Re: [PATCH] ACPI: CPPC: Don't gate FFH EPP writes on flexible address space _OSC

On 8/31/26 00:40, Mario Limonciello wrote:
> cppc_set_epp_perf() requires osc_cpc_flexible_adr_space_confirmed before
> writing the EPP and autonomous-selection registers, even when they live
> in FFH.  FFH access is a direct rdmsr/wrmsr and does not depend on that
> _OSC bit, which only governs CPPC controls in SystemMemory/SystemIO.
> 
> As a result amd-pstate active mode fails to initialize on platforms whose
> firmware does not ack CPPC in _OSC but whose EPP register is a working FFH
> MSR.  On an HP 255 G8 (Ryzen 5 5500U) reads succeed via the _CPC parse
> path's cpc_supported_by_cpu() fallback, but the EPP write is rejected:
> 
>      amd_pstate: failed to set energy perf value (-524)
>      amd_pstate: failed to register with return -19
> 
> Gate only SystemMemory on osc_cpc_flexible_adr_space_confirmed and allow
> FFH unconditionally, matching the _CPC parse path and cpc_ffh_supported().
> 
> Fixes: aaf21ac93909 ("ACPI: CPPC: Add support for setting EPP register in FFH")
> Reported-by: Giusy <[email protected]>
> Closes: https://lore.kernel.org/linux-pm/[email protected]/
> Assisted-by: Claude:claude-opus-4-8
> Signed-off-by: Mario Limonciello <[email protected]>
> ---
>   drivers/acpi/cppc_acpi.c | 15 +++++++++++----
>   1 file changed, 11 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
> index fef54fcd00b78..6b590842b5668 100644
> --- a/drivers/acpi/cppc_acpi.c
> +++ b/drivers/acpi/cppc_acpi.c
> @@ -1766,10 +1766,18 @@ int cppc_set_epp_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls, bool enable)
>   	auto_sel_reg = &cpc_desc->cpc_regs[AUTO_SEL_ENABLE];
>   	epp_set_reg = &cpc_desc->cpc_regs[ENERGY_PERF];
>   
> +	/*
> +	 * The flexible address space _OSC ack is only needed for
> +	 * SystemMemory/SystemIO; FFH is accessed directly and always available.
> +	 */
>   	epp_ffh_sysmem = CPC_SUPPORTED(epp_set_reg) &&
> -		(CPC_IN_FFH(epp_set_reg) || CPC_IN_SYSTEM_MEMORY(epp_set_reg));
> +		(CPC_IN_FFH(epp_set_reg) ||
> +		 (CPC_IN_SYSTEM_MEMORY(epp_set_reg) &&
> +		  osc_cpc_flexible_adr_space_confirmed));
>   	autosel_ffh_sysmem = CPC_SUPPORTED(auto_sel_reg) &&
> -		(CPC_IN_FFH(auto_sel_reg) || CPC_IN_SYSTEM_MEMORY(auto_sel_reg));
> +		(CPC_IN_FFH(auto_sel_reg) ||
> +		 (CPC_IN_SYSTEM_MEMORY(auto_sel_reg) &&
> +		  osc_cpc_flexible_adr_space_confirmed));
>   
>   	if (CPC_IN_PCC(epp_set_reg) || CPC_IN_PCC(auto_sel_reg)) {
>   		if (pcc_ss_id < 0) {
> @@ -1795,8 +1803,7 @@ int cppc_set_epp_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls, bool enable)
>   		/* after writing CPC, transfer the ownership of PCC to platform */
>   		ret = send_pcc_cmd(pcc_ss_id, CMD_WRITE);
>   		up_write(&pcc_ss_data->pcc_lock);
> -	} else if (osc_cpc_flexible_adr_space_confirmed &&
> -		   (epp_ffh_sysmem || autosel_ffh_sysmem)) {
> +	} else if (epp_ffh_sysmem || autosel_ffh_sysmem) {
>   		if (autosel_ffh_sysmem) {
>   			ret = cpc_write(cpu, auto_sel_reg, enable);
>   			if (ret)

This patch can be dropped as 
https://lore.kernel.org/linux-acpi/[email protected]/#t 
will fix it.

FFH writes being gated on the _OSC ack — no longer exist due to the 
refactoring.