ACPI: processor: Export function to claim _CST control

The intel_idle driver will be modified to use ACPI _CST subsequently
and it will need to notify the platform firmware of that if
acpi_gbl_FADT.cst_control is set, so add a routine for this purpose,
acpi_processor_claim_cst_control(), to acpi_processor.c (so that it
is always present which is required by intel_idle) and export it
to allow the ACPI processor driver (which is modular) to call it.

No intentional functional impact.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/acpi_processor.c

@@ -705,3 +705,28 @@ void __init acpi_processor_init(void)
 	acpi_scan_add_handler_with_hotplug(&processor_handler, "processor");
 	acpi_scan_add_handler(&processor_container_handler);
 }
+
+#ifdef CONFIG_ACPI_PROCESSOR_CSTATE
+/**
+ * acpi_processor_claim_cst_control - Request _CST control from the platform.
+ */
+bool acpi_processor_claim_cst_control(void)
+{
+	static bool cst_control_claimed;
+	acpi_status status;
+
+	if (!acpi_gbl_FADT.cst_control || cst_control_claimed)
+		return true;
+
+	status = acpi_os_write_port(acpi_gbl_FADT.smi_command,
+				    acpi_gbl_FADT.cst_control, 8);
+	if (ACPI_FAILURE(status)) {
+		pr_warn("ACPI: Failed to claim processor _CST control\n");
+		return false;
+	}
+
+	cst_control_claimed = true;
+	return true;
+}
+EXPORT_SYMBOL_GPL(acpi_processor_claim_cst_control);
+#endif /* CONFIG_ACPI_PROCESSOR_CSTATE */

drivers/acpi/processor_idle.c

@@ -909,7 +909,6 @@ static int acpi_processor_setup_cstates(struct acpi_processor *pr)
 
 static inline void acpi_processor_cstate_first_run_checks(void)
 {
-	acpi_status status;
 	static int first_run;
 
 	if (first_run)
@@ -921,13 +920,10 @@ static inline void acpi_processor_cstate_first_run_checks(void)
 			  max_cstate);
 	first_run++;
 
-	if (acpi_gbl_FADT.cst_control && !nocst) {
-		status = acpi_os_write_port(acpi_gbl_FADT.smi_command,
-					    acpi_gbl_FADT.cst_control, 8);
-		if (ACPI_FAILURE(status))
-			ACPI_EXCEPTION((AE_INFO, status,
-					"Notifying BIOS of _CST ability failed"));
-	}
+	if (nocst)
+		return;
+
+	acpi_processor_claim_cst_control();
 }
 #else
 

include/linux/acpi.h

@@ -279,6 +279,12 @@ static inline bool invalid_phys_cpuid(phys_cpuid_t phys_id)
 
 /* Validate the processor object's proc_id */
 bool acpi_duplicate_processor_id(int proc_id);
+/* Processor _CTS control */
+#ifdef CONFIG_ACPI_PROCESSOR_CSTATE
+bool acpi_processor_claim_cst_control(void);
+#else
+static inline bool acpi_processor_claim_cst_control(void) { return false; }
+#endif
 
 #ifdef CONFIG_ACPI_HOTPLUG_CPU
 /* Arch dependent functions for cpu hotplug support */