Re: [PATCH v2 01/10] cpufreq: amd-pstate: optimize the initial frequency values verification

[Dhananjay Ugwekar <Dhananjay.Ugwekar@amd.com>]

Hello Perry,

On 5/13/2024 7:37 AM, Perry Yuan wrote:
> To enhance the debugging capability of the driver loading failure for
> broken CPPC ACPI tables, it can optimize the expression by moving the
> verification of `min_freq`, `nominal_freq`, and other dependency values
> to the `amd_pstate_init_freq()` function where they are initialized.
> If any of these values are incorrect, the `amd-pstate` driver will not be registered.
> 
> By ensuring that these values are correct before they are used, it will facilitate
> the debugging process when encountering driver loading failures due to faulty CPPC
> ACPI tables from BIOS
> 
> Signed-off-by: Perry Yuan <perry.yuan@amd.com>
> ---
>  drivers/cpufreq/amd-pstate.c | 35 ++++++++++++++++++-----------------
>  1 file changed, 18 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> index 6a342b0c0140..614f6fac0764 100644
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -889,6 +889,24 @@ static int amd_pstate_init_freq(struct amd_cpudata *cpudata)
>  	WRITE_ONCE(cpudata->nominal_freq, nominal_freq);
>  	WRITE_ONCE(cpudata->max_freq, max_freq);
>  
> +	/**
> +	 * Below values need to be initialized correctly, otherwise driver will fail to load
> +	 * max_freq is calculated according to (nominal_freq * highest_perf)/nominal_perf
> +	 * lowest_nonlinear_freq is a value between [min_freq, nominal_freq]
> +	 * Check _CPC in ACPI table objects if any values are incorrect
> +	 */
> +	if (min_freq <= 0 || max_freq <= 0 || nominal_freq <= 0 || min_freq > max_freq) {
> +		pr_err("min_freq(%d) or max_freq(%d) or nominal_freq(%d) value is incorrect\n",
> +			min_freq, max_freq, nominal_freq);
> +		return -EINVAL;
> +	}
> +
> +	if (lowest_nonlinear_freq <= min_freq || lowest_nonlinear_freq > nominal_freq * 1000) {
> +		pr_err("lowest_nonlinear_freq(%d) value is out of range [min_freq(%d), nominal_freq(%d)]\n",
> +			lowest_nonlinear_freq, min_freq, nominal_freq * 1000);

A reminder, we should fix the below code section (due to only nominal freq being in MHz),

685 static int amd_pstate_set_boost(struct cpufreq_policy *policy, int state)                                                        
686 {                                                                                                                                
687         struct amd_cpudata *cpudata = policy->driver_data;                                                                       
688         int ret;                                                                                                                 
689                                                                                                                                  
690         if (!cpudata->boost_supported) {                                                                                         
691                 pr_err("Boost mode is not supported by this processor or SBIOS\n");                                              
692                 return -EINVAL;                                                                                                  
693         }                                                                                                                        
694                                                                                                                                  
695         if (state)                                                                                                               
696                 policy->cpuinfo.max_freq = cpudata->max_freq;                                                                    
697         else                                                                                                                     
698                 policy->cpuinfo.max_freq = cpudata->nominal_freq;      <--- mismatch in left and right hand side units  


To avoid below situation(from a Zen4 AMD EPYC system with boost disabled),

/sys/devices/system/cpu/cpu0/cpufreq# cat scaling_max_freq                                                             
2151                                                             	<--- MHz                                                                    
/sys/devices/system/cpu/cpu0/cpufreq# cat amd_pstate_max_freq                                                          
2287000									<--- KHz

Thanks,
Dhananjay


> +		return -EINVAL;
> +	}
> +
>  	return 0;
>  }
>  
> @@ -927,15 +945,6 @@ static int amd_pstate_cpu_init(struct cpufreq_policy *policy)
>  	max_freq = READ_ONCE(cpudata->max_freq);
>  	nominal_freq = READ_ONCE(cpudata->nominal_freq);
>  
> -	if (min_freq <= 0 || max_freq <= 0 ||
> -	    nominal_freq <= 0 || min_freq > max_freq) {
> -		dev_err(dev,
> -			"min_freq(%d) or max_freq(%d) or nominal_freq (%d) value is incorrect, check _CPC in ACPI tables\n",
> -			min_freq, max_freq, nominal_freq);
> -		ret = -EINVAL;
> -		goto free_cpudata1;
> -	}
> -
>  	policy->cpuinfo.transition_latency = amd_pstate_get_transition_latency(policy->cpu);
>  	policy->transition_delay_us = amd_pstate_get_transition_delay_us(policy->cpu);
>  
> @@ -1388,14 +1397,6 @@ static int amd_pstate_epp_cpu_init(struct cpufreq_policy *policy)
>  	min_freq = READ_ONCE(cpudata->min_freq);
>  	max_freq = READ_ONCE(cpudata->max_freq);
>  	nominal_freq = READ_ONCE(cpudata->nominal_freq);
> -	if (min_freq <= 0 || max_freq <= 0 ||
> -	    nominal_freq <= 0 || min_freq > max_freq) {
> -		dev_err(dev,
> -			"min_freq(%d) or max_freq(%d) or nominal_freq(%d) value is incorrect, check _CPC in ACPI tables\n",
> -			min_freq, max_freq, nominal_freq);
> -		ret = -EINVAL;
> -		goto free_cpudata1;
> -	}
>  
>  	policy->cpuinfo.min_freq = min_freq;
>  	policy->cpuinfo.max_freq = max_freq;