Re: [PATCH 1/2] ACPI: CPPC: Add support for CPPC v4

[Mario Limonciello <superm1@kernel.org>]

On 4/27/26 00:18, Sumit Gupta wrote:
> CPPC v4 (ACPI 6.6, Section 8.4.6) adds two optional entries to the
> _CPC package:
> 
> 1. OSPM Nominal Performance (8.4.6.1.2.6): A write-only register that
>     lets OSPM inform the platform what it considers nominal performance.
>     The platform classifies performance above this level as boost and
>     below as throttle for its power/thermal decisions.
> 
> 2. Resource Priority (8.4.6.1.2.7): A Package of Resource Priority
>     Register Descriptor sub-packages that allow OSPM to set relative
>     priority among processors for shared resources (boost, throttle,
>     L2/L3 cache, memory bandwidth). Parsing the full structure is not
>     yet supported; such entries are marked as unsupported.
> 
> Add v4 _CPC table parsing (25 entries) and update REG_OPTIONAL to
> mark the two new registers as optional.
> 
> Signed-off-by: Sumit Gupta <sumitg@nvidia.com>
Reviewed-by: Mario Limonciello (AMD) <superm1@kernel.org>
> ---
>   drivers/acpi/cppc_acpi.c | 24 ++++++++++++++++++------
>   include/acpi/cppc_acpi.h |  8 ++++++--
>   2 files changed, 24 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
> index 2e91c5a97761..a1c91ce20cc8 100644
> --- a/drivers/acpi/cppc_acpi.c
> +++ b/drivers/acpi/cppc_acpi.c
> @@ -134,7 +134,7 @@ static DEFINE_PER_CPU(struct cpc_desc *, cpc_desc_ptr);
>    * cpc_regs[] with the corresponding index. 0 means mandatory and 1
>    * means optional.
>    */
> -#define REG_OPTIONAL (0x1FC7D0)
> +#define REG_OPTIONAL (0x7FC7D0)
>   
>   /*
>    * Use the index of the register in per-cpu cpc_regs[] to check if
> @@ -751,18 +751,19 @@ int acpi_cppc_processor_probe(struct acpi_processor *pr)
>   	/*
>   	 * Disregard _CPC if the number of entries in the return package is not
>   	 * as expected, but support future revisions being proper supersets of
> -	 * the v3 and only causing more entries to be returned by _CPC.
> +	 * the v4 and only causing more entries to be returned by _CPC.
>   	 */
>   	if ((cpc_rev == CPPC_V2_REV && num_ent != CPPC_V2_NUM_ENT) ||
>   	    (cpc_rev == CPPC_V3_REV && num_ent != CPPC_V3_NUM_ENT) ||
> -	    (cpc_rev > CPPC_V3_REV && num_ent <= CPPC_V3_NUM_ENT)) {
> +	    (cpc_rev == CPPC_V4_REV && num_ent != CPPC_V4_NUM_ENT) ||
> +	    (cpc_rev > CPPC_V4_REV && num_ent <= CPPC_V4_NUM_ENT)) {
>   		pr_debug("Unexpected number of _CPC return package entries (%d) for CPU:%d\n",
>   			 num_ent, pr->id);
>   		goto out_free;
>   	}
> -	if (cpc_rev > CPPC_V3_REV) {
> -		num_ent = CPPC_V3_NUM_ENT;
> -		cpc_rev = CPPC_V3_REV;
> +	if (cpc_rev > CPPC_V4_REV) {
> +		num_ent = CPPC_V4_NUM_ENT;
> +		cpc_rev = CPPC_V4_REV;
>   	}
>   
>   	cpc_ptr->num_entries = num_ent;
> @@ -845,6 +846,17 @@ int acpi_cppc_processor_probe(struct acpi_processor *pr)
>   
>   			cpc_ptr->cpc_regs[i-2].type = ACPI_TYPE_BUFFER;
>   			memcpy(&cpc_ptr->cpc_regs[i-2].cpc_entry.reg, gas_t, sizeof(*gas_t));
> +		} else if (cpc_obj->type == ACPI_TYPE_PACKAGE) {
> +			/*
> +			 * ACPI 6.6, s8.4.6.1.2.7 defines Resource Priority
> +			 * as a Package of Resource Priority Register Descriptor
> +			 * sub-packages.  Parsing the full structure is not yet
> +			 * supported; mark the register as unsupported for now.
> +			 */
> +			pr_debug("CPU:%d entry %d: package type not supported\n",
> +				 pr->id, i);
> +			cpc_ptr->cpc_regs[i-2].type = ACPI_TYPE_INTEGER;
> +			cpc_ptr->cpc_regs[i-2].cpc_entry.int_value = 0;
>   		} else {
>   			pr_debug("Invalid entry type (%d) in _CPC for CPU:%d\n",
>   				 i, pr->id);
> diff --git a/include/acpi/cppc_acpi.h b/include/acpi/cppc_acpi.h
> index d1f02ceec4f9..8693890a7275 100644
> --- a/include/acpi/cppc_acpi.h
> +++ b/include/acpi/cppc_acpi.h
> @@ -17,16 +17,18 @@
>   #include <acpi/pcc.h>
>   #include <acpi/processor.h>
>   
> -/* CPPCv2 and CPPCv3 support */
> +/* CPPCv2, CPPCv3 and CPPCv4 support */
>   #define CPPC_V2_REV	2
>   #define CPPC_V3_REV	3
> +#define CPPC_V4_REV	4
>   #define CPPC_V2_NUM_ENT	21
>   #define CPPC_V3_NUM_ENT	23
> +#define CPPC_V4_NUM_ENT	25
>   
>   #define PCC_CMD_COMPLETE_MASK	(1 << 0)
>   #define PCC_ERROR_MASK		(1 << 2)
>   
> -#define MAX_CPC_REG_ENT 21
> +#define MAX_CPC_REG_ENT 23
>   
>   /* CPPC specific PCC commands. */
>   #define	CMD_READ 0
> @@ -109,6 +111,8 @@ enum cppc_regs {
>   	REFERENCE_PERF,
>   	LOWEST_FREQ,
>   	NOMINAL_FREQ,
> +	OSPM_NOMINAL_PERF,
> +	RESOURCE_PRIORITY,
>   };
>   
>   /*