intel_idle: Introduce 'use_acpi' module parameter

For diagnostics, it is generally useful to be able to make intel_idle
take the system's ACPI tables into consideration even if that is not
required for the processor model in there, so introduce a new module
parameter, 'use_acpi', to make that happen and update the documentation
to cover it.

While at it, fix the 'no_acpi' module parameter name in the
documentation.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Documentation/admin-guide/pm/intel_idle.rst

@@ -60,6 +60,9 @@ of the system.  The former are always used if the processor model at hand is
 recognized by ``intel_idle`` and the latter are used if that is required for
 the given processor model (which is the case for all server processor models
 recognized by ``intel_idle``) or if the processor model is not recognized.
+[There is a module parameter that can be used to make the driver use the ACPI
+tables with any processor model recognized by it; see
+`below <intel-idle-parameters_>`_.]
 
 If the ACPI tables are going to be used for building the list of available idle
 states, ``intel_idle`` first looks for a ``_CST`` object under one of the ACPI
@@ -165,7 +168,7 @@ and ``idle=nomwait``.  If any of them is present in the kernel command line, the
 ``MWAIT`` instruction is not allowed to be used, so the initialization of
 ``intel_idle`` will fail.
 
-Apart from that there are two module parameters recognized by ``intel_idle``
+Apart from that there are three module parameters recognized by ``intel_idle``
 itself that can be set via the kernel command line (they cannot be updated via
 sysfs, so that is the only way to change their values).
 
@@ -186,9 +189,11 @@ QoS) feature can be used to prevent ``CPUIdle`` from touching those idle states
 even if they have been enumerated (see :ref:`cpu-pm-qos` in :doc:`cpuidle`).
 Setting ``max_cstate`` to 0 causes the ``intel_idle`` initialization to fail.
 
-The ``noacpi`` module parameter (which is recognized by ``intel_idle`` if the
-kernel has been configured with ACPI support), can be set to make the driver
-ignore the system's ACPI tables entirely (it is unset by default).
+The ``no_acpi`` and ``use_acpi`` module parameters (recognized by ``intel_idle``
+if the kernel has been configured with ACPI support) can be set to make the
+driver ignore the system's ACPI tables entirely or use them for all of the
+recognized processor models, respectively (they both are unset by default and
+``use_acpi`` has no effect if ``no_acpi`` is set).
 
 
 .. _intel-idle-core-and-package-idle-states:

drivers/idle/intel_idle.c

@@ -1131,6 +1131,10 @@ static bool no_acpi __read_mostly;
 module_param(no_acpi, bool, 0444);
 MODULE_PARM_DESC(no_acpi, "Do not use ACPI _CST for building the idle states list");
 
+static bool force_use_acpi __read_mostly; /* No effect if no_acpi is set. */
+module_param_named(use_acpi, force_use_acpi, bool, 0444);
+MODULE_PARM_DESC(use_acpi, "Use ACPI _CST for building the idle states list");
+
 static struct acpi_processor_power acpi_state_table __initdata;
 
 /**
@@ -1258,6 +1262,8 @@ static bool __init intel_idle_off_by_default(u32 mwait_hint)
 	return true;
 }
 #else /* !CONFIG_ACPI_PROCESSOR_CSTATE */
+#define force_use_acpi	(false)
+
 static inline bool intel_idle_acpi_cst_extract(void) { return false; }
 static inline void intel_idle_init_cstates_acpi(struct cpuidle_driver *drv) { }
 static inline bool intel_idle_off_by_default(u32 mwait_hint) { return false; }
@@ -1460,7 +1466,8 @@ static void __init intel_idle_init_cstates_icpu(struct cpuidle_driver *drv)
 		/* Structure copy. */
 		drv->states[drv->state_count] = cpuidle_state_table[cstate];
 
-		if (icpu->use_acpi && intel_idle_off_by_default(mwait_hint) &&
+		if ((icpu->use_acpi || force_use_acpi) &&
+		    intel_idle_off_by_default(mwait_hint) &&
 		    !(cpuidle_state_table[cstate].flags & CPUIDLE_FLAG_ALWAYS_ENABLE))
 			drv->states[drv->state_count].flags |= CPUIDLE_FLAG_OFF;
 
@@ -1607,7 +1614,7 @@ static int __init intel_idle_init(void)
 	icpu = (const struct idle_cpu *)id->driver_data;
 	if (icpu) {
 		cpuidle_state_table = icpu->state_table;
-		if (icpu->use_acpi)
+		if (icpu->use_acpi || force_use_acpi)
 			intel_idle_acpi_cst_extract();
 	} else if (!intel_idle_acpi_cst_extract()) {
 		return -ENODEV;