intel_idle: Provide the default enter_dead() handler

Recent Intel platforms require idle driver to provide information about
the MWAIT hint used to enter the deepest idle state in the play_dead
code.

Provide the default enter_dead() handler for all of the platforms and
allow overwriting with a custom handler for each platform if needed.

Signed-off-by: Patryk Wlazlyn <patryk.wlazlyn@linux.intel.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Link: https://lore.kernel.org/all/20250205155211.329780-4-artem.bityutskiy%40linux.intel.com

Author: Patryk Wlazlyn

drivers/idle/intel_idle.c

@@ -57,6 +57,7 @@
 #include <asm/mwait.h>
 #include <asm/spec-ctrl.h>
 #include <asm/fpu/api.h>
+#include <asm/smp.h>
 
 #define INTEL_IDLE_VERSION "0.5.1"
 
@@ -228,6 +229,15 @@ static __cpuidle int intel_idle_s2idle(struct cpuidle_device *dev,
 	return 0;
 }
 
+static void intel_idle_enter_dead(struct cpuidle_device *dev, int index)
+{
+	struct cpuidle_driver *drv = cpuidle_get_cpu_driver(dev);
+	struct cpuidle_state *state = &drv->states[index];
+	unsigned long eax = flg2MWAIT(state->flags);
+
+	mwait_play_dead(eax);
+}
+
 /*
  * States are indexed by the cstate number,
  * which is also the index into the MWAIT hint array.
@@ -1800,6 +1810,7 @@ static void __init intel_idle_init_cstates_acpi(struct cpuidle_driver *drv)
 			state->flags |= CPUIDLE_FLAG_TIMER_STOP;
 
 		state->enter = intel_idle;
+		state->enter_dead = intel_idle_enter_dead;
 		state->enter_s2idle = intel_idle_s2idle;
 	}
 }
@@ -2149,6 +2160,9 @@ static void __init intel_idle_init_cstates_icpu(struct cpuidle_driver *drv)
 		    !cpuidle_state_table[cstate].enter_s2idle)
 			break;
 
+		if (!cpuidle_state_table[cstate].enter_dead)
+			cpuidle_state_table[cstate].enter_dead = intel_idle_enter_dead;
+
 		/* If marked as unusable, skip this state. */
 		if (cpuidle_state_table[cstate].flags & CPUIDLE_FLAG_UNUSABLE) {
 			pr_debug("state %s is disabled\n",