &= ~0x3;
>
>         /* If there is no FACS, just continue. There was already an error msg */
>
> --
> 2.26.0
>