[PATCH 4/7] intel_idle: Add helper functions to support 'hlt' as idle state

[arjan@linux.intel.com]

From: Arjan van de Ven <arjan.van.de.ven@intel.com>

Currently the intel_idle driver has a family of functions called
intel_idle/intel_idle_irq/intel_idle_xsave/... that use the
mwait instruction to enter into a low power state.

x86 cpus can also use the legacy "hlt" instruction for this,
and in some cases (VM guests for example) the mwait instruction
might not be available.

Because of this, add the basic helpers to allow 'hlt' to be used to enter
a low power state (will be used in later patches), both in the
regular and the _irq enabled variant.

Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
---
 drivers/idle/intel_idle.c | 37 +++++++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)

diff --git a/drivers/idle/intel_idle.c b/drivers/idle/intel_idle.c
index 8415965372c7..66d262fd267e 100644
--- a/drivers/idle/intel_idle.c
+++ b/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(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.
-- 
2.40.1