linux-kernel - Re: [PATCH 1/2] x86/cpu/amd: Clarify amd_get_highest

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Date: Wed, 26 Jun 2024 19:14:21 +0200
From: Borislav Petkov <bp@...en8.de>
To: Mario Limonciello <mario.limonciello@....com>
Cc: "Gautham R . Shenoy" <gautham.shenoy@....com>,
	Perry Yuan <perry.yuan@....com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
	"H . Peter Anvin" <hpa@...or.com>, Huang Rui <ray.huang@....com>,
	"Rafael J . Wysocki" <rafael@...nel.org>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Nikolay Borisov <nik.borisov@...e.com>,
	Peter Zijlstra <peterz@...radead.org>,
	"open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <linux-kernel@...r.kernel.org>,
	"open list:AMD PSTATE DRIVER" <linux-pm@...r.kernel.org>
Subject: Re: [PATCH 1/2] x86/cpu/amd: Clarify amd_get_highest_perf()

On Tue, Jun 25, 2024 at 11:20:42PM -0500, Mario Limonciello wrote:
>  static inline int rdmsrl_amd_safe(unsigned msr, unsigned long long *p)
>  {
>  	u32 gprs[8] = { 0 };
> @@ -1194,15 +1198,27 @@ u32 amd_get_highest_perf(void)
>  {
>  	struct cpuinfo_x86 *c = &boot_cpu_data;
>  
> -	if (c->x86 == 0x17 && ((c->x86_model >= 0x30 && c->x86_model < 0x40) ||
> -			       (c->x86_model >= 0x70 && c->x86_model < 0x80)))
> -		return 166;
> +	if (cpu_feature_enabled(X86_FEATURE_ZEN2)) {
> +		switch (c->x86_model) {
> +		case 0x30 ... 0x40:
> +		case 0x70 ... 0x80:

Well, it was < 0x40 and < 0x80

You're making it <=.

> +			return CPPC_HIGHEST_PERF_DEFAULT;
> +		default:
> +			return CPPC_HIGHEST_PERF_MAX;
> +		}
> +	}
>  
> -	if (c->x86 == 0x19 && ((c->x86_model >= 0x20 && c->x86_model < 0x30) ||
> -			       (c->x86_model >= 0x40 && c->x86_model < 0x70)))
> -		return 166;
> +	if (cpu_feature_enabled(X86_FEATURE_ZEN3)) {
> +		switch (c->x86_model) {
> +		case 0x20 ... 0x30:
> +		case 0x40 ... 0x70:

Ditto.

Also, ontop:

diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index 73559db78433..5d496de4e141 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -1204,7 +1204,7 @@ u32 amd_get_highest_perf(void)
 		case 0x70 ... 0x80:
 			return CPPC_HIGHEST_PERF_DEFAULT;
 		default:
-			return CPPC_HIGHEST_PERF_MAX;
+			break;
 		}
 	}
 
@@ -1214,7 +1214,7 @@ u32 amd_get_highest_perf(void)
 		case 0x40 ... 0x70:
 			return CPPC_HIGHEST_PERF_DEFAULT;
 		default:
-			return CPPC_HIGHEST_PERF_MAX;
+			break;
 		}
 	}
 
so that you don't have so many redundant returns in the function.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette