linux-kernel - Re: [PATCH v3 1/2] x86/cpufeatures: Add AMD FAST CPPC feature flag

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Date: Thu, 23 May 2024 15:24:22 -0700
From: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
To: Xiaojian Du <Xiaojian.Du@....com>
Cc: linux-kernel@...r.kernel.org, x86@...nel.org, linux-pm@...r.kernel.org,
	tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
	dave.hansen@...ux.intel.com, hpa@...or.com,
	daniel.sneddon@...ux.intel.com, jpoimboe@...nel.org,
	sandipan.das@....com, kai.huang@...el.com, ray.huang@....com,
	rafael@...nel.org, Perry.Yuan@....com, gautham.shenoy@....com,
	Borislav.Petkov@....com, mario.limonciello@....com
Subject: Re: [PATCH v3 1/2] x86/cpufeatures: Add AMD FAST CPPC feature flag

On Thu, May 23, 2024 at 02:16:59PM +0800, Xiaojian Du wrote:
> From: Perry Yuan <perry.yuan@....com>
> 
> Some AMD Zen 4 processors support a new feature FAST CPPC which
> allows for a faster CPPC loop due to internal architectual

s/architectual/architectural/

> enhancements. The goal of this faster loop is higher performance
> at the same power consumption.
> 
> Reference:
> See the page 99 of PPR for AMD Family 19h Model 61h rev.B1, docID 56713
> 
> Signed-off-by: Perry Yuan <perry.yuan@....com>
> Signed-off-by: Xiaojian Du <Xiaojian.Du@....com>
> Reviewed-by: Borislav Petkov (AMD) <bp@...en8.de>
> ---
>  arch/x86/include/asm/cpufeatures.h | 1 +
>  arch/x86/kernel/cpu/scattered.c    | 1 +
>  2 files changed, 2 insertions(+)
> 
> diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
> index 3c7434329661..6c128d463a14 100644
> --- a/arch/x86/include/asm/cpufeatures.h
> +++ b/arch/x86/include/asm/cpufeatures.h
> @@ -470,6 +470,7 @@
>  #define X86_FEATURE_BHI_CTRL		(21*32+ 2) /* "" BHI_DIS_S HW control available */
>  #define X86_FEATURE_CLEAR_BHB_HW	(21*32+ 3) /* "" BHI_DIS_S HW control enabled */
>  #define X86_FEATURE_CLEAR_BHB_LOOP_ON_VMEXIT (21*32+ 4) /* "" Clear branch history at vmexit using SW loop */
> +#define X86_FEATURE_FAST_CPPC		(21*32 + 5) /* "" AMD Fast CPPC */
>  
>  /*
>   * BUG word(s)
> diff --git a/arch/x86/kernel/cpu/scattered.c b/arch/x86/kernel/cpu/scattered.c
> index af5aa2c754c2..9c273c231f56 100644
> --- a/arch/x86/kernel/cpu/scattered.c
> +++ b/arch/x86/kernel/cpu/scattered.c
> @@ -51,6 +51,7 @@ static const struct cpuid_bit cpuid_bits[] = {
>  	{ X86_FEATURE_PERFMON_V2,	CPUID_EAX,  0, 0x80000022, 0 },
>  	{ X86_FEATURE_AMD_LBR_V2,	CPUID_EAX,  1, 0x80000022, 0 },
>  	{ X86_FEATURE_AMD_LBR_PMC_FREEZE,	CPUID_EAX,  2, 0x80000022, 0 },
> +	{ X86_FEATURE_FAST_CPPC,	CPUID_EDX,  15, 0x80000007, 0 },
                                                  ^
						  Extra space here.