linux-kernel - Re: [PATCH 4/6] cpufreq:amd-pstate: get pstate transition delay and latency value from ACPI tables

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Date: Wed, 31 Jan 2024 15:49:14 -0600
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 4/6] cpufreq:amd-pstate: get pstate transition delay and
 latency value from ACPI tables

On 1/31/2024 02:50, 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
> 
> Signed-off-by: Perry Yuan <perry.yuan@....com>

One comment below.

Reviewed-by: Mario Limonciello <mario.limonciello@....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 db7b36afdce2..eea2e192d748 100644
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -683,6 +683,36 @@ static void amd_perf_ctl_reset(unsigned int cpu)
>   	wrmsrl_on_cpu(cpu, MSR_AMD_PERF_CTL, 0);
>   }
>   
> +/**
> + * 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);

space before the =

> +	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;
> @@ -725,8 +755,8 @@ 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;