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Subject[PATCH v2 1/2] intel_idle: Introduce 'use_acpi' module parameter
From: Rafael J. Wysocki <>

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

Signed-off-by: Rafael J. Wysocki <>

-> v2:
* Fix build for CONFIG_ACPI unset.

Documentation/admin-guide/pm/intel_idle.rst | 13 +++++++++----
drivers/idle/intel_idle.c | 11 +++++++++--
2 files changed, 18 insertions(+), 6 deletions(-)

Index: linux-pm/drivers/idle/intel_idle.c
--- linux-pm.orig/drivers/idle/intel_idle.c
+++ linux-pm/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_def
return true;
+#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_cstat
/* 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)
} else if (!intel_idle_acpi_cst_extract()) {
return -ENODEV;
Index: linux-pm/Documentation/admin-guide/pm/intel_idle.rst
--- linux-pm.orig/Documentation/admin-guide/pm/intel_idle.rst
+++ linux-pm/Documentation/admin-guide/pm/intel_idle.rst
@@ -60,6 +60,9 @@ of the system. The former are always us
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
``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 ``CP
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:

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