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 <[e-mail]>

MAINTAINERS

···
 S:	Maintained
 F:	drivers/input/
 
+INTEL IDLE DRIVER
+M:	Len Brown <[e-mail]>
+L:	[e-mail]
+T:	git git://git.kernel.org/pub/scm/linux/kernel/git/lenb/linux-idle-2.6.git
+S:	Supported
+F:	drivers/idle/intel_idle.c
+
 INTEL FRAMEBUFFER DRIVER (excluding 810 and 815)
 M:	Maik Broemme <[e-mail]>
 L:	[e-mail]

drivers/Makefile

···
 obj-$(CONFIG_PARISC)		+= parisc/
 obj-$(CONFIG_RAPIDIO)		+= rapidio/
 obj-y				+= video/
+obj-y				+= idle/
 obj-$(CONFIG_ACPI)		+= acpi/
 obj-$(CONFIG_SFI)		+= sfi/
 # PnP must come after ACPI since it will eventually need to check if acpi
···
 obj-y				+= lguest/
 obj-$(CONFIG_CPU_FREQ)		+= cpufreq/
 obj-$(CONFIG_CPU_IDLE)		+= cpuidle/
-obj-y				+= idle/
 obj-$(CONFIG_MMC)		+= mmc/
 obj-$(CONFIG_MEMSTICK)		+= memstick/
 obj-$(CONFIG_NEW_LEDS)		+= leds/

drivers/acpi/processor_driver.c

···
 		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)

drivers/idle/Kconfig

···
+config INTEL_IDLE
+	tristate "Cpuidle Driver for Intel Processors"
+	depends on CPU_IDLE
+	depends on X86
+	depends on CPU_SUP_INTEL
+	depends on EXPERIMENTAL
+	help
+	  Enable intel_idle, a cpuidle driver that includes knowledge of
+	  native Intel hardware idle features.  The acpi_idle driver
+	  can be configured at the same time, in order to handle
+	  processors intel_idle does not support.
 
 menu "Memory power savings"
 depends on X86_64

drivers/idle/Makefile

···
 obj-$(CONFIG_I7300_IDLE)			+= i7300_idle.o
+obj-$(CONFIG_INTEL_IDLE)			+= intel_idle.o
 

drivers/idle/intel_idle.c

···
+/*
+ * intel_idle.c - native hardware idle loop for modern Intel processors
+ *
+ * Copyright (c) 2010, Intel Corporation.
+ * Len Brown <[e-mail]>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin St - Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+/*
+ * intel_idle is a cpuidle driver that loads on specific Intel processors
+ * in lieu of the legacy ACPI processor_idle driver.  The intent is to
+ * make Linux more efficient on these processors, as intel_idle knows
+ * more than ACPI, as well as make Linux more immune to ACPI BIOS bugs.
+ */
+
+/*
+ * Design Assumptions
+ *
+ * All CPUs have same idle states as boot CPU
+ *
+ * Chipset BM_STS (bus master status) bit is a NOP
+ *	for preventing entry into deep C-stats
+ */
+
+/*
+ * Known limitations
+ *
+ * The driver currently initializes for_each_online_cpu() upon modprobe.
+ * It it unaware of subsequent processors hot-added to the system.
+ * This means that if you boot with maxcpus=n and later online
+ * processors above n, those processors will use C1 only.
+ *
+ * ACPI has a .suspend hack to turn off deep c-statees during suspend
+ * to avoid complications with the lapic timer workaround.
+ * Have not seen issues with suspend, but may need same workaround here.
+ *
+ * There is currently no kernel-based automatic probing/loading mechanism
+ * if the driver is built as a module.
+ */
+
+/* un-comment DEBUG to enable pr_debug() statements */
+#define DEBUG
+
+#include <linux/kernel.h>
+#include <linux/cpuidle.h>
+#include <linux/clockchips.h>
+#include <linux/hrtimer.h>	/* ktime_get_real() */
+#include <trace/events/power.h>
+#include <linux/sched.h>
+
+#define INTEL_IDLE_VERSION "0.4"
+#define PREFIX "intel_idle: "
+
+#define MWAIT_SUBSTATE_MASK	(0xf)
+#define MWAIT_CSTATE_MASK	(0xf)
+#define MWAIT_SUBSTATE_SIZE	(4)
+#define MWAIT_MAX_NUM_CSTATES	8
+#define CPUID_MWAIT_LEAF (5)
+#define CPUID5_ECX_EXTENSIONS_SUPPORTED (0x1)
+#define CPUID5_ECX_INTERRUPT_BREAK	(0x2)
+
+static struct cpuidle_driver intel_idle_driver = {
+	.name = "intel_idle",
+	.owner = THIS_MODULE,
+};
+/* intel_idle.max_cstate=0 disables driver */
+static int max_cstate = MWAIT_MAX_NUM_CSTATES - 1;
+static int power_policy = 7; /* 0 = max perf; 15 = max powersave */
+
+static unsigned int substates;
+static int (*choose_substate)(int);
+
+/* Reliable LAPIC Timer States, bit 1 for C1 etc.  */
+static unsigned int lapic_timer_reliable_states;
+
+static struct cpuidle_device *intel_idle_cpuidle_devices;
+static int intel_idle(struct cpuidle_device *dev, struct cpuidle_state *state);
+
+static struct cpuidle_state *cpuidle_state_table;
+
+/*
+ * States are indexed by the cstate number,
+ * which is also the index into the MWAIT hint array.
+ * Thus C0 is a dummy.
+ */
+static struct cpuidle_state nehalem_cstates[MWAIT_MAX_NUM_CSTATES] = {
+	{ /* MWAIT C0 */ },
+	{ /* MWAIT C1 */
+		.name = "NHM-C1",
+		.desc = "MWAIT 0x00",
+		.driver_data = (void *) 0x00,
+		.flags = CPUIDLE_FLAG_TIME_VALID,
+		.exit_latency = 3,
+		.power_usage = 1000,
+		.target_residency = 6,
+		.enter = &intel_idle },
+	{ /* MWAIT C2 */
+		.name = "NHM-C3",
+		.desc = "MWAIT 0x10",
+		.driver_data = (void *) 0x10,
+		.flags = CPUIDLE_FLAG_TIME_VALID,
+		.exit_latency = 20,
+		.power_usage = 500,
+		.target_residency = 80,
+		.enter = &intel_idle },
+	{ /* MWAIT C3 */
+		.name = "NHM-C6",
+		.desc = "MWAIT 0x20",
+		.driver_data = (void *) 0x20,
+		.flags = CPUIDLE_FLAG_TIME_VALID,
+		.exit_latency = 200,
+		.power_usage = 350,
+		.target_residency = 800,
+		.enter = &intel_idle },
+};
+
+static struct cpuidle_state atom_cstates[MWAIT_MAX_NUM_CSTATES] = {
+	{ /* MWAIT C0 */ },
+	{ /* MWAIT C1 */
+		.name = "ATM-C1",
+		.desc = "MWAIT 0x00",
+		.driver_data = (void *) 0x00,
+		.flags = CPUIDLE_FLAG_TIME_VALID,
+		.exit_latency = 1,
+		.power_usage = 1000,
+		.target_residency = 4,
+		.enter = &intel_idle },
+	{ /* MWAIT C2 */
+		.name = "ATM-C2",
+		.desc = "MWAIT 0x10",
+		.driver_data = (void *) 0x10,
+		.flags = CPUIDLE_FLAG_TIME_VALID,
+		.exit_latency = 20,
+		.power_usage = 500,
+		.target_residency = 80,
+		.enter = &intel_idle },
+	{ /* MWAIT C3 */ },
+	{ /* MWAIT C4 */
+		.name = "ATM-C4",
+		.desc = "MWAIT 0x30",
+		.driver_data = (void *) 0x30,
+		.flags = CPUIDLE_FLAG_TIME_VALID,
+		.exit_latency = 100,
+		.power_usage = 250,
+		.target_residency = 400,
+		.enter = &intel_idle },
+	{ /* MWAIT C5 */ },
+	{ /* MWAIT C6 */
+		.name = "ATM-C6",
+		.desc = "MWAIT 0x40",
+		.driver_data = (void *) 0x40,
+		.flags = CPUIDLE_FLAG_TIME_VALID,
+		.exit_latency = 200,
+		.power_usage = 150,
+		.target_residency = 800,
+		.enter = NULL },	/* disabled */
+};
+
+/*
+ * choose_tunable_substate()
+ *
+ * Run-time decision on which C-state substate to invoke
+ * If power_policy = 0, choose shallowest substate (0)
+ * If power_policy = 15, choose deepest substate
+ * If power_policy = middle, choose middle substate etc.
+ */
+static int choose_tunable_substate(int cstate)
+{
+	unsigned int num_substates;
+	unsigned int substate_choice;
+
+	power_policy &= 0xF;	/* valid range: 0-15 */
+	cstate &= 7;	/* valid range: 0-7 */
+
+	num_substates = (substates >> ((cstate) * 4)) & MWAIT_SUBSTATE_MASK;
+
+	if (num_substates <= 1)
+		return 0;
+
+	substate_choice = ((power_policy + (power_policy + 1) *
+				(num_substates - 1)) / 16);
+
+	return substate_choice;
+}
+
+/*
+ * choose_zero_substate()
+ */
+static int choose_zero_substate(int cstate)
+{
+	return 0;
+}
+
+/**
+ * intel_idle
+ * @dev: cpuidle_device
+ * @state: cpuidle state
+ *
+ */
+static int intel_idle(struct cpuidle_device *dev, struct cpuidle_state *state)
+{
+	unsigned long ecx = 1; /* break on interrupt flag */
+	unsigned long eax = (unsigned long)cpuidle_get_statedata(state);
+	unsigned int cstate;
+	ktime_t kt_before, kt_after;
+	s64 usec_delta;
+	int cpu = smp_processor_id();
+
+	cstate = (((eax) >> MWAIT_SUBSTATE_SIZE) & MWAIT_CSTATE_MASK) + 1;
+
+	eax = eax + (choose_substate)(cstate);
+
+	local_irq_disable();
+
+	if (!(lapic_timer_reliable_states & (1 << (cstate))))
+		clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_ENTER, &cpu);
+
+	kt_before = ktime_get_real();
+
+	stop_critical_timings();
+#ifndef MODULE
+	trace_power_start(POWER_CSTATE, (eax >> 4) + 1);
+#endif
+	if (!need_resched()) {
+
+		__monitor((void *)&current_thread_info()->flags, 0, 0);
+		smp_mb();
+		if (!need_resched())
+			__mwait(eax, ecx);
+	}
+
+	start_critical_timings();
+
+	kt_after = ktime_get_real();
+	usec_delta = ktime_to_us(ktime_sub(kt_after, kt_before));
+
+	local_irq_enable();
+
+	if (!(lapic_timer_reliable_states & (1 << (cstate))))
+		clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_EXIT, &cpu);
+
+	return usec_delta;
+}
+
+/*
+ * intel_idle_probe()
+ */
+static int intel_idle_probe(void)
+{
+	unsigned int eax, ebx, ecx, edx;
+
+	if (max_cstate == 0) {
+		pr_debug(PREFIX "disabled\n");
+		return -EPERM;
+	}
+
+	if (boot_cpu_data.x86_vendor != X86_VENDOR_INTEL)
+		return -ENODEV;
+
+	if (!boot_cpu_has(X86_FEATURE_MWAIT))
+		return -ENODEV;
+
+	if (boot_cpu_data.cpuid_level < CPUID_MWAIT_LEAF)
+		return -ENODEV;
+
+	cpuid(CPUID_MWAIT_LEAF, &eax, &ebx, &ecx, &edx);
+
+	if (!(ecx & CPUID5_ECX_EXTENSIONS_SUPPORTED) ||
+		!(ecx & CPUID5_ECX_INTERRUPT_BREAK))
+			return -ENODEV;
+#ifdef DEBUG
+	if (substates == 0)	/* can over-ride via modparam */
+#endif
+		substates = edx;
+
+	pr_debug(PREFIX "MWAIT substates: 0x%x\n", substates);
+
+	if (boot_cpu_has(X86_FEATURE_ARAT))	/* Always Reliable APIC Timer */
+		lapic_timer_reliable_states = 0xFFFFFFFF;
+
+	if (boot_cpu_data.x86 != 6)	/* family 6 */
+		return -ENODEV;
+
+	switch (boot_cpu_data.x86_model) {
+
+	case 0x1A:	/* Core i7, Xeon 5500 series */
+	case 0x1E:	/* Core i7 and i5 Processor - Lynnfield Jasper Forest */
+	case 0x1F:	/* Core i7 and i5 Processor - Nehalem */
+	case 0x2E:	/* Nehalem-EX Xeon */
+		lapic_timer_reliable_states = (1 << 1);	 /* C1 */
+
+	case 0x25:	/* Westmere */
+	case 0x2C:	/* Westmere */
+		cpuidle_state_table = nehalem_cstates;
+		choose_substate = choose_tunable_substate;
+		break;
+
+	case 0x1C:	/* 28 - Atom Processor */
+		lapic_timer_reliable_states = (1 << 2) | (1 << 1); /* C2, C1 */
+		cpuidle_state_table = atom_cstates;
+		choose_substate = choose_zero_substate;
+		break;
+#ifdef FUTURE_USE
+	case 0x17:	/* 23 - Core 2 Duo */
+		lapic_timer_reliable_states = (1 << 2) | (1 << 1); /* C2, C1 */
+#endif
+
+	default:
+		pr_debug(PREFIX "does not run on family %d model %d\n",
+			boot_cpu_data.x86, boot_cpu_data.x86_model);
+		return -ENODEV;
+	}
+
+	pr_debug(PREFIX "v" INTEL_IDLE_VERSION
+		" model 0x%X\n", boot_cpu_data.x86_model);
+
+	pr_debug(PREFIX "lapic_timer_reliable_states 0x%x\n",
+		lapic_timer_reliable_states);
+	return 0;
+}
+
+/*
+ * intel_idle_cpuidle_devices_uninit()
+ * unregister, free cpuidle_devices
+ */
+static void intel_idle_cpuidle_devices_uninit(void)
+{
+	int i;
+	struct cpuidle_device *dev;
+
+	for_each_online_cpu(i) {
+		dev = per_cpu_ptr(intel_idle_cpuidle_devices, i);
+		cpuidle_unregister_device(dev);
+	}
+
+	free_percpu(intel_idle_cpuidle_devices);
+	return;
+}
+/*
+ * intel_idle_cpuidle_devices_init()
+ * allocate, initialize, register cpuidle_devices
+ */
+static int intel_idle_cpuidle_devices_init(void)
+{
+	int i, cstate;
+	struct cpuidle_device *dev;
+
+	intel_idle_cpuidle_devices = alloc_percpu(struct cpuidle_device);
+	if (intel_idle_cpuidle_devices == NULL)
+		return -ENOMEM;
+
+	for_each_online_cpu(i) {
+		dev = per_cpu_ptr(intel_idle_cpuidle_devices, i);
+
+		dev->state_count = 1;
+
+		for (cstate = 1; cstate < MWAIT_MAX_NUM_CSTATES; ++cstate) {
+			int num_substates;
+
+			if (cstate > max_cstate) {
+				printk(PREFIX "max_cstate %d reached\n",
+					max_cstate);
+				break;
+			}
+
+			/* does the state exist in CPUID.MWAIT? */
+			num_substates = (substates >> ((cstate) * 4))
+						& MWAIT_SUBSTATE_MASK;
+			if (num_substates == 0)
+				continue;
+			/* is the state not enabled? */
+			if (cpuidle_state_table[cstate].enter == NULL) {
+				/* does the driver not know about the state? */
+				if (*cpuidle_state_table[cstate].name == '\0')
+					pr_debug(PREFIX "unaware of model 0x%x"
+						" MWAIT %d please"
+						" contact [e-mail]",
+					boot_cpu_data.x86_model, cstate);
+				continue;
+			}
+
+			if ((cstate > 2) &&
+				!boot_cpu_has(X86_FEATURE_NONSTOP_TSC))
+				mark_tsc_unstable("TSC halts in idle"
+					" states deeper than C2");
+
+			dev->states[dev->state_count] =	/* structure copy */
+				cpuidle_state_table[cstate];
+
+			dev->state_count += 1;
+		}
+
+		dev->cpu = i;
+		if (cpuidle_register_device(dev)) {
+			pr_debug(PREFIX "cpuidle_register_device %d failed!\n",
+				 i);
+			intel_idle_cpuidle_devices_uninit();
+			return -EIO;
+		}
+	}
+
+	return 0;
+}
+
+
+static int __init intel_idle_init(void)
+{
+	int retval;
+
+	retval = intel_idle_probe();
+	if (retval)
+		return retval;
+
+	retval = cpuidle_register_driver(&intel_idle_driver);
+	if (retval) {
+		printk(KERN_DEBUG PREFIX "intel_idle yielding to %s",
+			cpuidle_get_driver()->name);
+		return retval;
+	}
+
+	retval = intel_idle_cpuidle_devices_init();
+	if (retval) {
+		cpuidle_unregister_driver(&intel_idle_driver);
+		return retval;
+	}
+
+	return 0;
+}
+
+static void __exit intel_idle_exit(void)
+{
+	intel_idle_cpuidle_devices_uninit();
+	cpuidle_unregister_driver(&intel_idle_driver);
+
+	return;
+}
+
+module_init(intel_idle_init);
+module_exit(intel_idle_exit);
+
+module_param(power_policy, int, 0644);
+module_param(max_cstate, int, 0444);
+#ifdef DEBUG
+module_param(substates, int, 0444);
+#endif
+
+MODULE_AUTHOR("Len Brown <[e-mail]>");
+MODULE_DESCRIPTION("Cpuidle driver for Intel Hardware v" INTEL_IDLE_VERSION);
+MODULE_LICENSE("GPL");