Power management and ACPI updates for 3.11-rc1

- Hotplug changes allowing device hot-removal operations to fail
   gracefully (instead of crashing the kernel) if they cannot be
   carried out completely.  From Rafael J Wysocki and Toshi Kani.
 
 - Freezer update from Colin Cross and Mandeep Singh Baines targeted
   at making the freezing of tasks a bit less heavy weight operation.
 
 - cpufreq resume fix from Srivatsa S Bhat for a regression introduced
   during the 3.10 cycle causing some cpufreq sysfs attributes to
   return wrong values to user space after resume.
 
 - New freqdomain_cpus sysfs attribute for the acpi-cpufreq driver to
   provide information previously available via related_cpus from
   Lan Tianyu.
 
 - cpufreq fixes and cleanups from Viresh Kumar, Jacob Shin,
   Heiko Stübner, Xiaoguang Chen, Ezequiel Garcia, Arnd Bergmann, and
   Tang Yuantian.
 
 - Fix for an ACPICA regression causing suspend/resume issues to
   appear on some systems introduced during the 3.4 development cycle
   from Lv Zheng.
 
 - ACPICA fixes and cleanups from Bob Moore, Tomasz Nowicki, Lv Zheng,
   Chao Guan, and Zhang Rui.
 
 - New cupidle driver for Xilinx Zynq processors from Michal Simek.
 
 - cpuidle fixes and cleanups from Daniel Lezcano.
 
 - Changes to make suspend/resume work correctly in Xen guests from
   Konrad Rzeszutek Wilk.
 
 - ACPI device power management fixes and cleanups from Fengguang Wu
   and Rafael J Wysocki.
 
 - ACPI documentation updates from Lv Zheng, Aaron Lu and Hanjun Guo.
 
 - Fix for the IA-64 issue that was the reason for reverting commit
   9f29ab1 and updates of the ACPI scan code from Rafael J Wysocki.
 
 - Mechanism for adding CMOS RTC address space handlers from Lan Tianyu
   (to allow some EC-related breakage to be fixed on some systems).
 
 - Spec-compliant implementation of acpi_os_get_timer() from
   Mika Westerberg.
 
 - Modification of do_acpi_find_child() to execute _STA in order to
   to avoid situations in which a pointer to a disabled device object
   is returned instead of an enabled one with the same _ADR value.
   From Jeff Wu.
 
 - Intel BayTrail PCH (Platform Controller Hub) support for the ACPI
   Intel Low-Power Subsystems (LPSS) driver and modificaions of that
   driver to work around a couple of known BIOS issues from
   Mika Westerberg and Heikki Krogerus.
 
 - EC driver fix from Vasiliy Kulikov to make it use get_user() and
   put_user() instead of dereferencing user space pointers blindly.
 
 - Assorted ACPI code cleanups from Bjorn Helgaas, Nicholas Mazzuca and
   Toshi Kani.
 
 - Modification of the "runtime idle" helper routine to take the return
   values of the callbacks executed by it into account and to call
   rpm_suspend() if they return 0, which allows some code bloat
   reduction to be done, from Rafael J Wysocki and Alan Stern.
 
 - New trace points for PM QoS from Sahara <[email protected]>.
 
 - PM QoS documentation update from Lan Tianyu.
 
 - Assorted core PM code cleanups and changes from Bernie Thompson,
   Bjorn Helgaas, Julius Werner, and Shuah Khan.
 
 - New devfreq driver for the Exynos5-bus device from Abhilash Kesavan.
 
 - Minor devfreq cleanups, fixes and MAINTAINERS update from
   MyungJoo Ham, Abhilash Kesavan, Paul Bolle, Rajagopal Venkat, and
   Wei Yongjun.
 
 - OMAP Adaptive Voltage Scaling (AVS) SmartReflex voltage control
   driver updates from Andrii Tseglytskyi and Nishanth Menon.
 
 /
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Merge tag 'pm+acpi-3.11-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm

Pull power management and ACPI updates from Rafael Wysocki:
 "This time the total number of ACPI commits is slightly greater than
  the number of cpufreq commits, but Viresh Kumar (who works on cpufreq)
  remains the most active patch submitter.

  To me, the most significant change is the addition of offline/online
  device operations to the driver core (with the Greg's blessing) and
  the related modifications of the ACPI core hotplug code.  Next are the
  freezer updates from Colin Cross that should make the freezing of
  tasks a bit less heavy weight.

  We also have a couple of regression fixes, a number of fixes for
  issues that have not been identified as regressions, two new drivers
  and a bunch of cleanups all over.

  Highlights:

   - Hotplug changes to support graceful hot-removal failures.

     It sometimes is necessary to fail device hot-removal operations
     gracefully if they cannot be carried out completely.  For example,
     if memory from a memory module being hot-removed has been allocated
     for the kernel's own use and cannot be moved elsewhere, it's
     desirable to fail the hot-removal operation in a graceful way
     rather than to crash the kernel, but currenty a success or a kernel
     crash are the only possible outcomes of an attempted memory
     hot-removal.  Needless to say, that is not a very attractive
     alternative and it had to be addressed.

     However, in order to make it work for memory, I first had to make
     it work for CPUs and for this purpose I needed to modify the ACPI
     processor driver.  It's been split into two parts, a resident one
     handling the low-level initialization/cleanup and a modular one
     playing the actual driver's role (but it binds to the CPU system
     device objects rather than to the ACPI device objects representing
     processors).  That's been sort of like a live brain surgery on a
     patient who's riding a bike.

     So this is a little scary, but since we found and fixed a couple of
     regressions it caused to happen during the early linux-next testing
     (a month ago), nobody has complained.

     As a bonus we remove some duplicated ACPI hotplug code, because the
     ACPI-based CPU hotplug is now going to use the common ACPI hotplug
     code.

   - Lighter weight freezing of tasks.

     These changes from Colin Cross and Mandeep Singh Baines are
     targeted at making the freezing of tasks a bit less heavy weight
     operation.  They reduce the number of tasks woken up every time
     during the freezing, by using the observation that the freezer
     simply doesn't need to wake up some of them and wait for them all
     to call refrigerator().  The time needed for the freezer to decide
     to report a failure is reduced too.

     Also reintroduced is the check causing a lockdep warining to
     trigger when try_to_freeze() is called with locks held (which is
     generally unsafe and shouldn't happen).

   - cpufreq updates

     First off, a commit from Srivatsa S Bhat fixes a resume regression
     introduced during the 3.10 cycle causing some cpufreq sysfs
     attributes to return wrong values to user space after resume.  The
     fix is kind of fresh, but also it's pretty obvious once Srivatsa
     has identified the root cause.

     Second, we have a new freqdomain_cpus sysfs attribute for the
     acpi-cpufreq driver to provide information previously available via
     related_cpus.  From Lan Tianyu.

     Finally, we fix a number of issues, mostly related to the
     CPUFREQ_POSTCHANGE notifier and cpufreq Kconfig options and clean
     up some code.  The majority of changes from Viresh Kumar with bits
     from Jacob Shin, Heiko Stübner, Xiaoguang Chen, Ezequiel Garcia,
     Arnd Bergmann, and Tang Yuantian.

   - ACPICA update

     A usual bunch of updates from the ACPICA upstream.

     During the 3.4 cycle we introduced support for ACPI 5 extended
     sleep registers, but they are only supposed to be used if the
     HW-reduced mode bit is set in the FADT flags and the code attempted
     to use them without checking that bit.  That caused suspend/resume
     regressions to happen on some systems.  Fix from Lv Zheng causes
     those registers to be used only if the HW-reduced mode bit is set.

     Apart from this some other ACPICA bugs are fixed and code cleanups
     are made by Bob Moore, Tomasz Nowicki, Lv Zheng, Chao Guan, and
     Zhang Rui.

   - cpuidle updates

     New driver for Xilinx Zynq processors is added by Michal Simek.

     Multidriver support simplification, addition of some missing
     kerneldoc comments and Kconfig-related fixes come from Daniel
     Lezcano.

   - ACPI power management updates

     Changes to make suspend/resume work correctly in Xen guests from
     Konrad Rzeszutek Wilk, sparse warning fix from Fengguang Wu and
     cleanups and fixes of the ACPI device power state selection
     routine.

   - ACPI documentation updates

     Some previously missing pieces of ACPI documentation are added by
     Lv Zheng and Aaron Lu (hopefully, that will help people to
     uderstand how the ACPI subsystem works) and one outdated doc is
     updated by Hanjun Guo.

   - Assorted ACPI updates

     We finally nailed down the IA-64 issue that was the reason for
     reverting commit 9f29ab11dd ("ACPI / scan: do not match drivers
     against objects having scan handlers"), so we can fix it and move
     the ACPI scan handler check added to the ACPI video driver back to
     the core.

     A mechanism for adding CMOS RTC address space handlers is
     introduced by Lan Tianyu to allow some EC-related breakage to be
     fixed on some systems.

     A spec-compliant implementation of acpi_os_get_timer() is added by
     Mika Westerberg.

     The evaluation of _STA is added to do_acpi_find_child() to avoid
     situations in which a pointer to a disabled device object is
     returned instead of an enabled one with the same _ADR value.  From
     Jeff Wu.

     Intel BayTrail PCH (Platform Controller Hub) support is added to
     the ACPI driver for Intel Low-Power Subsystems (LPSS) and that
     driver is modified to work around a couple of known BIOS issues.
     Changes from Mika Westerberg and Heikki Krogerus.

     The EC driver is fixed by Vasiliy Kulikov to use get_user() and
     put_user() instead of dereferencing user space pointers blindly.

     Code cleanups are made by Bjorn Helgaas, Nicholas Mazzuca and Toshi
     Kani.

   - Assorted power management updates

     The "runtime idle" helper routine is changed to take the return
     values of the callbacks executed by it into account and to call
     rpm_suspend() if they return 0, which allows us to reduce the
     overall code bloat a bit (by dropping some code that's not
     necessary any more after that modification).

     The runtime PM documentation is updated by Alan Stern (to reflect
     the "runtime idle" behavior change).

     New trace points for PM QoS are added by Sahara
     (<[email protected]>).

     PM QoS documentation is updated by Lan Tianyu.

     Code cleanups are made and minor issues are addressed by Bernie
     Thompson, Bjorn Helgaas, Julius Werner, and Shuah Khan.

   - devfreq updates

     New driver for the Exynos5-bus device from Abhilash Kesavan.

     Minor cleanups, fixes and MAINTAINERS update from MyungJoo Ham,
     Abhilash Kesavan, Paul Bolle, Rajagopal Venkat, and Wei Yongjun.

   - OMAP power management updates

     Adaptive Voltage Scaling (AVS) SmartReflex voltage control driver
     updates from Andrii Tseglytskyi and Nishanth Menon."

* tag 'pm+acpi-3.11-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm: (162 commits)
  cpufreq: Fix cpufreq regression after suspend/resume
  ACPI / PM: Fix possible NULL pointer deref in acpi_pm_device_sleep_state()
  PM / Sleep: Warn about system time after resume with pm_trace
  cpufreq: don't leave stale policy pointer in cdbs->cur_policy
  acpi-cpufreq: Add new sysfs attribute freqdomain_cpus
  cpufreq: make sure frequency transitions are serialized
  ACPI: implement acpi_os_get_timer() according the spec
  ACPI / EC: Add HP Folio 13 to ec_dmi_table in order to skip DSDT scan
  ACPI: Add CMOS RTC Operation Region handler support
  ACPI / processor: Drop unused variable from processor_perflib.c
  cpufreq: tegra: call CPUFREQ_POSTCHANGE notfier in error cases
  cpufreq: s3c64xx: call CPUFREQ_POSTCHANGE notfier in error cases
  cpufreq: omap: call CPUFREQ_POSTCHANGE notfier in error cases
  cpufreq: imx6q: call CPUFREQ_POSTCHANGE notfier in error cases
  cpufreq: exynos: call CPUFREQ_POSTCHANGE notfier in error cases
  cpufreq: dbx500: call CPUFREQ_POSTCHANGE notfier in error cases
  cpufreq: davinci: call CPUFREQ_POSTCHANGE notfier in error cases
  cpufreq: arm-big-little: call CPUFREQ_POSTCHANGE notfier in error cases
  cpufreq: powernow-k8: call CPUFREQ_POSTCHANGE notfier in error cases
  cpufreq: pcc: call CPUFREQ_POSTCHANGE notfier in error cases
  ...

drivers/cpuidle/Kconfig

@@ -1,7 +1,9 @@
 
-config CPU_IDLE
+menuconfig CPU_IDLE
 	bool "CPU idle PM support"
 	default y if ACPI || PPC_PSERIES
+	select CPU_IDLE_GOV_LADDER if (!NO_HZ && !NO_HZ_IDLE)
+	select CPU_IDLE_GOV_MENU if (NO_HZ || NO_HZ_IDLE)
 	help
 	  CPU idle is a generic framework for supporting software-controlled
 	  idle processor power management.  It includes modular cross-platform
@@ -9,9 +11,10 @@ config CPU_IDLE
 
 	  If you're using an ACPI-enabled platform, you should say Y here.
 
+if CPU_IDLE
+
 config CPU_IDLE_MULTIPLE_DRIVERS
         bool "Support multiple cpuidle drivers"
-        depends on CPU_IDLE
         default n
         help
          Allows the cpuidle framework to use different drivers for each CPU.
@@ -19,20 +22,13 @@ config CPU_IDLE_MULTIPLE_DRIVERS
          states. If unsure say N.
 
 config CPU_IDLE_GOV_LADDER
-	bool
-	depends on CPU_IDLE
+	bool "Ladder governor (for periodic timer tick)"
 	default y
 
 config CPU_IDLE_GOV_MENU
-	bool
-	depends on CPU_IDLE && NO_HZ
+	bool "Menu governor (for tickless system)"
 	default y
 
-config ARCH_NEEDS_CPU_IDLE_COUPLED
-	def_bool n
-
-if CPU_IDLE
-
 config CPU_IDLE_CALXEDA
 	bool "CPU Idle Driver for Calxeda processors"
 	depends on ARCH_HIGHBANK
@@ -40,4 +36,13 @@ config CPU_IDLE_CALXEDA
 	help
 	  Select this to enable cpuidle on Calxeda processors.
 
+config CPU_IDLE_ZYNQ
+	bool "CPU Idle Driver for Xilinx Zynq processors"
+	depends on ARCH_ZYNQ
+	help
+	  Select this to enable cpuidle on Xilinx Zynq processors.
+
 endif
+
+config ARCH_NEEDS_CPU_IDLE_COUPLED
+	def_bool n

drivers/cpuidle/Makefile

@@ -7,3 +7,4 @@ obj-$(CONFIG_ARCH_NEEDS_CPU_IDLE_COUPLED) += coupled.o
 
 obj-$(CONFIG_CPU_IDLE_CALXEDA) += cpuidle-calxeda.o
 obj-$(CONFIG_ARCH_KIRKWOOD) += cpuidle-kirkwood.o
+obj-$(CONFIG_CPU_IDLE_ZYNQ) += cpuidle-zynq.o

drivers/cpuidle/cpuidle-zynq.c

@@ -0,0 +1,83 @@
+/*
+ * Copyright (C) 2012-2013 Xilinx
+ *
+ * CPU idle support for Xilinx Zynq
+ *
+ * based on arch/arm/mach-at91/cpuidle.c
+ *
+ * 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, see <http://www.gnu.org/licenses/>.
+ *
+ * The cpu idle uses wait-for-interrupt and RAM self refresh in order
+ * to implement two idle states -
+ * #1 wait-for-interrupt
+ * #2 wait-for-interrupt and RAM self refresh
+ *
+ * Maintainer: Michal Simek <michal.simek@xilinx.com>
+ */
+
+#include <linux/init.h>
+#include <linux/cpu_pm.h>
+#include <linux/cpuidle.h>
+#include <linux/of.h>
+#include <asm/proc-fns.h>
+#include <asm/cpuidle.h>
+
+#define ZYNQ_MAX_STATES		2
+
+/* Actual code that puts the SoC in different idle states */
+static int zynq_enter_idle(struct cpuidle_device *dev,
+			   struct cpuidle_driver *drv, int index)
+{
+	/* Devices must be stopped here */
+	cpu_pm_enter();
+
+	/* Add code for DDR self refresh start */
+	cpu_do_idle();
+
+	/* Add code for DDR self refresh stop */
+	cpu_pm_exit();
+
+	return index;
+}
+
+static struct cpuidle_driver zynq_idle_driver = {
+	.name = "zynq_idle",
+	.owner = THIS_MODULE,
+	.states = {
+		ARM_CPUIDLE_WFI_STATE,
+		{
+			.enter			= zynq_enter_idle,
+			.exit_latency		= 10,
+			.target_residency	= 10000,
+			.flags			= CPUIDLE_FLAG_TIME_VALID |
+						  CPUIDLE_FLAG_TIMER_STOP,
+			.name			= "RAM_SR",
+			.desc			= "WFI and RAM Self Refresh",
+		},
+	},
+	.safe_state_index = 0,
+	.state_count = ZYNQ_MAX_STATES,
+};
+
+/* Initialize CPU idle by registering the idle states */
+static int __init zynq_cpuidle_init(void)
+{
+	if (!of_machine_is_compatible("xlnx,zynq-7000"))
+		return -ENODEV;
+
+	pr_info("Xilinx Zynq CpuIdle Driver started\n");
+
+	return cpuidle_register(&zynq_idle_driver, NULL);
+}
+
+device_initcall(zynq_cpuidle_init);

drivers/cpuidle/cpuidle.c

@@ -466,7 +466,7 @@ void cpuidle_unregister(struct cpuidle_driver *drv)
 	int cpu;
 	struct cpuidle_device *device;
 
-	for_each_possible_cpu(cpu) {
+	for_each_cpu(cpu, drv->cpumask) {
 		device = &per_cpu(cpuidle_dev, cpu);
 		cpuidle_unregister_device(device);
 	}
@@ -498,7 +498,7 @@ int cpuidle_register(struct cpuidle_driver *drv,
 		return ret;
 	}
 
-	for_each_possible_cpu(cpu) {
+	for_each_cpu(cpu, drv->cpumask) {
 		device = &per_cpu(cpuidle_dev, cpu);
 		device->cpu = cpu;
 

drivers/cpuidle/driver.c

@@ -18,182 +18,249 @@
 
 DEFINE_SPINLOCK(cpuidle_driver_lock);
 
-static void __cpuidle_set_cpu_driver(struct cpuidle_driver *drv, int cpu);
-static struct cpuidle_driver * __cpuidle_get_cpu_driver(int cpu);
-
-static void cpuidle_setup_broadcast_timer(void *arg)
-{
-	int cpu = smp_processor_id();
-	clockevents_notify((long)(arg), &cpu);
-}
-
-static void __cpuidle_driver_init(struct cpuidle_driver *drv, int cpu)
-{
-	int i;
-
-	drv->refcnt = 0;
-
-	for (i = drv->state_count - 1; i >= 0 ; i--) {
-
-		if (!(drv->states[i].flags & CPUIDLE_FLAG_TIMER_STOP))
-			continue;
-
-		drv->bctimer = 1;
-		on_each_cpu_mask(get_cpu_mask(cpu), cpuidle_setup_broadcast_timer,
-				 (void *)CLOCK_EVT_NOTIFY_BROADCAST_ON, 1);
-		break;
-	}
-}
-
-static int __cpuidle_register_driver(struct cpuidle_driver *drv, int cpu)
-{
-	if (!drv || !drv->state_count)
-		return -EINVAL;
-
-	if (cpuidle_disabled())
-		return -ENODEV;
-
-	if (__cpuidle_get_cpu_driver(cpu))
-		return -EBUSY;
-
-	__cpuidle_driver_init(drv, cpu);
-
-	__cpuidle_set_cpu_driver(drv, cpu);
-
-	return 0;
-}
-
-static void __cpuidle_unregister_driver(struct cpuidle_driver *drv, int cpu)
-{
-	if (drv != __cpuidle_get_cpu_driver(cpu))
-		return;
-
-	if (!WARN_ON(drv->refcnt > 0))
-		__cpuidle_set_cpu_driver(NULL, cpu);
-
-	if (drv->bctimer) {
-		drv->bctimer = 0;
-		on_each_cpu_mask(get_cpu_mask(cpu), cpuidle_setup_broadcast_timer,
-				 (void *)CLOCK_EVT_NOTIFY_BROADCAST_OFF, 1);
-	}
-}
-
 #ifdef CONFIG_CPU_IDLE_MULTIPLE_DRIVERS
 
 static DEFINE_PER_CPU(struct cpuidle_driver *, cpuidle_drivers);
 
-static void __cpuidle_set_cpu_driver(struct cpuidle_driver *drv, int cpu)
-{
-	per_cpu(cpuidle_drivers, cpu) = drv;
-}
-
+/**
+ * __cpuidle_get_cpu_driver - return the cpuidle driver tied to a CPU.
+ * @cpu: the CPU handled by the driver
+ *
+ * Returns a pointer to struct cpuidle_driver or NULL if no driver has been
+ * registered for @cpu.
+ */
 static struct cpuidle_driver *__cpuidle_get_cpu_driver(int cpu)
 {
 	return per_cpu(cpuidle_drivers, cpu);
 }
 
-static void __cpuidle_unregister_all_cpu_driver(struct cpuidle_driver *drv)
+/**
+ * __cpuidle_unset_driver - unset per CPU driver variables.
+ * @drv: a valid pointer to a struct cpuidle_driver
+ *
+ * For each CPU in the driver's CPU mask, unset the registered driver per CPU
+ * variable. If @drv is different from the registered driver, the corresponding
+ * variable is not cleared.
+ */
+static inline void __cpuidle_unset_driver(struct cpuidle_driver *drv)
 {
 	int cpu;
-	for_each_present_cpu(cpu)
-		__cpuidle_unregister_driver(drv, cpu);
+
+	for_each_cpu(cpu, drv->cpumask) {
+
+		if (drv != __cpuidle_get_cpu_driver(cpu))
+			continue;
+
+		per_cpu(cpuidle_drivers, cpu) = NULL;
+	}
 }
 
-static int __cpuidle_register_all_cpu_driver(struct cpuidle_driver *drv)
+/**
+ * __cpuidle_set_driver - set per CPU driver variables the the given driver.
+ * @drv: a valid pointer to a struct cpuidle_driver
+ *
+ * For each CPU in the driver's cpumask, unset the registered driver per CPU
+ * to @drv.
+ *
+ * Returns 0 on success, -EBUSY if the CPUs have driver(s) already.
+ */
+static inline int __cpuidle_set_driver(struct cpuidle_driver *drv)
 {
-	int ret = 0;
-	int i, cpu;
+	int cpu;
 
-	for_each_present_cpu(cpu) {
-		ret = __cpuidle_register_driver(drv, cpu);
-		if (ret)
-			break;
-	}
+	for_each_cpu(cpu, drv->cpumask) {
 
-	if (ret)
-		for_each_present_cpu(i) {
-			if (i == cpu)
-				break;
-			__cpuidle_unregister_driver(drv, i);
+		if (__cpuidle_get_cpu_driver(cpu)) {
+			__cpuidle_unset_driver(drv);
+			return -EBUSY;
 		}
 
+		per_cpu(cpuidle_drivers, cpu) = drv;
+	}
 
-	return ret;
+	return 0;
 }
 
-int cpuidle_register_cpu_driver(struct cpuidle_driver *drv, int cpu)
-{
-	int ret;
-
-	spin_lock(&cpuidle_driver_lock);
-	ret = __cpuidle_register_driver(drv, cpu);
-	spin_unlock(&cpuidle_driver_lock);
-
-	return ret;
-}
-
-void cpuidle_unregister_cpu_driver(struct cpuidle_driver *drv, int cpu)
-{
-	spin_lock(&cpuidle_driver_lock);
-	__cpuidle_unregister_driver(drv, cpu);
-	spin_unlock(&cpuidle_driver_lock);
-}
-
-/**
- * cpuidle_register_driver - registers a driver
- * @drv: the driver
- */
-int cpuidle_register_driver(struct cpuidle_driver *drv)
-{
-	int ret;
-
-	spin_lock(&cpuidle_driver_lock);
-	ret = __cpuidle_register_all_cpu_driver(drv);
-	spin_unlock(&cpuidle_driver_lock);
-
-	return ret;
-}
-EXPORT_SYMBOL_GPL(cpuidle_register_driver);
-
-/**
- * cpuidle_unregister_driver - unregisters a driver
- * @drv: the driver
- */
-void cpuidle_unregister_driver(struct cpuidle_driver *drv)
-{
-	spin_lock(&cpuidle_driver_lock);
-	__cpuidle_unregister_all_cpu_driver(drv);
-	spin_unlock(&cpuidle_driver_lock);
-}
-EXPORT_SYMBOL_GPL(cpuidle_unregister_driver);
-
 #else
 
 static struct cpuidle_driver *cpuidle_curr_driver;
 
-static inline void __cpuidle_set_cpu_driver(struct cpuidle_driver *drv, int cpu)
-{
-	cpuidle_curr_driver = drv;
-}
-
+/**
+ * __cpuidle_get_cpu_driver - return the global cpuidle driver pointer.
+ * @cpu: ignored without the multiple driver support
+ *
+ * Return a pointer to a struct cpuidle_driver object or NULL if no driver was
+ * previously registered.
+ */
 static inline struct cpuidle_driver *__cpuidle_get_cpu_driver(int cpu)
 {
 	return cpuidle_curr_driver;
 }
 
+/**
+ * __cpuidle_set_driver - assign the global cpuidle driver variable.
+ * @drv: pointer to a struct cpuidle_driver object
+ *
+ * Returns 0 on success, -EBUSY if the driver is already registered.
+ */
+static inline int __cpuidle_set_driver(struct cpuidle_driver *drv)
+{
+	if (cpuidle_curr_driver)
+		return -EBUSY;
+
+	cpuidle_curr_driver = drv;
+
+	return 0;
+}
+
+/**
+ * __cpuidle_unset_driver - unset the global cpuidle driver variable.
+ * @drv: a pointer to a struct cpuidle_driver
+ *
+ * Reset the global cpuidle variable to NULL.  If @drv does not match the
+ * registered driver, do nothing.
+ */
+static inline void __cpuidle_unset_driver(struct cpuidle_driver *drv)
+{
+	if (drv == cpuidle_curr_driver)
+		cpuidle_curr_driver = NULL;
+}
+
+#endif
+
+/**
+ * cpuidle_setup_broadcast_timer - enable/disable the broadcast timer
+ * @arg: a void pointer used to match the SMP cross call API
+ *
+ * @arg is used as a value of type 'long' with on of the two values:
+ * - CLOCK_EVT_NOTIFY_BROADCAST_ON
+ * - CLOCK_EVT_NOTIFY_BROADCAST_OFF
+ *
+ * Set the broadcast timer notification for the current CPU.  This function
+ * is executed per CPU by an SMP cross call.  It not supposed to be called
+ * directly.
+ */
+static void cpuidle_setup_broadcast_timer(void *arg)
+{
+	int cpu = smp_processor_id();
+	clockevents_notify((long)(arg), &cpu);
+}
+
+/**
+ * __cpuidle_driver_init - initialize the driver's internal data
+ * @drv: a valid pointer to a struct cpuidle_driver
+ *
+ * Returns 0 on success, a negative error code otherwise.
+ */
+static int __cpuidle_driver_init(struct cpuidle_driver *drv)
+{
+	int i;
+
+	drv->refcnt = 0;
+
+	/*
+	 * Use all possible CPUs as the default, because if the kernel boots
+	 * with some CPUs offline and then we online one of them, the CPU
+	 * notifier has to know which driver to assign.
+	 */
+	if (!drv->cpumask)
+		drv->cpumask = (struct cpumask *)cpu_possible_mask;
+
+	/*
+	 * Look for the timer stop flag in the different states, so that we know
+	 * if the broadcast timer has to be set up.  The loop is in the reverse
+	 * order, because usually on of the the deeper states has this flag set.
+	 */
+	for (i = drv->state_count - 1; i >= 0 ; i--) {
+
+		if (!(drv->states[i].flags & CPUIDLE_FLAG_TIMER_STOP))
+			continue;
+
+		drv->bctimer = 1;
+		break;
+	}
+
+	return 0;
+}
+
+/**
+ * __cpuidle_register_driver: register the driver
+ * @drv: a valid pointer to a struct cpuidle_driver
+ *
+ * Do some sanity checks, initialize the driver, assign the driver to the
+ * global cpuidle driver variable(s) and set up the broadcast timer if the
+ * cpuidle driver has some states that shut down the local timer.
+ *
+ * Returns 0 on success, a negative error code otherwise:
+ *  * -EINVAL if the driver pointer is NULL or no idle states are available
+ *  * -ENODEV if the cpuidle framework is disabled
+ *  * -EBUSY if the driver is already assigned to the global variable(s)
+ */
+static int __cpuidle_register_driver(struct cpuidle_driver *drv)
+{
+	int ret;
+
+	if (!drv || !drv->state_count)
+		return -EINVAL;
+
+	if (cpuidle_disabled())
+		return -ENODEV;
+
+	ret = __cpuidle_driver_init(drv);
+	if (ret)
+		return ret;
+
+	ret = __cpuidle_set_driver(drv);
+	if (ret)
+		return ret;
+
+	if (drv->bctimer)
+		on_each_cpu_mask(drv->cpumask, cpuidle_setup_broadcast_timer,
+				 (void *)CLOCK_EVT_NOTIFY_BROADCAST_ON, 1);
+
+	return 0;
+}
+
+/**
+ * __cpuidle_unregister_driver - unregister the driver
+ * @drv: a valid pointer to a struct cpuidle_driver
+ *
+ * Check if the driver is no longer in use, reset the global cpuidle driver
+ * variable(s) and disable the timer broadcast notification mechanism if it was
+ * in use.
+ *
+ */
+static void __cpuidle_unregister_driver(struct cpuidle_driver *drv)
+{
+	if (WARN_ON(drv->refcnt > 0))
+		return;
+
+	if (drv->bctimer) {
+		drv->bctimer = 0;
+		on_each_cpu_mask(drv->cpumask, cpuidle_setup_broadcast_timer,
+				 (void *)CLOCK_EVT_NOTIFY_BROADCAST_OFF, 1);
+	}
+
+	__cpuidle_unset_driver(drv);
+}
+
 /**
  * cpuidle_register_driver - registers a driver
- * @drv: the driver
+ * @drv: a pointer to a valid struct cpuidle_driver
+ *
+ * Register the driver under a lock to prevent concurrent attempts to
+ * [un]register the driver from occuring at the same time.
+ *
+ * Returns 0 on success, a negative error code (returned by
+ * __cpuidle_register_driver()) otherwise.
  */
 int cpuidle_register_driver(struct cpuidle_driver *drv)
 {
-	int ret, cpu;
+	int ret;
 
-	cpu = get_cpu();
 	spin_lock(&cpuidle_driver_lock);
-	ret = __cpuidle_register_driver(drv, cpu);
+	ret = __cpuidle_register_driver(drv);
 	spin_unlock(&cpuidle_driver_lock);
-	put_cpu();
 
 	return ret;
 }
@@ -201,23 +268,24 @@ EXPORT_SYMBOL_GPL(cpuidle_register_driver);
 
 /**
  * cpuidle_unregister_driver - unregisters a driver
- * @drv: the driver
+ * @drv: a pointer to a valid struct cpuidle_driver
+ *
+ * Unregisters the cpuidle driver under a lock to prevent concurrent attempts
+ * to [un]register the driver from occuring at the same time.  @drv has to
+ * match the currently registered driver.
  */
 void cpuidle_unregister_driver(struct cpuidle_driver *drv)
 {
-	int cpu;
-
-	cpu = get_cpu();
 	spin_lock(&cpuidle_driver_lock);
-	__cpuidle_unregister_driver(drv, cpu);
+	__cpuidle_unregister_driver(drv);
 	spin_unlock(&cpuidle_driver_lock);
-	put_cpu();
 }
 EXPORT_SYMBOL_GPL(cpuidle_unregister_driver);
-#endif
 
 /**
- * cpuidle_get_driver - return the current driver
+ * cpuidle_get_driver - return the driver tied to the current CPU.
+ *
+ * Returns a struct cpuidle_driver pointer, or NULL if no driver is registered.
  */
 struct cpuidle_driver *cpuidle_get_driver(void)
 {
@@ -233,7 +301,11 @@ struct cpuidle_driver *cpuidle_get_driver(void)
 EXPORT_SYMBOL_GPL(cpuidle_get_driver);
 
 /**
- * cpuidle_get_cpu_driver - return the driver tied with a cpu
+ * cpuidle_get_cpu_driver - return the driver registered for a CPU.
+ * @dev: a valid pointer to a struct cpuidle_device
+ *
+ * Returns a struct cpuidle_driver pointer, or NULL if no driver is registered
+ * for the CPU associated with @dev.
  */
 struct cpuidle_driver *cpuidle_get_cpu_driver(struct cpuidle_device *dev)
 {
@@ -244,6 +316,14 @@ struct cpuidle_driver *cpuidle_get_cpu_driver(struct cpuidle_device *dev)
 }
 EXPORT_SYMBOL_GPL(cpuidle_get_cpu_driver);
 
+/**
+ * cpuidle_driver_ref - get a reference to the driver.
+ *
+ * Increment the reference counter of the cpuidle driver associated with
+ * the current CPU.
+ *
+ * Returns a pointer to the driver, or NULL if the current CPU has no driver.
+ */
 struct cpuidle_driver *cpuidle_driver_ref(void)
 {
 	struct cpuidle_driver *drv;
@@ -257,6 +337,12 @@ struct cpuidle_driver *cpuidle_driver_ref(void)
 	return drv;
 }
 
+/**
+ * cpuidle_driver_unref - puts down the refcount for the driver
+ *
+ * Decrement the reference counter of the cpuidle driver associated with
+ * the current CPU.
+ */
 void cpuidle_driver_unref(void)
 {
 	struct cpuidle_driver *drv = cpuidle_get_driver();