linux-kernel - Re: [PATCH v7 3/6] cpufreq:amd-pstate: get pstate transition delay and latency value from ACPI tables

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Date: Thu, 14 Mar 2024 11:53:45 +0530
From: "Gautham R. Shenoy" <gautham.shenoy@....com>
To: Perry Yuan <perry.yuan@....com>
Cc: rafael.j.wysocki@...el.com, Mario.Limonciello@....com,
	viresh.kumar@...aro.org, Ray.Huang@....com, Borislav.Petkov@....com,
	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 v7 3/6] cpufreq:amd-pstate: get pstate transition delay
 and latency value from ACPI tables


On Wed, Mar 13, 2024 at 05:59:15PM +0800, Perry Yuan wrote:
> make pstate driver initially retrieve the P-state transition delay and latency
> values from the BIOS ACPI tables which has more reasonable delay and latency
> values according to the platform design and requirements.
> 
> Previously there values were hardcoded at specific value which may
> have conflicted with platform and it might not reflect the most accurate or
> optimized setting for the processor.
> 
> [054h 0084   8]                Preserve Mask : FFFFFFFF00000000
> [05Ch 0092   8]                   Write Mask : 0000000000000001
> [064h 0100   4]              Command Latency : 00000FA0
> [068h 0104   4]          Maximum Access Rate : 0000EA60
> [06Ch 0108   2]      Minimum Turnaround Time : 0000
> 
> Reviewed-by: Mario Limonciello <mario.limonciello@....com>
> Signed-off-by: Perry Yuan <perry.yuan@....com>

Looks good to me.

Reviewed-by: Gautham R. Shenoy <gautham.shenoy@....com>

> ---
>  drivers/cpufreq/amd-pstate.c | 34 ++++++++++++++++++++++++++++++++--
>  1 file changed, 32 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> index 6db9256f42c0..ec6259957d25 100644
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -827,6 +827,36 @@ static void amd_pstate_update_limits(unsigned int cpu)
>  	mutex_unlock(&amd_pstate_driver_lock);
>  }
>  
> +/**
> + * Get pstate transition delay time from ACPI tables that firmware set
> + * instead of using hardcode value directly.
> + */
> +static u32 amd_pstate_get_transition_delay_us(unsigned int cpu)
> +{
> +	u32 transition_delay_ns;
> +
> +	transition_delay_ns = cppc_get_transition_latency(cpu);
> +	if (transition_delay_ns == CPUFREQ_ETERNAL)
> +		return AMD_PSTATE_TRANSITION_DELAY;
> +
> +	return transition_delay_ns / NSEC_PER_USEC;
> +}
> +
> +/**
> + * Get pstate transition latency value from ACPI tables that firmware set
> + * instead of using hardcode value directly.
> + */
> +static u32 amd_pstate_get_transition_latency(unsigned int cpu)
> +{
> +	u32 transition_latency;
> +
> +	transition_latency = cppc_get_transition_latency(cpu);
> +	if (transition_latency  == CPUFREQ_ETERNAL)
> +		return AMD_PSTATE_TRANSITION_LATENCY;
> +
> +	return transition_latency;
> +}
> +
>  static int amd_pstate_cpu_init(struct cpufreq_policy *policy)
>  {
>  	int min_freq, max_freq, nominal_freq, lowest_nonlinear_freq, ret;
> @@ -867,8 +897,8 @@ static int amd_pstate_cpu_init(struct cpufreq_policy *policy)
>  		goto free_cpudata1;
>  	}
>  
> -	policy->cpuinfo.transition_latency = AMD_PSTATE_TRANSITION_LATENCY;
> -	policy->transition_delay_us = AMD_PSTATE_TRANSITION_DELAY;
> +	policy->cpuinfo.transition_latency = amd_pstate_get_transition_latency(policy->cpu);
> +	policy->transition_delay_us = amd_pstate_get_transition_delay_us(policy->cpu);
>  
>  	policy->min = min_freq;
>  	policy->max = max_freq;
> -- 
> 2.34.1
>