Re: [PATCH v12 4/9] cpufreq: amd-pstate: initialize new core precision boost state

[Mario Limonciello]

On 6/19/2024 04:16, Perry Yuan wrote:
> From: Perry Yuan <Perry.Yuan@xxxxxxx>
>
> Add one global `global_params` to represent CPU Performance Boost(cpb)
> state for cpu frequency scaling, both active and passive modes all can
> support CPU cores frequency boosting control which is based on the BIOS
> setting, while BIOS turn on the "Core Performance Boost", it will
> allow OS control each core highest perf limitation from OS side.
>
> The active, guided and passive modes of the amd-pstate driver can
> support frequency boost control when the "Core Performance Boost"
> (CPB) feature is enabled in the BIOS.  When enabled in BIOS, the user
> has an option at runtime to allow/disallow the cores from operating in
> the boost frequency range.
>
> Add an amd_pstate_global_params object to record whether CPB is
> enabled in BIOS, and if it has been activated by the user
>
> Reported-by: Artem S. Tashkinov" <aros@xxxxxxx>
> Cc: Oleksandr Natalenko <oleksandr@xxxxxxxxxxxxxx>
> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=217931
> Signed-off-by: Perry Yuan <Perry.Yuan@xxxxxxx>
> ---
>   drivers/cpufreq/amd-pstate.c | 59 +++++++++++++++++++++++++++++-------
>   drivers/cpufreq/amd-pstate.h | 13 ++++++++
>   2 files changed, 61 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> index 5bdcdd3ea163..0c50b8ba16b6 100644
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -102,6 +102,8 @@ static int cppc_state = AMD_PSTATE_UNDEFINED;
>   static bool cppc_enabled;
>   static bool amd_pstate_prefcore = true;
>   static struct quirk_entry *quirks;
> +struct amd_pstate_global_params amd_pstate_global_params;
> +EXPORT_SYMBOL_GPL(amd_pstate_global_params);
>   
>   /*
>    * AMD Energy Preference Performance (EPP)
> @@ -694,7 +696,7 @@ static int amd_pstate_set_boost(struct cpufreq_policy *policy, int state)
>   
>   	if (!cpudata->boost_supported) {
>   		pr_err("Boost mode is not supported by this processor or SBIOS\n");
> -		return -EINVAL;
> +		return -ENOTSUPP;

You're using -ENOTSUPP here and -EOPNOTSUPP in amd_pstate_boost_set(). 
You should be consistent with these error codes.  That being said I 
think the other error flow needs to go.  More on that below.

>   	}
>   
>   	if (state)
> @@ -712,18 +714,38 @@ static int amd_pstate_set_boost(struct cpufreq_policy *policy, int state)
>   	return 0;
>   }
>   
> -static void amd_pstate_boost_init(struct amd_cpudata *cpudata)
> +static int amd_pstate_boost_set(struct amd_cpudata *cpudata)
>   {
> -	u32 highest_perf, nominal_perf;
> +	u64 boost_val;
> +	int ret = -1;
>   
> -	highest_perf = READ_ONCE(cpudata->highest_perf);
> -	nominal_perf = READ_ONCE(cpudata->nominal_perf);
> +	if (!cpu_feature_enabled(X86_FEATURE_CPB)) {
> +		pr_debug_once("Boost CPB capabilities not present in the processor\n");
> +		ret = -EOPNOTSUPP;
> +		goto exit_err;
> +	}

This needs a little bit of unwinding to think about whether it's correct 
return code.

This is the call path:

cpufreq_driver->init_boost();
-> amd_pstate_init_boost()
->-> amd_pstate_boost_set()

So if we end up with a platform that supports CPPC but doesn't support 
boost we might end up nuking the amd-pstate support "because" of the 
lack of boost.

For this reason I think it's better to set the return code to 0 in this 
specific place.  The others in this function look correct to me and if 
fail should cause a critical problem with setting up CPPC.

>   
> -	if (highest_perf <= nominal_perf)
> -		return;
> +	ret = rdmsrl_on_cpu(cpudata->cpu, MSR_K7_HWCR, &boost_val);
> +	if (ret) {
> +		pr_err_once("failed to read initial CPU boost state!\n");
> +		ret = -EIO;
> +		goto exit_err;
> +	}
> +
> +	amd_pstate_global_params.cpb_supported = !(boost_val & MSR_K7_HWCR_CPB_DIS);
> +	if (amd_pstate_global_params.cpb_supported) {
> +		current_pstate_driver->boost_enabled = true;
> +		WRITE_ONCE(cpudata->boost_supported, true);
> +	}
>   
> -	cpudata->boost_supported = true;
> -	current_pstate_driver->boost_enabled = true;
> +	amd_pstate_global_params.cpb_boost = amd_pstate_global_params.cpb_supported;
> +	return 0;
> +
> +exit_err:
> +	WRITE_ONCE(cpudata->boost_supported, false);
> +	current_pstate_driver->boost_enabled = false;
> +	amd_pstate_global_params.cpb_boost = false;
> +	return ret;
>   }
>   
>   static void amd_perf_ctl_reset(unsigned int cpu)
> @@ -1005,7 +1027,6 @@ static int amd_pstate_cpu_init(struct cpufreq_policy *policy)
>   
>   	policy->driver_data = cpudata;
>   
> -	amd_pstate_boost_init(cpudata);
>   	if (!current_pstate_driver->adjust_perf)
>   		current_pstate_driver->adjust_perf = amd_pstate_adjust_perf;
>   
> @@ -1387,6 +1408,21 @@ static bool amd_pstate_acpi_pm_profile_undefined(void)
>   	return false;
>   }
>   
> +static int amd_pstate_init_boost(struct cpufreq_policy *policy)
> +{
> +	struct amd_cpudata *cpudata = policy->driver_data;
> +	int ret;
> +
> +	/* initialize cpu cores boot state */
> +	ret = amd_pstate_boost_set(cpudata);
> +	if (ret)
> +		return ret;
> +
> +	policy->boost_enabled = READ_ONCE(cpudata->boost_supported);
> +
> +	return 0;
> +}
> +
>   static int amd_pstate_epp_cpu_init(struct cpufreq_policy *policy)
>   {
>   	int min_freq, max_freq, nominal_freq, ret;
> @@ -1465,7 +1501,6 @@ static int amd_pstate_epp_cpu_init(struct cpufreq_policy *policy)
>   			return ret;
>   		WRITE_ONCE(cpudata->cppc_cap1_cached, value);
>   	}
> -	amd_pstate_boost_init(cpudata);
>   
>   	return 0;
>   
> @@ -1704,6 +1739,7 @@ static struct cpufreq_driver amd_pstate_driver = {
>   	.exit		= amd_pstate_cpu_exit,
>   	.suspend	= amd_pstate_cpu_suspend,
>   	.resume		= amd_pstate_cpu_resume,
> +	.init_boost	= amd_pstate_init_boost,
>   	.set_boost	= amd_pstate_set_boost,
>   	.update_limits	= amd_pstate_update_limits,
>   	.name		= "amd-pstate",
> @@ -1721,6 +1757,7 @@ static struct cpufreq_driver amd_pstate_epp_driver = {
>   	.suspend	= amd_pstate_epp_suspend,
>   	.resume		= amd_pstate_epp_resume,
>   	.update_limits	= amd_pstate_update_limits,
> +	.init_boost	= amd_pstate_init_boost,
>   	.name		= "amd-pstate-epp",
>   	.attr		= amd_pstate_epp_attr,
>   };
> diff --git a/drivers/cpufreq/amd-pstate.h b/drivers/cpufreq/amd-pstate.h
> index f80b33fa5d43..133042370a8f 100644
> --- a/drivers/cpufreq/amd-pstate.h
> +++ b/drivers/cpufreq/amd-pstate.h
> @@ -102,4 +102,17 @@ struct amd_cpudata {
>   	s16	epp_default;
>   };
>   
> +/**
> + * struct amd_pstate_global_params - Global parameters, mostly tunable via sysfs.
> + * @cpb_boost:		Whether or not to use boost CPU P-states.
> + * @cpb_supported:	Whether or not CPU boost P-states are available
> + *			based on the MSR_K7_HWCR bit[25] state
> + */
> +struct amd_pstate_global_params {
> +	bool cpb_boost;
> +	bool cpb_supported;
> +};
> +
> +extern struct amd_pstate_global_params amd_pstate_global_params;
> +
>   #endif /* _LINUX_AMD_PSTATE_H */