linux-kernel - Re: [PATCH v4 04/11] cpufreq: amd-pstate: add debug message while CPPC is supported and disabled by SBIOS

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Date: Tue, 18 Jun 2024 14:25:08 -0500
From: Mario Limonciello <mario.limonciello@....com>
To: Perry Yuan <perry.yuan@....com>, rafael.j.wysocki@...el.com,
 viresh.kumar@...aro.org, Ray.Huang@....com, gautham.shenoy@....com,
 Borislav.Petkov@....com
Cc: Alexander.Deucher@....com, Xinmei.Huang@....com, Xiaojian.Du@....com,
 Li.Meng@....com, linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 04/11] cpufreq: amd-pstate: add debug message while
 CPPC is supported and disabled by SBIOS

On 6/17/2024 01:59, Perry Yuan wrote:
> If CPPC feature is supported by the CPU however the CPUID flag bit is not
> set by SBIOS, the `amd_pstate` will be failed to load while system
> booting.
> So adding one more debug message to inform user to check the SBIOS setting,
> The change also can help maintainers to debug why amd_pstate driver failed
> to be loaded at system booting if the processor support CPPC.
> 
> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=218686
> Signed-off-by: Perry Yuan <perry.yuan@....com>
> Reviewed-by: Gautham R. Shenoy <gautham.shenoy@....com>

Acked-by: Mario Limonciello <mario.limonciello@....com>

> ---
>   drivers/cpufreq/amd-pstate.c | 26 ++++++++++++++++++++++++++
>   1 file changed, 26 insertions(+)
> 
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> index 76419762c04f..9aa220a0e3fe 100644
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -1749,11 +1749,37 @@ static int __init amd_pstate_set_driver(int mode_idx)
>    */
>   static bool amd_cppc_supported(void)
>   {
> +	struct cpuinfo_x86 *c = &cpu_data(0);
> +	bool warn = false;
> +
>   	if ((boot_cpu_data.x86 == 0x17) && (boot_cpu_data.x86_model < 0x30)) {
>   		pr_debug_once("CPPC feature is not supported by the processor\n");
>   		return false;
>   	}
>   
> +	/*
> +	 * 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 (!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)
> +				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))
> +				warn = true;
> +		} else if (cpu_feature_enabled(X86_FEATURE_ZEN5)) {
> +			warn = true;
> +		}
> +	}
> +
> +	if (warn)
> +		pr_warn_once("The CPPC feature is supported but currently disabled by the BIOS.\n"
> +					"Please enable it if your BIOS has the CPPC option.\n");
>   	return true;
>   }
>