cpufreq: amd-pstate: Add guided mode control support via sysfs

amd_pstate driver's `status` sysfs entry helps to control the driver's
mode dynamically by user. After the addition of guided mode the
combinations of mode transitions have been increased (16 combinations).
Therefore optimise the amd_pstate_update_status function by implementing
a state transition table.

There are 4 states amd_pstate supports, namely: 'disable', 'passive',
'active', and 'guided'. The transition from any state to any other
state is possible after this change.

Sysfs interface:

To disable amd_pstate driver:
# echo disable > /sys/devices/system/cpu/amd_pstate/status

To enable passive mode:
# echo passive > /sys/devices/system/cpu/amd_pstate/status

To change mode to active:
# echo active > /sys/devices/system/cpu/amd_pstate/status

To change mode to guided:
# echo guided > /sys/devices/system/cpu/amd_pstate/status

Acked-by: Huang Rui <[e-mail]>
Reviewed-by: Mario Limonciello <[e-mail]>
Tested-by: Oleksandr Natalenko <[e-mail]>
Signed-off-by: Wyes Karny <[e-mail]>
Signed-off-by: Rafael J. Wysocki <[e-mail]>

drivers/cpufreq/amd-pstate.c

···
 	[EPP_INDEX_POWERSAVE] = AMD_CPPC_EPP_POWERSAVE,
  };
 
+typedef int (*cppc_mode_transition_fn)(int);
+
 static inline int get_mode_idx_from_str(const char *str, size_t size)
 {
 	int i;
···
 	return sysfs_emit(buf, "%s\n", energy_perf_strings[preference]);
 }
 
+static void amd_pstate_driver_cleanup(void)
+{
+	amd_pstate_enable(false);
+	cppc_state = AMD_PSTATE_DISABLE;
+	current_pstate_driver = NULL;
+}
+
+static int amd_pstate_register_driver(int mode)
+{
+	int ret;
+
+	if (mode == AMD_PSTATE_PASSIVE || mode == AMD_PSTATE_GUIDED)
+		current_pstate_driver = &amd_pstate_driver;
+	else if (mode == AMD_PSTATE_ACTIVE)
+		current_pstate_driver = &amd_pstate_epp_driver;
+	else
+		return -EINVAL;
+
+	cppc_state = mode;
+	ret = cpufreq_register_driver(current_pstate_driver);
+	if (ret) {
+		amd_pstate_driver_cleanup();
+		return ret;
+	}
+	return 0;
+}
+
+static int amd_pstate_unregister_driver(int dummy)
+{
+	cpufreq_unregister_driver(current_pstate_driver);
+	amd_pstate_driver_cleanup();
+	return 0;
+}
+
+static int amd_pstate_change_mode_without_dvr_change(int mode)
+{
+	int cpu = 0;
+
+	cppc_state = mode;
+
+	if (boot_cpu_has(X86_FEATURE_CPPC) || cppc_state == AMD_PSTATE_ACTIVE)
+		return 0;
+
+	for_each_present_cpu(cpu) {
+		cppc_set_auto_sel(cpu, (cppc_state == AMD_PSTATE_PASSIVE) ? 0 : 1);
+	}
+
+	return 0;
+}
+
+static int amd_pstate_change_driver_mode(int mode)
+{
+	int ret;
+
+	ret = amd_pstate_unregister_driver(0);
+	if (ret)
+		return ret;
+
+	ret = amd_pstate_register_driver(mode);
+	if (ret)
+		return ret;
+
+	return 0;
+}
+
+cppc_mode_transition_fn mode_state_machine[AMD_PSTATE_MAX][AMD_PSTATE_MAX] = {
+	[AMD_PSTATE_DISABLE]         = {
+		[AMD_PSTATE_DISABLE]     = NULL,
+		[AMD_PSTATE_PASSIVE]     = amd_pstate_register_driver,
+		[AMD_PSTATE_ACTIVE]      = amd_pstate_register_driver,
+		[AMD_PSTATE_GUIDED]      = amd_pstate_register_driver,
+	},
+	[AMD_PSTATE_PASSIVE]         = {
+		[AMD_PSTATE_DISABLE]     = amd_pstate_unregister_driver,
+		[AMD_PSTATE_PASSIVE]     = NULL,
+		[AMD_PSTATE_ACTIVE]      = amd_pstate_change_driver_mode,
+		[AMD_PSTATE_GUIDED]      = amd_pstate_change_mode_without_dvr_change,
+	},
+	[AMD_PSTATE_ACTIVE]          = {
+		[AMD_PSTATE_DISABLE]     = amd_pstate_unregister_driver,
+		[AMD_PSTATE_PASSIVE]     = amd_pstate_change_driver_mode,
+		[AMD_PSTATE_ACTIVE]      = NULL,
+		[AMD_PSTATE_GUIDED]      = amd_pstate_change_driver_mode,
+	},
+	[AMD_PSTATE_GUIDED]          = {
+		[AMD_PSTATE_DISABLE]     = amd_pstate_unregister_driver,
+		[AMD_PSTATE_PASSIVE]     = amd_pstate_change_mode_without_dvr_change,
+		[AMD_PSTATE_ACTIVE]      = amd_pstate_change_driver_mode,
+		[AMD_PSTATE_GUIDED]      = NULL,
+	},
+};
+
 static ssize_t amd_pstate_show_status(char *buf)
 {
 	if (!current_pstate_driver)
···
 	return sysfs_emit(buf, "%s\n", amd_pstate_mode_string[cppc_state]);
 }
 
-static void amd_pstate_driver_cleanup(void)
-{
-	current_pstate_driver = NULL;
-}
-
 static int amd_pstate_update_status(const char *buf, size_t size)
 {
-	int ret = 0;
 	int mode_idx;
 
-	if (size > 7 || size < 6)
+	if (size > strlen("passive") || size < strlen("active"))
 		return -EINVAL;
+
 	mode_idx = get_mode_idx_from_str(buf, size);
 
-	switch(mode_idx) {
-	case AMD_PSTATE_DISABLE:
-		if (!current_pstate_driver)
-			return -EINVAL;
-		if (cppc_state == AMD_PSTATE_ACTIVE)
-			return -EBUSY;
-		cpufreq_unregister_driver(current_pstate_driver);
-		amd_pstate_driver_cleanup();
-		break;
-	case AMD_PSTATE_PASSIVE:
-		if (current_pstate_driver) {
-			if (current_pstate_driver == &amd_pstate_driver)
-				return 0;
-			cpufreq_unregister_driver(current_pstate_driver);
-			cppc_state = AMD_PSTATE_PASSIVE;
-			current_pstate_driver = &amd_pstate_driver;
-		}
+	if (mode_idx < 0 || mode_idx >= AMD_PSTATE_MAX)
+		return -EINVAL;
 
-		ret = cpufreq_register_driver(current_pstate_driver);
-		break;
-	case AMD_PSTATE_ACTIVE:
-		if (current_pstate_driver) {
-			if (current_pstate_driver == &amd_pstate_epp_driver)
-				return 0;
-			cpufreq_unregister_driver(current_pstate_driver);
-			current_pstate_driver = &amd_pstate_epp_driver;
-			cppc_state = AMD_PSTATE_ACTIVE;
-		}
+	if (mode_state_machine[cppc_state][mode_idx])
+		return mode_state_machine[cppc_state][mode_idx](mode_idx);
 
-		ret = cpufreq_register_driver(current_pstate_driver);
-		break;
-	default:
-		ret = -EINVAL;
-		break;
-	}
-
-	return ret;
+	return 0;
 }
 
 static ssize_t show_status(struct kobject *kobj,