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

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Message-ID: <5c14a151-25c9-41f5-af65-d2a8ffe548fa@intel.com>
Date: Thu, 23 May 2024 09:31:51 -0700
From: Dave Hansen <dave.hansen@...el.com>
To: Xiaojian Du <Xiaojian.Du@....com>, linux-kernel@...r.kernel.org,
 x86@...nel.org, linux-pm@...r.kernel.org
Cc: 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, pawan.kumar.gupta@...ux.intel.com,
 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 5/22/24 23:16, Xiaojian Du wrote:
>  #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 */

It'd be nice to expand the CPPC acronym at least _once_.

Also, this is used _once_ at boot and not exposed in /proc/cpuinfo.  Is
it even worth defining an X86_FEATURE_ for it?