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

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Message-ID: <20240523223501.k2bcmvmfbvbxiuf6@desk>
Date: Thu, 23 May 2024 15:35:01 -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
> 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 },

This list is sorted by the leaf level, so position of this entry should be
higher:

diff --git a/arch/x86/kernel/cpu/scattered.c b/arch/x86/kernel/cpu/scattered.c
index af5aa2c754c2..09e0e40dce6c 100644
--- a/arch/x86/kernel/cpu/scattered.c
+++ b/arch/x86/kernel/cpu/scattered.c
@@ -45,6 +45,7 @@ static const struct cpuid_bit cpuid_bits[] = {
 	{ X86_FEATURE_HW_PSTATE,	CPUID_EDX,  7, 0x80000007, 0 },
 	{ X86_FEATURE_CPB,		CPUID_EDX,  9, 0x80000007, 0 },
 	{ X86_FEATURE_PROC_FEEDBACK,    CPUID_EDX, 11, 0x80000007, 0 },
+	{ X86_FEATURE_FAST_CPPC,	CPUID_EDX, 15, 0x80000007, 0 },
 	{ X86_FEATURE_MBA,		CPUID_EBX,  6, 0x80000008, 0 },
 	{ X86_FEATURE_SMBA,		CPUID_EBX,  2, 0x80000020, 0 },
 	{ X86_FEATURE_BMEC,		CPUID_EBX,  3, 0x80000020, 0 },

>  	{ 0, 0, 0, 0, 0 }
>  };
>  
> -- 
> 2.34.1
>