intel_idle: native hardware cpuidle driver for latest Intel processors

This EXPERIMENTAL driver supersedes acpi_idle on
Intel Atom Processors, Intel Core i3/i5/i7 Processors
and associated Intel Xeon processors.

It does not support the Intel Core2 processor or earlier.

For kernels configured with ACPI, CONFIG_INTEL_IDLE=y
allows intel_idle to probe before the ACPI processor driver.
Booting with "intel_idle.max_cstate=0" disables intel_idle
and the system will fall back on ACPI's "acpi_idle".

Typical Linux distributions load ACPI processor module early,
making CONFIG_INTEL_IDLE=m not easily useful on ACPI platforms.

intel_idle probes all processors at module_init time.
Processors that are hot-added later will be limited
to using C1 in idle.

Signed-off-by: Len Brown <len.brown@intel.com>

drivers/acpi/processor_driver.c

@@ -922,9 +922,13 @@ static int __init acpi_processor_init(void)
 		return -ENOMEM;
 #endif
 
-	if (!cpuidle_register_driver(&acpi_idle_driver))
+	if (!cpuidle_register_driver(&acpi_idle_driver)) {
 		printk(KERN_DEBUG "ACPI: %s registered with cpuidle\n",
 			acpi_idle_driver.name);
+	} else {
+		printk(KERN_DEBUG "ACPI: acpi_idle yielding to %s",
+			cpuidle_get_driver()->name);
+	}
 
 	result = acpi_bus_register_driver(&acpi_processor_driver);
 	if (result < 0)