Re: [PATCH v3 05/15] xen/x86: introduce "cpufreq=amd-cppc" xen cmdline

[Jan Beulich <jbeulich@xxxxxxxx>]

On 06.03.2025 09:39, Penny Zheng wrote:
> @@ -514,5 +515,14 @@ acpi_cpufreq_driver = {
>  
>  int __init acpi_cpufreq_register(void)
>  {
> -    return cpufreq_register_driver(&acpi_cpufreq_driver);
> +    int ret;
> +
> +    ret = cpufreq_register_driver(&acpi_cpufreq_driver);
> +    if ( ret )
> +        return ret;
> +
> +    if ( IS_ENABLED(CONFIG_AMD) )
> +        xen_processor_pmbits &= ~XEN_PROCESSOR_PM_CPPC;

What's the purpose of the if() here?

> @@ -157,7 +161,35 @@ static int __init cf_check cpufreq_driver_init(void)
>  
>          case X86_VENDOR_AMD:
>          case X86_VENDOR_HYGON:
> -            ret = IS_ENABLED(CONFIG_AMD) ? powernow_register_driver() : 
> -ENODEV;
> +            if ( !IS_ENABLED(CONFIG_AMD) )
> +            {
> +                ret = -ENODEV;
> +                break;
> +            }
> +            ret = -ENOENT;
> +
> +            for ( unsigned int i = 0; i < cpufreq_xen_cnt; i++ )
> +            {
> +                switch ( cpufreq_xen_opts[i] )
> +                {
> +                case CPUFREQ_xen:
> +                    ret = powernow_register_driver();
> +                    break;
> +                case CPUFREQ_amd_cppc:
> +                    ret = amd_cppc_register_driver();
> +                    break;
> +                case CPUFREQ_none:
> +                    ret = 0;
> +                    break;
> +                default:
> +                    printk(XENLOG_WARNING
> +                           "Unsupported cpufreq driver for vendor AMD\n");

What about Hygon?

> --- a/xen/include/acpi/cpufreq/cpufreq.h
> +++ b/xen/include/acpi/cpufreq/cpufreq.h
> @@ -28,6 +28,7 @@ enum cpufreq_xen_opt {
>      CPUFREQ_none,
>      CPUFREQ_xen,
>      CPUFREQ_hwp,
> +    CPUFREQ_amd_cppc,
>  };
>  extern enum cpufreq_xen_opt cpufreq_xen_opts[2];

I'm pretty sure I pointed out before that this array needs to grow, now that
you add a 3rd kind of handling.

Jan