ACPI: CPPC: Add support for setting EPP register in FFH

Some Asus AMD systems are reported to not be able to change EPP values
because the BIOS doesn't advertise support for the CPPC MSR and the PCC
region is not configured.

However the ACPI 6.2 specification allows CPC registers to be declared
in FFH:
```
Starting with ACPI Specification 6.2, all _CPC registers can be in
PCC, System Memory, System IO, or Functional Fixed Hardware address
spaces. OSPM support for this more flexible register space scheme
is indicated by the “Flexible Address Space for CPPC Registers” _OSC
bit.
```

If this _OSC has been set allow using FFH to configure EPP.

Reported-by: [email protected]
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=218686
Suggested-by: [email protected]
Tested-by: [email protected]
Tested-by: [email protected]
Signed-off-by: Mario Limonciello <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Rafael J. Wysocki <[email protected]>

Author: superm1

drivers/acpi/cppc_acpi.c

@@ -103,6 +103,11 @@ static DEFINE_PER_CPU(struct cpc_desc *, cpc_desc_ptr);
 				(cpc)->cpc_entry.reg.space_id ==	\
 				ACPI_ADR_SPACE_PLATFORM_COMM)
 
+/* Check if a CPC register is in FFH */
+#define CPC_IN_FFH(cpc) ((cpc)->type == ACPI_TYPE_BUFFER &&		\
+				(cpc)->cpc_entry.reg.space_id ==	\
+				ACPI_ADR_SPACE_FIXED_HARDWARE)
+
 /* Check if a CPC register is in SystemMemory */
 #define CPC_IN_SYSTEM_MEMORY(cpc) ((cpc)->type == ACPI_TYPE_BUFFER &&	\
 				(cpc)->cpc_entry.reg.space_id ==	\
@@ -1521,9 +1526,12 @@ 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 &&
+		   CPC_SUPPORTED(epp_set_reg) && CPC_IN_FFH(epp_set_reg)) {
+		ret = cpc_write(cpu, epp_set_reg, perf_ctrls->energy_perf);
 	} else {
 		ret = -ENOTSUPP;
-		pr_debug("_CPC in PCC is not supported\n");
+		pr_debug("_CPC in PCC and _CPC in FFH are not supported\n");
 	}
 
 	return ret;