[PATCH v5] intel_idle: introduce 'no_native' module parameter

[David Arcari <darcari@redhat.com>]

Since commit 18734958e9bf ("intel_idle: Use ACPI _CST for processor models
without C-state tables") the intel_idle driver has had the ability to use
the ACPI _CST to populate C-states when the processor model is not
recognized. However, even when the processor model is recognized (native
mode) there are cases where it is useful to make the driver ignore the per
cpu idle states in lieu of ACPI C-states (such as specific application
performance). Add the 'no_native' module parameter to provide this
functionality.

Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Jacob Pan <jacob.jun.pan@linux.intel.com>
Cc: Len Brown <lenb@kernel.org>
Cc: David Arcari <darcari@redhat.com>
Cc: Artem Bityutskiy <dedekind1@gmail.com>
Cc: Prarit Bhargava <prarit@redhat.com>
Cc: linux-doc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: David Arcari <darcari@redhat.com>
---
v5: if statement simplication, also add missing '&' to ignore_native()
v4: fix !CONFIG_ACPI_PROCESSOR_CSTATE compilation issue
v3: more documentation cleanup
v2: renamed parameter, cleaned up documentation

 Documentation/admin-guide/pm/intel_idle.rst | 18 +++++++++++++-----
 drivers/idle/intel_idle.c                   | 14 ++++++++++++++
 2 files changed, 27 insertions(+), 5 deletions(-)

diff --git a/Documentation/admin-guide/pm/intel_idle.rst b/Documentation/admin-guide/pm/intel_idle.rst
index 39bd6ecce7de..5940528146eb 100644
--- a/Documentation/admin-guide/pm/intel_idle.rst
+++ b/Documentation/admin-guide/pm/intel_idle.rst
@@ -192,11 +192,19 @@ even if they have been enumerated (see :ref:`cpu-pm-qos` in
 Documentation/admin-guide/pm/cpuidle.rst).
 Setting ``max_cstate`` to 0 causes the ``intel_idle`` initialization to fail.
 
-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).
+The ``no_acpi``, ``use_acpi`` and ``no_native`` module parameters are
+recognized by ``intel_idle`` if the kernel has been configured with ACPI
+support.  In the case that ACPI is not configured these flags have no impact
+on functionality.
+
+``no_acpi`` - Do not use ACPI at all.  Only native mode is available, no
+ACPI mode.
+
+``use_acpi`` - No-op in ACPI mode, the driver will consult ACPI tables for
+C-states on/off status in native mode.
+
+``no_native`` - Work only in ACPI mode, no native mode available (ignore
+all custom tables).
 
 The value of the ``states_off`` module parameter (0 by default) represents a
 list of idle states to be disabled by default in the form of a bitmask.
diff --git a/drivers/idle/intel_idle.c b/drivers/idle/intel_idle.c
index 118fe1d37c22..d0b23ea03e6f 100644
--- a/drivers/idle/intel_idle.c
+++ b/drivers/idle/intel_idle.c
@@ -1695,6 +1695,10 @@ 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 bool no_native __read_mostly; /* No effect if no_acpi is set. */
+module_param_named(no_native, no_native, bool, 0444);
+MODULE_PARM_DESC(no_native, "Ignore cpu specific (native) idle states in lieu of ACPI idle states");
+
 static struct acpi_processor_power acpi_state_table __initdata;
 
 /**
@@ -1834,6 +1838,11 @@ static bool __init intel_idle_off_by_default(unsigned int flags, u32 mwait_hint)
 	}
 	return true;
 }
+
+static inline bool ignore_native(void)
+{
+	return no_native && !no_acpi;
+}
 #else /* !CONFIG_ACPI_PROCESSOR_CSTATE */
 #define force_use_acpi	(false)
 
@@ -1843,6 +1852,7 @@ static inline bool intel_idle_off_by_default(unsigned int flags, u32 mwait_hint)
 {
 	return false;
 }
+static inline bool ignore_native(void) { return false; }
 #endif /* !CONFIG_ACPI_PROCESSOR_CSTATE */
 
 /**
@@ -2328,6 +2338,10 @@ static int __init intel_idle_init(void)
 	pr_debug("MWAIT substates: 0x%x\n", mwait_substates);
 
 	icpu = (const struct idle_cpu *)id->driver_data;
+	if (icpu && ignore_native()) {
+		pr_debug("ignoring native cpu idle states\n");
+		icpu = NULL;
+	}
 	if (icpu) {
 		if (icpu->state_table)
 			cpuidle_state_table = icpu->state_table;
-- 
2.48.1