RE: [PATCH] ACPI: CPPC: Don't require _OSC if X86_FEATURE_CPPC is supported

["Yuan, Perry" <Perry.Yuan@amd.com>]

[AMD Official Use Only - General]

Hi Rafael:

> -----Original Message-----
> From: Limonciello, Mario <Mario.Limonciello@amd.com>
> Sent: Tuesday, June 28, 2022 12:59 AM
> To: Limonciello, Mario <Mario.Limonciello@amd.com>; Rafael J. Wysocki
> <rafael@kernel.org>; Len Brown <lenb@kernel.org>; Pierre Gondois
> <pierre.gondois@arm.com>; Sudeep Holla <sudeep.holla@arm.com>
> Cc: Yuan, Perry <Perry.Yuan@amd.com>; linux-acpi@vger.kernel.org; linux-
> kernel@vger.kernel.org
> Subject: [PATCH] ACPI: CPPC: Don't require _OSC if X86_FEATURE_CPPC is
> supported
> 
> commit 72f2ecb7ece7 ("ACPI: bus: Set CPPC _OSC bits for all and when
> CPPC_LIB is supported") added support for claiming to support CPPC in _OSC
> on non-Intel platforms.
> 
> This unfortunately caused a regression on a vartiety of AMD platforms in the
> field because a number of AMD platforms don't set the `_OSC` bit 5 or 6 to
> indicate CPPC or CPPC v2 support.
> 
> As these AMD platforms already claim CPPC support via
> `X86_FEATURE_CPPC`, use this enable this feature rather than requiring the
> `_OSC`.
> 
> Fixes: 72f2ecb7ece7 ("Set CPPC _OSC bits for all and when CPPC_LIB is
> supported")
> Reported-by: Perry Yuan <perry.yuan@amd.com>
> Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
> ---
>  drivers/acpi/cppc_acpi.c | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c index
> 903528f7e187..5463e6309b9a 100644
> --- a/drivers/acpi/cppc_acpi.c
> +++ b/drivers/acpi/cppc_acpi.c
> @@ -629,6 +629,15 @@ static bool is_cppc_supported(int revision, int
> num_ent)
>  		return false;
>  	}
> 
> +	if (osc_sb_cppc_not_supported) {
> +		pr_debug("Firmware missing _OSC support\n"); #ifdef
> CONFIG_X86
> +		return boot_cpu_has(X86_FEATURE_CPPC); #else
> +		return false;
> +#endif
> +	}
> +
>  	return true;
>  }
> 

I align with Mario to use his patch to fix the amd pstate driver loading failure issue.
AMD CPUID include the cppc flag to mark the CPPC valid  if the _OSC dose not have the CPPC support info added.

Tested-by: Perry Yuan <perry.yuan@amd.com>


> @@ -684,9 +693,6 @@ int acpi_cppc_processor_probe(struct
> acpi_processor *pr)
>  	acpi_status status;
>  	int ret = -ENODATA;
> 
> -	if (osc_sb_cppc_not_supported)
> -		return -ENODEV;
> -
>  	/* Parse the ACPI _CPC table for this CPU. */
>  	status = acpi_evaluate_object_typed(handle, "_CPC", NULL, &output,
>  			ACPI_TYPE_PACKAGE);
> --
> 2.34.1