cpufreq: intel_pstate: Request P-states control from SMM if needed

Currently, intel_pstate is unable to control P-states on my
IvyBridge-based Acer Aspire S5, because they are controlled by SMM
on that machine by default and it is necessary to request OS control
of P-states from it via the SMI Command register exposed in the ACPI
FADT.  intel_pstate doesn't do that now, but acpi-cpufreq and other
cpufreq drivers for x86 platforms do.

Address this problem by making intel_pstate use the ACPI-defined
mechanism as well.  However, intel_pstate is not modular and it
doesn't need the module refcount tricks played by
acpi_processor_notify_smm(), so export the core of this function
to it as acpi_processor_pstate_control() and make it call that.
[The changes in processor_perflib.c related to this should not
make any functional difference for the acpi_processor_notify_smm()
users].

To be safe, only call acpi_processor_notify_smm() from intel_pstate
if ACPI _PPC support is enabled in it.
Suggested-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>

drivers/acpi/processor_perflib.c

@@ -465,11 +465,33 @@ int acpi_processor_get_performance_info(struct acpi_processor *pr)
 	return result;
 }
 EXPORT_SYMBOL_GPL(acpi_processor_get_performance_info);
-int acpi_processor_notify_smm(struct module *calling_module)
+
+int acpi_processor_pstate_control(void)
 {
 	acpi_status status;
-	static int is_done = 0;
 
+	if (!acpi_gbl_FADT.smi_command || !acpi_gbl_FADT.pstate_control)
+		return 0;
+
+	ACPI_DEBUG_PRINT((ACPI_DB_INFO,
+			  "Writing pstate_control [0x%x] to smi_command [0x%x]\n",
+			  acpi_gbl_FADT.pstate_control, acpi_gbl_FADT.smi_command));
+
+	status = acpi_os_write_port(acpi_gbl_FADT.smi_command,
+				    (u32)acpi_gbl_FADT.pstate_control, 8);
+	if (ACPI_SUCCESS(status))
+		return 1;
+
+	ACPI_EXCEPTION((AE_INFO, status,
+			"Failed to write pstate_control [0x%x] to smi_command [0x%x]",
+			acpi_gbl_FADT.pstate_control, acpi_gbl_FADT.smi_command));
+	return -EIO;
+}
+
+int acpi_processor_notify_smm(struct module *calling_module)
+{
+	static int is_done = 0;
+	int result;
 
 	if (!(acpi_processor_ppc_status & PPC_REGISTERED))
 		return -EBUSY;
@@ -492,26 +514,15 @@ int acpi_processor_notify_smm(struct module *calling_module)
 
 	is_done = -EIO;
 
-	/* Can't write pstate_control to smi_command if either value is zero */
-	if ((!acpi_gbl_FADT.smi_command) || (!acpi_gbl_FADT.pstate_control)) {
+	result = acpi_processor_pstate_control();
+	if (!result) {
 		ACPI_DEBUG_PRINT((ACPI_DB_INFO, "No SMI port or pstate_control\n"));
 		module_put(calling_module);
 		return 0;
 	}
-
-	ACPI_DEBUG_PRINT((ACPI_DB_INFO,
-			  "Writing pstate_control [0x%x] to smi_command [0x%x]\n",
-			  acpi_gbl_FADT.pstate_control, acpi_gbl_FADT.smi_command));
-
-	status = acpi_os_write_port(acpi_gbl_FADT.smi_command,
-				    (u32) acpi_gbl_FADT.pstate_control, 8);
-	if (ACPI_FAILURE(status)) {
-		ACPI_EXCEPTION((AE_INFO, status,
-				"Failed to write pstate_control [0x%x] to "
-				"smi_command [0x%x]", acpi_gbl_FADT.pstate_control,
-				acpi_gbl_FADT.smi_command));
+	if (result < 0) {
 		module_put(calling_module);
-		return status;
+		return result;
 	}
 
 	/* Success. If there's no _PPC, we need to fear nothing, so

drivers/cpufreq/intel_pstate.c

@@ -1909,9 +1909,20 @@ static bool __init intel_pstate_platform_pwr_mgmt_exists(void)
 
 	return false;
 }
+
+static void intel_pstate_request_control_from_smm(void)
+{
+	/*
+	 * It may be unsafe to request P-states control from SMM if _PPC support
+	 * has not been enabled.
+	 */
+	if (acpi_ppc)
+		acpi_processor_pstate_control();
+}
 #else /* CONFIG_ACPI not enabled */
 static inline bool intel_pstate_platform_pwr_mgmt_exists(void) { return false; }
 static inline bool intel_pstate_has_acpi_ppc(void) { return false; }
+static inline void intel_pstate_request_control_from_smm(void) {}
 #endif /* CONFIG_ACPI */
 
 static const struct x86_cpu_id hwp_support_ids[] __initconst = {
@@ -1963,6 +1974,8 @@ static int __init intel_pstate_init(void)
 	if (!hwp_active && hwp_only)
 		goto out;
 
+	intel_pstate_request_control_from_smm();
+
 	rc = cpufreq_register_driver(&intel_pstate_driver);
 	if (rc)
 		goto out;

include/acpi/processor.h

@@ -249,6 +249,7 @@ extern int acpi_processor_register_performance(struct acpi_processor_performance
 					       *performance, unsigned int cpu);
 extern void acpi_processor_unregister_performance(unsigned int cpu);
 
+int acpi_processor_pstate_control(void);
 /* note: this locks both the calling module and the processor module
          if a _PPC object exists, rmmod is disallowed then */
 int acpi_processor_notify_smm(struct module *calling_module);