linux-kernel - Re: [PATCH] x86/cstate: Replace vendor check with X86_FEATURE_MWAIT in ffh_cstate

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Date:   Tue, 5 Jul 2022 20:45:13 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Tony W Wang-oc <TonyWWang-oc@...oxin.com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        CobeChen@...oxin.com, TimGuo@...oxin.com, LindaChai@...oxin.com,
        LeoLiu@...oxin.com
Subject: Re: [PATCH] x86/cstate: Replace vendor check with X86_FEATURE_MWAIT
 in ffh_cstate_init

On Fri, Jul 1, 2022 at 9:05 AM Tony W Wang-oc <TonyWWang-oc@...oxin.com> wrote:
>
> The original commit 991528d73486 ("ACPI: Processor native C-states using
> MWAIT") has a vendor check for Intel in the function of ffh_cstate_init().
>
> Commit 5209654a46ee ("x86/ACPI/cstate: Allow ACPI C1 FFH MWAIT use on AMD
> systems") and commit 280b68a3b3b9 ("x86/cstate: Allow ACPI C1 FFH MWAIT
> use on Hygon systems") add vendor check for AMD and HYGON in the function
> of ffh_cstate_init().
>
> Recent Zhaoxin and Centaur CPUs support MONITOR/MWAIT instructions that
> can be used for ACPI Cx state in the same way as Intel. So expected to
> add the support of these CPUs in the function of ffh_cstate_init() too.
>
> The CPU feature X86_FEATURE_MWAIT indicates processor supports MONITOR/
> MWAIT instructions. So the check for many CPU vendors in ffh_cstate_init()
> is unnecessary, use X86_FEATURE_MWAIT to replace the CPU vendor check.
>
> Signed-off-by: Tony W Wang-oc <TonyWWang-oc@...oxin.com>

Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

or please let me know if I'm expected to pick up this one.  Thanks!


> ---
>  arch/x86/kernel/acpi/cstate.c | 6 +-----
>  1 file changed, 1 insertion(+), 5 deletions(-)
>
> diff --git a/arch/x86/kernel/acpi/cstate.c b/arch/x86/kernel/acpi/cstate.c
> index 7945eae..a64c38f 100644
> --- a/arch/x86/kernel/acpi/cstate.c
> +++ b/arch/x86/kernel/acpi/cstate.c
> @@ -209,11 +209,7 @@ EXPORT_SYMBOL_GPL(acpi_processor_ffh_cstate_enter);
>
>  static int __init ffh_cstate_init(void)
>  {
> -       struct cpuinfo_x86 *c = &boot_cpu_data;
> -
> -       if (c->x86_vendor != X86_VENDOR_INTEL &&
> -           c->x86_vendor != X86_VENDOR_AMD &&
> -           c->x86_vendor != X86_VENDOR_HYGON)
> +       if (!boot_cpu_has(X86_FEATURE_MWAIT))
>                 return -1;
>
>         cpu_cstate_entry = alloc_percpu(struct cstate_entry);
> --
> 2.7.4
>