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Date:   Thu, 23 Jun 2022 08:55:42 -0700
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Subject: Re: [PATCH V1] x86/cstate: Add Zhaoxin/Centaur ACPI Cx FFH MWAIT
 support
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To:     Tony W Wang-oc <TonyWWang-oc@zhaoxin.com>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Len Brown <len.brown@intel.com>, Pavel Machek <pavel@ucw.cz>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        the arch/x86 maintainers <x86@kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Linux PM <linux-pm@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Cc:     CobeChen@zhaoxin.com, TimGuo@zhaoxin.com, LindaChai@zhaoxin.com,
        LeoLiu@zhaoxin.com,
        ACPI Devel Maling List <linux-acpi@vger.kernel.org>
References: <0b583b7e-dcd3-be51-f367-1c12ac841d3f@zhaoxin.com>
From:   Dave Hansen <dave.hansen@intel.com>
In-Reply-To: <0b583b7e-dcd3-be51-f367-1c12ac841d3f@zhaoxin.com>
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On 6/22/22 18:26, Tony W Wang-oc wrote:
> Recent Zhaoxin/Centaur CPUs support X86_FEATURE_MWAIT that implies
> the MONITOR/MWAIT instructions can be used for ACPI Cx state.
> The BIOS declares Cx state in _CST object to use FFH on Zhaoxin/Centaur
> systems. So let function ffh_cstate_init() support These CPUs too.
> 
> Signed-off-by: Tony W Wang-oc <TonyWWang-oc@zhaoxin.com>
> ---
>  arch/x86/kernel/acpi/cstate.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/acpi/cstate.c b/arch/x86/kernel/acpi/cstate.c
> index 7945eae..d4185e1 100644
> --- a/arch/x86/kernel/acpi/cstate.c
> +++ b/arch/x86/kernel/acpi/cstate.c
> @@ -213,7 +213,9 @@ static int __init ffh_cstate_init(void)
> 
>      if (c->x86_vendor != X86_VENDOR_INTEL &&
>          c->x86_vendor != X86_VENDOR_AMD &&
> -        c->x86_vendor != X86_VENDOR_HYGON)
> +        c->x86_vendor != X86_VENDOR_HYGON &&
> +        c->x86_vendor != X86_VENDOR_CENTAUR &&
> +        c->x86_vendor != X86_VENDOR_ZHAOXIN)
>          return -1;

Many of the changelogs that add new vendors here go on about particular
C states declared in the _CST object and contents of CPUID leaf 5.

Why do we even _have_ a vendor check here?  Shouldn't the code just be
going and doing the validation of the _CST object and CPUID that the
changelogs blather on about?

Intel certainly made the original sin on this one (see 991528d7348), but
I hope _something_ changed in the 16 years since that patch went in.