Merge branches 'pm-cpufreq' and 'pm-cpuidle'

Merge cpufreq and cpuidle updates for 6.5-rc1:

 - Prevent cpufreq drivers that provide the ->adjust_perf() callback
   without a ->fast_switch() one which is used as a fallback from the
   former in some cases (Wyes Karny).

 - Fix some issues related to the AMD P-state cpufreq driver (Mario
   Limonciello, Wyes Karny).

 - Fix the energy_performance_preference attribute handling in the
   intel_pstate driver in passive mode (Tero Kristo).

 - Clean up the intel_idle driver, make it work with VM guests that
   cannot use the MWAIT instruction and address the case in which the
   host may enter a deep idle state when the guest is idle (Arjan van
   de Ven).

* pm-cpufreq:
  cpufreq: intel_pstate: Fix energy_performance_preference for passive
  cpufreq: amd-pstate: Add a kernel config option to set default mode
  cpufreq: amd-pstate: Set a fallback policy based on preferred_profile
  ACPI: CPPC: Add definition for undefined FADT preferred PM profile value
  cpufreq: amd-pstate: Set default governor to schedutil
  cpufreq: amd-pstate: Make amd-pstate EPP driver name hyphenated
  cpufreq: amd-pstate: Write CPPC enable bit per-socket
  cpufreq: Fail driver register if it has adjust_perf without fast_switch

* pm-cpuidle:
  intel_idle: Add a "Long HLT" C1 state for the VM guest mode
  intel_idle: Add support for using intel_idle in a VM guest using just hlt
  intel_idle: clean up the (new) state_update_enter_method function
  intel_idle: refactor state->enter manipulation into its own function

drivers/cpufreq/Kconfig

@@ -38,7 +38,7 @@ choice
 	prompt "Default CPUFreq governor"
 	default CPU_FREQ_DEFAULT_GOV_USERSPACE if ARM_SA1110_CPUFREQ
 	default CPU_FREQ_DEFAULT_GOV_SCHEDUTIL if ARM64 || ARM
-	default CPU_FREQ_DEFAULT_GOV_SCHEDUTIL if X86_INTEL_PSTATE && SMP
+	default CPU_FREQ_DEFAULT_GOV_SCHEDUTIL if (X86_INTEL_PSTATE || X86_AMD_PSTATE) && SMP
 	default CPU_FREQ_DEFAULT_GOV_PERFORMANCE
 	help
 	  This option sets which CPUFreq governor shall be loaded at

drivers/cpufreq/Kconfig.x86

@@ -51,6 +51,23 @@ config X86_AMD_PSTATE
 
 	  If in doubt, say N.
 
+config X86_AMD_PSTATE_DEFAULT_MODE
+	int "AMD Processor P-State default mode"
+	depends on X86_AMD_PSTATE
+	default 3 if X86_AMD_PSTATE
+	range 1 4
+	help
+	  Select the default mode the amd-pstate driver will use on
+	  supported hardware.
+	  The value set has the following meanings:
+		1 -> Disabled
+		2 -> Passive
+		3 -> Active (EPP)
+		4 -> Guided
+
+	  For details, take a look at:
+	  <file:Documentation/admin-guide/pm/amd-pstate.rst>.
+
 config X86_AMD_PSTATE_UT
 	tristate "selftest for AMD Processor P-State driver"
 	depends on X86 && ACPI_PROCESSOR

drivers/cpufreq/amd-pstate.c

@@ -62,7 +62,8 @@
 static struct cpufreq_driver *current_pstate_driver;
 static struct cpufreq_driver amd_pstate_driver;
 static struct cpufreq_driver amd_pstate_epp_driver;
-static int cppc_state = AMD_PSTATE_DISABLE;
+static int cppc_state = AMD_PSTATE_UNDEFINED;
+static bool cppc_enabled;
 
 /*
  * AMD Energy Preference Performance (EPP)
@@ -228,7 +229,28 @@ static int amd_pstate_set_energy_pref_index(struct amd_cpudata *cpudata,
 
 static inline int pstate_enable(bool enable)
 {
-	return wrmsrl_safe(MSR_AMD_CPPC_ENABLE, enable);
+	int ret, cpu;
+	unsigned long logical_proc_id_mask = 0;
+
+	if (enable == cppc_enabled)
+		return 0;
+
+	for_each_present_cpu(cpu) {
+		unsigned long logical_id = topology_logical_die_id(cpu);
+
+		if (test_bit(logical_id, &logical_proc_id_mask))
+			continue;
+
+		set_bit(logical_id, &logical_proc_id_mask);
+
+		ret = wrmsrl_safe_on_cpu(cpu, MSR_AMD_CPPC_ENABLE,
+				enable);
+		if (ret)
+			return ret;
+	}
+
+	cppc_enabled = enable;
+	return 0;
 }
 
 static int cppc_enable(bool enable)
@@ -236,6 +258,9 @@ static int cppc_enable(bool enable)
 	int cpu, ret = 0;
 	struct cppc_perf_ctrls perf_ctrls;
 
+	if (enable == cppc_enabled)
+		return 0;
+
 	for_each_present_cpu(cpu) {
 		ret = cppc_set_enable(cpu, enable);
 		if (ret)
@@ -251,6 +276,7 @@ static int cppc_enable(bool enable)
 		}
 	}
 
+	cppc_enabled = enable;
 	return ret;
 }
 
@@ -1045,6 +1071,26 @@ static const struct attribute_group amd_pstate_global_attr_group = {
 	.attrs = pstate_global_attributes,
 };
 
+static bool amd_pstate_acpi_pm_profile_server(void)
+{
+	switch (acpi_gbl_FADT.preferred_profile) {
+	case PM_ENTERPRISE_SERVER:
+	case PM_SOHO_SERVER:
+	case PM_PERFORMANCE_SERVER:
+		return true;
+	}
+	return false;
+}
+
+static bool amd_pstate_acpi_pm_profile_undefined(void)
+{
+	if (acpi_gbl_FADT.preferred_profile == PM_UNSPECIFIED)
+		return true;
+	if (acpi_gbl_FADT.preferred_profile >= NR_PM_PROFILES)
+		return true;
+	return false;
+}
+
 static int amd_pstate_epp_cpu_init(struct cpufreq_policy *policy)
 {
 	int min_freq, max_freq, nominal_freq, lowest_nonlinear_freq, ret;
@@ -1102,10 +1148,14 @@ static int amd_pstate_epp_cpu_init(struct cpufreq_policy *policy)
 	policy->max = policy->cpuinfo.max_freq;
 
 	/*
-	 * Set the policy to powersave to provide a valid fallback value in case
+	 * Set the policy to provide a valid fallback value in case
 	 * the default cpufreq governor is neither powersave nor performance.
 	 */
-	policy->policy = CPUFREQ_POLICY_POWERSAVE;
+	if (amd_pstate_acpi_pm_profile_server() ||
+	    amd_pstate_acpi_pm_profile_undefined())
+		policy->policy = CPUFREQ_POLICY_PERFORMANCE;
+	else
+		policy->policy = CPUFREQ_POLICY_POWERSAVE;
 
 	if (boot_cpu_has(X86_FEATURE_CPPC)) {
 		ret = rdmsrl_on_cpu(cpudata->cpu, MSR_AMD_CPPC_REQ, &value);
@@ -1356,10 +1406,29 @@ static struct cpufreq_driver amd_pstate_epp_driver = {
 	.online		= amd_pstate_epp_cpu_online,
 	.suspend	= amd_pstate_epp_suspend,
 	.resume		= amd_pstate_epp_resume,
-	.name		= "amd_pstate_epp",
+	.name		= "amd-pstate-epp",
 	.attr		= amd_pstate_epp_attr,
 };
 
+static int __init amd_pstate_set_driver(int mode_idx)
+{
+	if (mode_idx >= AMD_PSTATE_DISABLE && mode_idx < AMD_PSTATE_MAX) {
+		cppc_state = mode_idx;
+		if (cppc_state == AMD_PSTATE_DISABLE)
+			pr_info("driver is explicitly disabled\n");
+
+		if (cppc_state == AMD_PSTATE_ACTIVE)
+			current_pstate_driver = &amd_pstate_epp_driver;
+
+		if (cppc_state == AMD_PSTATE_PASSIVE || cppc_state == AMD_PSTATE_GUIDED)
+			current_pstate_driver = &amd_pstate_driver;
+
+		return 0;
+	}
+
+	return -EINVAL;
+}
+
 static int __init amd_pstate_init(void)
 {
 	struct device *dev_root;
@@ -1367,15 +1436,6 @@ static int __init amd_pstate_init(void)
 
 	if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD)
 		return -ENODEV;
-	/*
-	 * by default the pstate driver is disabled to load
-	 * enable the amd_pstate passive mode driver explicitly
-	 * with amd_pstate=passive or other modes in kernel command line
-	 */
-	if (cppc_state == AMD_PSTATE_DISABLE) {
-		pr_info("driver load is disabled, boot with specific mode to enable this\n");
-		return -ENODEV;
-	}
 
 	if (!acpi_cpc_valid()) {
 		pr_warn_once("the _CPC object is not present in SBIOS or ACPI disabled\n");
@@ -1386,6 +1446,33 @@ static int __init amd_pstate_init(void)
 	if (cpufreq_get_current_driver())
 		return -EEXIST;
 
+	switch (cppc_state) {
+	case AMD_PSTATE_UNDEFINED:
+		/* Disable on the following configs by default:
+		 * 1. Undefined platforms
+		 * 2. Server platforms
+		 * 3. Shared memory designs
+		 */
+		if (amd_pstate_acpi_pm_profile_undefined() ||
+		    amd_pstate_acpi_pm_profile_server() ||
+		    !boot_cpu_has(X86_FEATURE_CPPC)) {
+			pr_info("driver load is disabled, boot with specific mode to enable this\n");
+			return -ENODEV;
+		}
+		ret = amd_pstate_set_driver(CONFIG_X86_AMD_PSTATE_DEFAULT_MODE);
+		if (ret)
+			return ret;
+		break;
+	case AMD_PSTATE_DISABLE:
+		return -ENODEV;
+	case AMD_PSTATE_PASSIVE:
+	case AMD_PSTATE_ACTIVE:
+	case AMD_PSTATE_GUIDED:
+		break;
+	default:
+		return -EINVAL;
+	}
+
 	/* capability check */
 	if (boot_cpu_has(X86_FEATURE_CPPC)) {
 		pr_debug("AMD CPPC MSR based functionality is supported\n");
@@ -1438,21 +1525,7 @@ static int __init amd_pstate_param(char *str)
 	size = strlen(str);
 	mode_idx = get_mode_idx_from_str(str, size);
 
-	if (mode_idx >= AMD_PSTATE_DISABLE && mode_idx < AMD_PSTATE_MAX) {
-		cppc_state = mode_idx;
-		if (cppc_state == AMD_PSTATE_DISABLE)
-			pr_info("driver is explicitly disabled\n");
-
-		if (cppc_state == AMD_PSTATE_ACTIVE)
-			current_pstate_driver = &amd_pstate_epp_driver;
-
-		if (cppc_state == AMD_PSTATE_PASSIVE || cppc_state == AMD_PSTATE_GUIDED)
-			current_pstate_driver = &amd_pstate_driver;
-
-		return 0;
-	}
-
-	return -EINVAL;
+	return amd_pstate_set_driver(mode_idx);
 }
 early_param("amd_pstate", amd_pstate_param);
 

drivers/cpufreq/cpufreq.c

@@ -2828,7 +2828,8 @@ int cpufreq_register_driver(struct cpufreq_driver *driver_data)
 	     (driver_data->setpolicy && (driver_data->target_index ||
 		    driver_data->target)) ||
 	     (!driver_data->get_intermediate != !driver_data->target_intermediate) ||
-	     (!driver_data->online != !driver_data->offline))
+	     (!driver_data->online != !driver_data->offline) ||
+		 (driver_data->adjust_perf && !driver_data->fast_switch))
 		return -EINVAL;
 
 	pr_debug("trying to register driver %s\n", driver_data->name);

drivers/cpufreq/intel_pstate.c

@@ -824,6 +824,8 @@ static ssize_t store_energy_performance_preference(
 			err = cpufreq_start_governor(policy);
 			if (!ret)
 				ret = err;
+		} else {
+			ret = 0;
 		}
 	}
 

drivers/idle/intel_idle.c

@@ -199,6 +199,43 @@ static __cpuidle int intel_idle_xstate(struct cpuidle_device *dev,
 	return __intel_idle(dev, drv, index);
 }
 
+static __always_inline int __intel_idle_hlt(struct cpuidle_device *dev,
+					struct cpuidle_driver *drv, int index)
+{
+	raw_safe_halt();
+	raw_local_irq_disable();
+	return index;
+}
+
+/**
+ * intel_idle_hlt - Ask the processor to enter the given idle state using hlt.
+ * @dev: cpuidle device of the target CPU.
+ * @drv: cpuidle driver (assumed to point to intel_idle_driver).
+ * @index: Target idle state index.
+ *
+ * Use the HLT instruction to notify the processor that the CPU represented by
+ * @dev is idle and it can try to enter the idle state corresponding to @index.
+ *
+ * Must be called under local_irq_disable().
+ */
+static __cpuidle int intel_idle_hlt(struct cpuidle_device *dev,
+				struct cpuidle_driver *drv, int index)
+{
+	return __intel_idle_hlt(dev, drv, index);
+}
+
+static __cpuidle int intel_idle_hlt_irq_on(struct cpuidle_device *dev,
+                                   struct cpuidle_driver *drv, int index)
+{
+       int ret;
+
+       raw_local_irq_enable();
+       ret = __intel_idle_hlt(dev, drv, index);
+       raw_local_irq_disable();
+
+       return ret;
+}
+
 /**
  * intel_idle_s2idle - Ask the processor to enter the given idle state.
  * @dev: cpuidle device of the target CPU.
@@ -1242,6 +1279,25 @@ static struct cpuidle_state snr_cstates[] __initdata = {
 		.enter = NULL }
 };
 
+static struct cpuidle_state vmguest_cstates[] __initdata = {
+	{
+		.name = "C1",
+		.desc = "HLT",
+		.flags = MWAIT2flg(0x00) | CPUIDLE_FLAG_IRQ_ENABLE,
+		.exit_latency = 5,
+		.target_residency = 10,
+		.enter = &intel_idle_hlt, },
+	{
+		.name = "C1L",
+		.desc = "Long HLT",
+		.flags = MWAIT2flg(0x00) | CPUIDLE_FLAG_TLB_FLUSHED,
+		.exit_latency = 5,
+		.target_residency = 200,
+		.enter = &intel_idle_hlt, },
+	{
+		.enter = NULL }
+};
+
 static const struct idle_cpu idle_cpu_nehalem __initconst = {
 	.state_table = nehalem_cstates,
 	.auto_demotion_disable_flags = NHM_C1_AUTO_DEMOTE | NHM_C3_AUTO_DEMOTE,
@@ -1839,6 +1895,66 @@ static bool __init intel_idle_verify_cstate(unsigned int mwait_hint)
 	return true;
 }
 
+static void state_update_enter_method(struct cpuidle_state *state, int cstate)
+{
+	if (state->enter == intel_idle_hlt) {
+		if (force_irq_on) {
+			pr_info("forced intel_idle_irq for state %d\n", cstate);
+			state->enter = intel_idle_hlt_irq_on;
+		}
+		return;
+	}
+	if (state->enter == intel_idle_hlt_irq_on)
+		return; /* no update scenarios */
+
+	if (state->flags & CPUIDLE_FLAG_INIT_XSTATE) {
+		/*
+		 * Combining with XSTATE with IBRS or IRQ_ENABLE flags
+		 * is not currently supported but this driver.
+		 */
+		WARN_ON_ONCE(state->flags & CPUIDLE_FLAG_IBRS);
+		WARN_ON_ONCE(state->flags & CPUIDLE_FLAG_IRQ_ENABLE);
+		state->enter = intel_idle_xstate;
+		return;
+	}
+
+	if (cpu_feature_enabled(X86_FEATURE_KERNEL_IBRS) &&
+			   state->flags & CPUIDLE_FLAG_IBRS) {
+		/*
+		 * IBRS mitigation requires that C-states are entered
+		 * with interrupts disabled.
+		 */
+		WARN_ON_ONCE(state->flags & CPUIDLE_FLAG_IRQ_ENABLE);
+		state->enter = intel_idle_ibrs;
+		return;
+	}
+
+	if (state->flags & CPUIDLE_FLAG_IRQ_ENABLE) {
+		state->enter = intel_idle_irq;
+		return;
+	}
+
+	if (force_irq_on) {
+		pr_info("forced intel_idle_irq for state %d\n", cstate);
+		state->enter = intel_idle_irq;
+	}
+}
+
+/*
+ * For mwait based states, we want to verify the cpuid data to see if the state
+ * is actually supported by this specific CPU.
+ * For non-mwait based states, this check should be skipped.
+ */
+static bool should_verify_mwait(struct cpuidle_state *state)
+{
+	if (state->enter == intel_idle_hlt)
+		return false;
+	if (state->enter == intel_idle_hlt_irq_on)
+		return false;
+
+	return true;
+}
+
 static void __init intel_idle_init_cstates_icpu(struct cpuidle_driver *drv)
 {
 	int cstate;
@@ -1887,35 +2003,15 @@ static void __init intel_idle_init_cstates_icpu(struct cpuidle_driver *drv)
 		}
 
 		mwait_hint = flg2MWAIT(cpuidle_state_table[cstate].flags);
-		if (!intel_idle_verify_cstate(mwait_hint))
+		if (should_verify_mwait(&cpuidle_state_table[cstate]) && !intel_idle_verify_cstate(mwait_hint))
 			continue;
 
 		/* Structure copy. */
 		drv->states[drv->state_count] = cpuidle_state_table[cstate];
 		state = &drv->states[drv->state_count];
 
-		if (state->flags & CPUIDLE_FLAG_INIT_XSTATE) {
-			/*
-			 * Combining with XSTATE with IBRS or IRQ_ENABLE flags
-			 * is not currently supported but this driver.
-			 */
-			WARN_ON_ONCE(state->flags & CPUIDLE_FLAG_IBRS);
-			WARN_ON_ONCE(state->flags & CPUIDLE_FLAG_IRQ_ENABLE);
-			state->enter = intel_idle_xstate;
-		} else if (cpu_feature_enabled(X86_FEATURE_KERNEL_IBRS) &&
-			   state->flags & CPUIDLE_FLAG_IBRS) {
-			/*
-			 * IBRS mitigation requires that C-states are entered
-			 * with interrupts disabled.
-			 */
-			WARN_ON_ONCE(state->flags & CPUIDLE_FLAG_IRQ_ENABLE);
-			state->enter = intel_idle_ibrs;
-		} else if (state->flags & CPUIDLE_FLAG_IRQ_ENABLE) {
-			state->enter = intel_idle_irq;
-		} else if (force_irq_on) {
-			pr_info("forced intel_idle_irq for state %d\n", cstate);
-			state->enter = intel_idle_irq;
-		}
+		state_update_enter_method(state, cstate);
+
 
 		if ((disabled_states_mask & BIT(drv->state_count)) ||
 		    ((icpu->use_acpi || force_use_acpi) &&
@@ -2041,6 +2137,93 @@ static void __init intel_idle_cpuidle_devices_uninit(void)
 		cpuidle_unregister_device(per_cpu_ptr(intel_idle_cpuidle_devices, i));
 }
 
+/*
+ * Match up the latency and break even point of the bare metal (cpu based)
+ * states with the deepest VM available state.
+ *
+ * We only want to do this for the deepest state, the ones that has
+ * the TLB_FLUSHED flag set on the .
+ *
+ * All our short idle states are dominated by vmexit/vmenter latencies,
+ * not the underlying hardware latencies so we keep our values for these.
+ */
+static void matchup_vm_state_with_baremetal(void)
+{
+	int cstate;
+
+	for (cstate = 0; cstate < CPUIDLE_STATE_MAX; ++cstate) {
+		int matching_cstate;
+
+		if (intel_idle_max_cstate_reached(cstate))
+			break;
+
+		if (!cpuidle_state_table[cstate].enter)
+			break;
+
+		if (!(cpuidle_state_table[cstate].flags & CPUIDLE_FLAG_TLB_FLUSHED))
+			continue;
+
+		for (matching_cstate = 0; matching_cstate < CPUIDLE_STATE_MAX; ++matching_cstate) {
+			if (!icpu->state_table[matching_cstate].enter)
+				break;
+			if (icpu->state_table[matching_cstate].exit_latency > cpuidle_state_table[cstate].exit_latency) {
+				cpuidle_state_table[cstate].exit_latency = icpu->state_table[matching_cstate].exit_latency;
+				cpuidle_state_table[cstate].target_residency = icpu->state_table[matching_cstate].target_residency;
+			}
+		}
+
+	}
+}
+
+
+static int __init intel_idle_vminit(const struct x86_cpu_id *id)
+{
+	int retval;
+
+	cpuidle_state_table = vmguest_cstates;
+
+	icpu = (const struct idle_cpu *)id->driver_data;
+
+	pr_debug("v" INTEL_IDLE_VERSION " model 0x%X\n",
+		 boot_cpu_data.x86_model);
+
+	intel_idle_cpuidle_devices = alloc_percpu(struct cpuidle_device);
+	if (!intel_idle_cpuidle_devices)
+		return -ENOMEM;
+
+	/*
+	 * We don't know exactly what the host will do when we go idle, but as a worst estimate
+	 * we can assume that the exit latency of the deepest host state will be hit for our
+	 * deep (long duration) guest idle state.
+	 * The same logic applies to the break even point for the long duration guest idle state.
+	 * So lets copy these two properties from the table we found for the host CPU type.
+	 */
+	matchup_vm_state_with_baremetal();
+
+	intel_idle_cpuidle_driver_init(&intel_idle_driver);
+
+	retval = cpuidle_register_driver(&intel_idle_driver);
+	if (retval) {
+		struct cpuidle_driver *drv = cpuidle_get_driver();
+		printk(KERN_DEBUG pr_fmt("intel_idle yielding to %s\n"),
+		       drv ? drv->name : "none");
+		goto init_driver_fail;
+	}
+
+	retval = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "idle/intel:online",
+				   intel_idle_cpu_online, NULL);
+	if (retval < 0)
+		goto hp_setup_fail;
+
+	return 0;
+hp_setup_fail:
+	intel_idle_cpuidle_devices_uninit();
+	cpuidle_unregister_driver(&intel_idle_driver);
+init_driver_fail:
+	free_percpu(intel_idle_cpuidle_devices);
+	return retval;
+}
+
 static int __init intel_idle_init(void)
 {
 	const struct x86_cpu_id *id;
@@ -2059,6 +2242,8 @@ static int __init intel_idle_init(void)
 	id = x86_match_cpu(intel_idle_ids);
 	if (id) {
 		if (!boot_cpu_has(X86_FEATURE_MWAIT)) {
+			if (boot_cpu_has(X86_FEATURE_HYPERVISOR))
+				return intel_idle_vminit(id);
 			pr_debug("Please enable MWAIT in BIOS SETUP\n");
 			return -ENODEV;
 		}

include/acpi/actbl.h

@@ -307,7 +307,8 @@ enum acpi_preferred_pm_profiles {
 	PM_SOHO_SERVER = 5,
 	PM_APPLIANCE_PC = 6,
 	PM_PERFORMANCE_SERVER = 7,
-	PM_TABLET = 8
+	PM_TABLET = 8,
+	NR_PM_PROFILES = 9
 };
 
 /* Values for sleep_status and sleep_control registers (V5+ FADT) */

include/linux/amd-pstate.h

@@ -94,7 +94,8 @@ struct amd_cpudata {
  * enum amd_pstate_mode - driver working mode of amd pstate
  */
 enum amd_pstate_mode {
-	AMD_PSTATE_DISABLE = 0,
+	AMD_PSTATE_UNDEFINED = 0,
+	AMD_PSTATE_DISABLE,
 	AMD_PSTATE_PASSIVE,
 	AMD_PSTATE_ACTIVE,
 	AMD_PSTATE_GUIDED,
@@ -102,6 +103,7 @@ enum amd_pstate_mode {
 };
 
 static const char * const amd_pstate_mode_string[] = {
+	[AMD_PSTATE_UNDEFINED]   = "undefined",
 	[AMD_PSTATE_DISABLE]     = "disable",
 	[AMD_PSTATE_PASSIVE]     = "passive",
 	[AMD_PSTATE_ACTIVE]      = "active",

include/linux/cpufreq.h

@@ -340,7 +340,10 @@ struct cpufreq_driver {
 	/*
 	 * ->fast_switch() replacement for drivers that use an internal
 	 * representation of performance levels and can pass hints other than
-	 * the target performance level to the hardware.
+	 * the target performance level to the hardware. This can only be set
+	 * if ->fast_switch is set too, because in those cases (under specific
+	 * conditions) scale invariance can be disabled, which causes the
+	 * schedutil governor to fall back to the latter.
 	 */
 	void		(*adjust_perf)(unsigned int cpu,
 				       unsigned long min_perf,