linux-kernel - Re: [PATCH] ACPI: bus: Fix osc_sb_cppc_not

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Date:   Fri, 24 Jun 2022 18:11:35 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Perry Yuan <Perry.Yuan@....com>
Cc:     Huang Rui <Ray.Huang@....com>,
        Mario Limonciello <Mario.Limonciello@....com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Len Brown <lenb@...nel.org>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Nathan Fontenot <Nathan.Fontenot@....com>,
        "Su, Jinzhou (Joe)" <Jinzhou.Su@....com>, Xinmei.Huang@....com,
        "Du, Xiaojian" <Xiaojian.Du@....com>,
        "Meng, Li (Jassmine)" <Li.Meng@....com>,
        Linux PM <linux-pm@...r.kernel.org>
Subject: Re: [PATCH] ACPI: bus: Fix osc_sb_cppc_not_supported check

On Fri, Jun 24, 2022 at 2:00 PM Perry Yuan <Perry.Yuan@....com> wrote:
>
> The patch fixs the osc_sb_cppc_not_supported variable checking
> Otherwise the cppc acpi driver will be failed to register causing AMD
> pstate driver failed to load when calling acpi_cpc_valid()
>
> Fixes: c42fa24b447("ACPI: bus: Avoid using CPPC if not supported by firmware")
> Signed-off-by: Perry Yuan <Perry.Yuan@....com>
> ---
>  drivers/acpi/bus.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/acpi/bus.c b/drivers/acpi/bus.c
> index 4d7c51a33b01..9731e4a1e338 100644
> --- a/drivers/acpi/bus.c
> +++ b/drivers/acpi/bus.c
> @@ -359,7 +359,7 @@ static void acpi_bus_osc_negotiate_platform_control(void)
>         }
>
>  #ifdef CONFIG_ACPI_CPPC_LIB
> -       osc_sb_cppc_not_supported = !(capbuf_ret[OSC_SUPPORT_DWORD] &
> +       osc_sb_cppc_not_supported = !(capbuf_ret[OSC_SUPPORT_DWORD] &&
>                         (OSC_SB_CPC_SUPPORT | OSC_SB_CPCV2_SUPPORT));

This certainly is not a correct fix, because it causes
osc_sb_cppc_not_supported to always be true if
capbuf_ret[OSC_SUPPORT_DWORD] is not zero.

>  #endif
>
> --
> 2.25.1
>