Re: [PATCH v8 1/8] xen/cpufreq: introduce new sub-hypercall to propagate CPPC data

[Jan Beulich <jbeulich@xxxxxxxx>]

On 28.08.2025 12:02, Penny Zheng wrote:
> In order to provide backward compatibility with existing governors
> that represent performance as frequency, like ondemand, the _CPC
> table can optionally provide processor frequency range values, Lowest
> frequency and Nominal frequency, to let OS use Lowest Frequency/
> Performance and Nominal Frequency/Performance as anchor points to
> create linear mapping of CPPC performance to CPU frequency.
> 
> As Xen is uncapable of parsing the ACPI dynamic table, we'd like to
> introduce a new sub-hypercall "XEN_PM_CPPC" to propagate required CPPC
> data from dom0 kernel to Xen.
> In the according handler set_cppc_pminfo(), we do _CPC and _PSD
> sanitization check, as both _PSD and _CPC info are necessary for correctly
> initializing cpufreq cores in CPPC mode.
> Users shall be warned that if we failed at this point,
> no fallback scheme, like legacy P-state could be switched to.
> 
> A new flag "XEN_CPPC_INIT" is also introduced for cpufreq core initialised in
> CPPC mode. Then all .init flag checking shall be updated to
> consider "XEN_CPPC_INIT" too.
> 
> We want to bypass construction of px statistic info in 
> cpufreq_statistic_init()
> for CPPC mode, while not bypassing cpufreq_statistic_lock initialization for a
> good reason. The same check is unnecessary for cpufreq_statistic_exit(),
> since it has already been covered by px statistic variable
> "cpufreq_statistic_data" check
> 
> Signed-off-by: Penny Zheng <Penny.Zheng@xxxxxxx>

Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
with two cosmetic issues taken care of (which I'll do while committing):

> @@ -693,6 +699,120 @@ int acpi_set_pdc_bits(unsigned int acpi_id, 
> XEN_GUEST_HANDLE(uint32) pdc)
>      return ret;
>  }
>  
> +static void print_CPPC(const struct xen_processor_cppc *cppc_data)
> +{
> +    printk("\t_CPC: highest_perf=%u, lowest_perf=%u, "
> +           "nominal_perf=%u, lowest_nonlinear_perf=%u, "
> +           "nominal_mhz=%uMHz, lowest_mhz=%uMHz\n",
> +           cppc_data->cpc.highest_perf, cppc_data->cpc.lowest_perf,
> +           cppc_data->cpc.nominal_perf, cppc_data->cpc.lowest_nonlinear_perf,
> +           cppc_data->cpc.nominal_mhz, cppc_data->cpc.lowest_mhz);
> +}
> +
> +int set_cppc_pminfo(unsigned int acpi_id,
> +                    const struct xen_processor_cppc *cppc_data)
> +{
> +    int ret = 0, cpuid;
> +    struct processor_pminfo *pm_info;
> +
> +    cpuid = get_cpu_id(acpi_id);
> +    if ( cpuid < 0 )
> +    {
> +        ret = -EINVAL;
> +        goto out;
> +    }
> +
> +    if ( cppc_data->pad[0] || cppc_data->pad[1] || cppc_data->pad[2] )
> +    {
> +        ret = -EINVAL;
> +        goto out;
> +    }
> +
> +    if ( cpufreq_verbose )
> +        printk("Set CPU%d (ACPI ID %u) CPPC state info:\n",
> +               cpuid, acpi_id);
> +
> +    pm_info = processor_pminfo[cpuid];
> +    if ( !pm_info )
> +    {
> +        pm_info = xvzalloc(struct processor_pminfo);
> +        if ( !pm_info )
> +        {
> +            ret = -ENOMEM;
> +            goto out;
> +        }
> +        processor_pminfo[cpuid] = pm_info;
> +    }
> +    pm_info->acpi_id = acpi_id;
> +    pm_info->id = cpuid;
> +    pm_info->cppc_data = *cppc_data;
> +
> +    if ( (cppc_data->flags & XEN_CPPC_PSD) &&
> +          !check_psd_pminfo(cppc_data->shared_type) )

Nit: Indentation is off by 1.

> +    {
> +            ret = -EINVAL;
> +            goto out;

Indentation is still wrong here.

Jan