linux-kernel - Re: [PATCH v2 1/1] cpufreq/amd-pstate: Remove warning for X86_FEATURE

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Message-ID: <69111390-dad9-429f-bfa7-79916d384c69@amd.com>
Date: Wed, 28 Aug 2024 10:14:07 -0500
From: Mario Limonciello <mario.limonciello@....com>
To: "Gautham R. Shenoy" <gautham.shenoy@....com>,
 "Rafael J . Wysocki" <rafael@...nel.org>,
 Viresh Kumar <viresh.kumar@...aro.org>
Cc: linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
 Huang Rui <ray.huang@....com>, Perry Yuan <perry.yuan@....com>,
 Dhananjay Ugwekar <Dhananjay.Ugwekar@....com>, David Wang
 <00107082@....com>, Xiaojian Du <xiaojian.du@....com>
Subject: Re: [PATCH v2 1/1] cpufreq/amd-pstate: Remove warning for
 X86_FEATURE_CPPC on certain Zen models

On 8/28/2024 05:10, Gautham R. Shenoy wrote:
> commit bff7d13c190a ("cpufreq: amd-pstate: add debug message while
> CPPC is supported and disabled by SBIOS") issues a warning on plaforms
> where the X86_FEATURE_CPPC is expected to be enabled, but is not due
> to it being disabled in the BIOS.
> 
> This feature bit corresponds to CPUID 0x80000008.ebx[27] which is a
> reserved bit on the Zen1 processors and a reserved bit on Zen2 based
> models 0x70-0x7F, and is expected to be cleared on these
> platforms. Thus printing the warning message for these models when
> X86_FEATURE_CPPC is unavailable is incorrect. Fix this.
> 
> Modify some of the comments, and use switch-case for model range
> checking for improved readability while at it.
> 
> Fixes: bff7d13c190a ("cpufreq: amd-pstate: add debug message while CPPC is supported and disabled by SBIOS")
> Cc: Xiaojian Du <xiaojian.du@....com>
> Reported-by: David Wang <00107082@....com>
> Closes: https://lore.kernel.org/lkml/20240730140111.4491-1-00107082@163.com/
> Signed-off-by: Gautham R. Shenoy <gautham.shenoy@....com>

Thanks!

Acked-by: Mario Limonciello <mario.limonciello@....com>
Will apply to fixes branch.

> ---
>   drivers/cpufreq/amd-pstate.c | 34 ++++++++++++++++++++++++----------
>   1 file changed, 24 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> index 89bda7a2bb8d..259a917da75f 100644
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -1834,20 +1834,34 @@ static bool amd_cppc_supported(void)
>   	}
>   
>   	/*
> -	 * If the CPPC feature is disabled in the BIOS for processors that support MSR-based CPPC,
> -	 * the AMD Pstate driver may not function correctly.
> -	 * Check the CPPC flag and display a warning message if the platform supports CPPC.
> -	 * Note: below checking code will not abort the driver registeration process because of
> -	 * the code is added for debugging purposes.
> +	 * If the CPPC feature is disabled in the BIOS for processors
> +	 * that support MSR-based CPPC, the AMD Pstate driver may not
> +	 * function correctly.
> +	 *
> +	 * For such processors, check the CPPC flag and display a
> +	 * warning message if the platform supports CPPC.
> +	 *
> +	 * Note: The code check below will not abort the driver
> +	 * registration process because of the code is added for
> +	 * debugging purposes. Besides, it may still be possible for
> +	 * the driver to work using the shared-memory mechanism.
>   	 */
>   	if (!cpu_feature_enabled(X86_FEATURE_CPPC)) {
> -		if (cpu_feature_enabled(X86_FEATURE_ZEN1) || cpu_feature_enabled(X86_FEATURE_ZEN2)) {
> -			if (c->x86_model > 0x60 && c->x86_model < 0xaf)
> +		if (cpu_feature_enabled(X86_FEATURE_ZEN2)) {
> +			switch (c->x86_model) {
> +			case 0x60 ... 0x6F:
> +			case 0x80 ... 0xAF:
>   				warn = true;
> -		} else if (cpu_feature_enabled(X86_FEATURE_ZEN3) || cpu_feature_enabled(X86_FEATURE_ZEN4)) {
> -			if ((c->x86_model > 0x10 && c->x86_model < 0x1F) ||
> -					(c->x86_model > 0x40 && c->x86_model < 0xaf))
> +				break;
> +			}
> +		} else if (cpu_feature_enabled(X86_FEATURE_ZEN3) ||
> +			   cpu_feature_enabled(X86_FEATURE_ZEN4)) {
> +			switch (c->x86_model) {
> +			case 0x10 ... 0x1F:
> +			case 0x40 ... 0xAF:
>   				warn = true;
> +				break;
> +			}
>   		} else if (cpu_feature_enabled(X86_FEATURE_ZEN5)) {
>   			warn = true;
>   		}