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* [RFC v3 00/12] PM: SoC idle support using PM domains
@ 2016-03-01 21:15 Lina Iyer
  2016-03-01 21:15 ` [BUG FIX] PM / cpu_domains: Check for NULL callbacks Lina Iyer
                   ` (12 more replies)
  0 siblings, 13 replies; 23+ messages in thread
From: Lina Iyer @ 2016-03-01 21:15 UTC (permalink / raw)
  To: ulf.hansson, khilman, rjw, linux-pm, linux-arm-kernel
  Cc: geert, k.kozlowski, msivasub, agross, sboyd, linux-arm-msm,
	lorenzo.pieralisi, ahaslam, mtitinger, Lina Iyer

Hi all,

Changes since RFC v2 [6] -
- Bug fix for NULL callbacks
- Address review comments from Stephen

Changes since RFC v1 [1] -
- genpd lock abstraction using fn ptrs. Sparse is happier.
- Removed restriction that IRQ-safe domains can only have IRQ safe parents [3]
- changes in the way CPU domains are initialized, starting from CPU now
	* cpu-map node dependency removed
	* platform driver initiate CPU PM domain setup
- smaller patchset excluding genpd multiple level changes
	* they were submitted to ML earlier [2]
- cpuidle runtime PM and hotplug changes
- PSCI changes to detect if the f/w supports OSI
- updated documentation
- this new cover description

This series allows CPU common hardware blocks to enter idle state, when the
CPUs are in idle. A lightweight but important power saving in a battery powered
device is power savings when the device is not suspended. While being active,
the CPUs can save power by entering low power states with the help of cpuidle
framework, but the hardware supporting these CPU still remain active. This is
an effort in reducing power on these h/w block around the CPU during cpuidle.

Every CPU decides for itself the deepest low power mode possible and enters
that state to be more power effecient. This is unlike coupled states, where
CPUs have to wait until the last of the CPU is ready to enter the deepest idle.
The last of the CPU that enters idle decides for the domain, the best idle
state the domain may enter. This is also a higher level than what MCPM solves.
In newer SoC's the coherency and other race conditions coming out of warm reset
are handled in the firmware. This patchset helps Linux make the right power
decision for other h/w blocks that are dependent on the CPUs.

The idea is that CPU hierarchy (represented in DT) is modelled as regular
devices attached to their PM domains, which in turn may be attached to its
parent domain. When cpuidle puts the CPU to sleep, runtime PM for the CPU
device is notified, which suspends the CPU device. This triggers a reduction in
genpd domain usage count. When the last device in a domain suspends, the domain
is powered off as part of the same call. Similarly, the domain resumes before
the first CPU device resumes from idle. To achieve this the following changes
are needed -
	- genpd to support multiple idle states (more than just on/off)
	- genpd should support suspend/resume from IRQ safe context
	- CPU devices set up for runtime PM, as IRQ safe devices
	- cpuidle calls runtime PM ops when idling
	- the genpd power downs calling into a gov to determine the deepest idle state 
	- genpd ->power_on()/->power_off() callbacks to be handled by the platform

Patches from Axel [2] allow genpd to define multiple idle states and choose the
best idle state from them.

These patches build up on top of that -

- Patches [1, 2] - Genpd changes
Sets up Generic PM domains to be called from cpuidle. Genpd uses mutexes for
synchronization. This has to be changed to spinlocks for domains that may be
called from IRQ safe contexts.

- Patch [3] - CPU PM domains
Parses DT and sets up PM domains for CPUs and builds up the hierarchy of
domains and devices. These are bunch of helper functions.

- Patch [4] - ARM cpuidle driver
Enable ARM cpuidle driver to call runtime PM. Even though this has been done
for ARM, there is nothing architecture specific about this. Currently, all idle
states other than ARM clock gating calls into runtime PM. This could also be
state specific i.e call into runtime PM only after a certain state. The changes
may be made part of cpuidle framework, but needs discussion.

- Patches [5, 6, 7] - PM domain governor for CPUs
Introduces a new genpd governor that looks into the per-CPU tick device to
identify the next CPU wakeup and determine the available sleep time for the
domain. This along with QoS is used to determine the best idle state for the
domain. A domains' wake up is determined by the first CPU in that domain to
wake up. A coherency level domain's (parent of a domain containing CPU devices)
wake up is determined by the first CPU amongst all the CPUs to wake up.
Identifying the CPUs and their wakeups are the part of these patches.

- Patches [9, 10] - ARM64 PSCI platform driver
ARM64 PSCI v1.0 specific. PSCI OS initiated mode supports powering off CPU
clusters (caches etc, by configuring separate power controllers). These patches
enable Linux to determine if the f/w supports this mode and if so, uses CPU PM
domain helper functions to create PM domains and handles the power_on/power_off
callbacks. The resulting cluster state is passed as an argument to the f/w
along with the CPU state.

- Patches [11, 12] - DTS changes for MSM8916
QCOM 410c Dragonboard/96Board specific. Enables CPUidle and cluster idle for
this SoC. A compatible f/w (in the works) is needed for this support.

Testing and results -

This patchset has been tested on a QCOM 410c Dragonboard with a quad ARM v8 A53
CPU and 512KB L2 cache. Though not accurate, I see a ~20 mA drop in current
measured at the battery outside the SoC when the SoC idle is enabled. This
needs to be redone again to get an accurate measurement. I see about ~5 us
increase before entering idle state to determine the last man down and about
~20 us while coming out of idle (in Linux) when the cache is flushed and
powered down.

This was tested on top of 4.5-rc3. My series along with patches from Axel can
be found at [4]. Note that [5] has not been published on the ML, is needed for
this series.

Thanks,
Lina

[1]. http://comments.gmane.org/gmane.linux.ports.arm.msm/16232
[2]. http://permalink.gmane.org/gmane.linux.power-management.general/71387
[3]. http://permalink.gmane.org/gmane.linux.ports.arm.msm/17279
[4]. https://git.linaro.org/people/lina.iyer/linux-next.git/shortlog/refs/heads/genpd-psci-RFC-v3
[5]. https://git.linaro.org/people/lina.iyer/linux-next.git/commit/1dfec82c8c133b0fbcd245d739dade087a1dd1fc
[6]. https://lwn.net/Articles/675674/


Lina Iyer (12):
  PM / Domains: Abstract genpd locking
  PM / Domains: Support IRQ safe PM domains
  PM / cpu_domains: Setup PM domains for CPUs/clusters
  ARM: cpuidle: Add runtime PM support for CPUs
  timer: Export next wake up of a CPU
  PM / cpu_domains: Record CPUs that are part of the domain
  PM / cpu_domains: Add PM Domain governor for CPUs
  Documentation / cpu_domains: Describe CPU PM domains setup and
    governor
  drivers: firmware: psci: Allow OS Initiated suspend mode
  ARM64: psci: Support cluster idle states for OS-Initiated
  ARM64: dts: Add PSCI cpuidle support for MSM8916
  ARM64: dts: Define CPU power domain for MSM8916

 Documentation/power/cpu_domains.txt   |  79 ++++++++
 Documentation/power/devices.txt       |  12 +-
 arch/arm64/boot/dts/qcom/msm8916.dtsi |  49 +++++
 arch/arm64/kernel/psci.c              |  46 ++++-
 drivers/base/power/Makefile           |   1 +
 drivers/base/power/cpu_domains.c      | 365 ++++++++++++++++++++++++++++++++++
 drivers/base/power/domain.c           | 210 +++++++++++++++----
 drivers/cpuidle/cpuidle-arm.c         |  55 +++++
 drivers/firmware/psci.c               |  45 ++++-
 include/linux/cpu_domains.h           |  37 ++++
 include/linux/pm_domain.h             |  14 +-
 include/linux/psci.h                  |   2 +
 include/linux/tick.h                  |  10 +
 include/uapi/linux/psci.h             |   5 +
 kernel/time/tick-sched.c              |  13 ++
 15 files changed, 896 insertions(+), 47 deletions(-)
 create mode 100644 Documentation/power/cpu_domains.txt
 create mode 100644 drivers/base/power/cpu_domains.c
 create mode 100644 include/linux/cpu_domains.h

-- 
2.1.4

^ permalink raw reply	[flat|nested] 23+ messages in thread
* [RFC v2 03/12] PM / cpu_domains: Setup PM domains for CPUs/clusters
@ 2016-02-12 20:50 Lina Iyer
  2016-02-18 17:29 ` [BUG FIX] PM / cpu_domains: Check for NULL callbacks Lina Iyer
  0 siblings, 1 reply; 23+ messages in thread
From: Lina Iyer @ 2016-02-12 20:50 UTC (permalink / raw)
  To: ulf.hansson, khilman, rjw, linux-pm, linux-arm-kernel
  Cc: geert, k.kozlowski, msivasub, agross, sboyd, linux-arm-msm,
	lorenzo.pieralisi, ahaslam, mtitinger, Lina Iyer, Daniel Lezcano

Define and add Generic PM domains (genpd) for CPU clusters. Many new
SoCs group CPUs as clusters. Clusters share common resources like power
rails, caches, VFP, Coresight etc. When all CPUs in the cluster are
idle, these shared resources may also be put in their idle state.

CPUs may be associated with their domain providers in DT. The domains in
turn may be associated with their providers. This is clean way to model
the cluster hierarchy like that of ARM's big.little architecture.

For each CPU in the DT, we identify the domain provider; initialize and
register the PM domain if isn't already registered and attach all the
CPU devices to the domain. Usually, when there are multiple clusters of
CPUs, there is a top level coherency domain that is dependent on these
individual domains. All domains thus created are marked IRQ safe
automatically and therefore may be powered down when the CPUs in the
domain are powered down by cpuidle.

Reading DT, initializing Generic PM domains, attaching CPUs to it
domains are common functionalities across ARM SoCs. Provide a common set
of APIs to setup PM domains for CPU clusters and its parents. The
platform drivers may just call of_setup_cpu_pd() to do a single step
setup of CPU domains.

Cc: Ulf Hansson <ulf.hansson@linaro.org>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Suggested-by: Kevin Hilman <khilman@linaro.org>
Signed-off-by: Lina Iyer <lina.iyer@linaro.org>
---
Changes since RFC v1 -
- Initialize down up, start with CPUs, identify and create domains
- Clean up of the API
- Two simple API for setting up CPU PM domains
- File name change: cpu-pd.[ch] ->cpu_domains.[ch]
- Depends on CONFIG_PM_GENERIC_DOMAINS_OF only
- cpu_pd_ops abstracts generic pm domains
- platform code does not know about genpd object used inside
- simplification and bug fixes

 drivers/base/power/Makefile      |   1 +
 drivers/base/power/cpu_domains.c | 267 +++++++++++++++++++++++++++++++++++++++
 include/linux/cpu_domains.h      |  33 +++++
 3 files changed, 301 insertions(+)
 create mode 100644 drivers/base/power/cpu_domains.c
 create mode 100644 include/linux/cpu_domains.h

diff --git a/drivers/base/power/Makefile b/drivers/base/power/Makefile
index 5998c53..9883e89 100644
--- a/drivers/base/power/Makefile
+++ b/drivers/base/power/Makefile
@@ -3,6 +3,7 @@ obj-$(CONFIG_PM_SLEEP)	+= main.o wakeup.o
 obj-$(CONFIG_PM_TRACE_RTC)	+= trace.o
 obj-$(CONFIG_PM_OPP)	+= opp/
 obj-$(CONFIG_PM_GENERIC_DOMAINS)	+=  domain.o domain_governor.o
+obj-$(CONFIG_PM_GENERIC_DOMAINS_OF)	+= cpu_domains.o
 obj-$(CONFIG_HAVE_CLK)	+= clock_ops.o
 
 ccflags-$(CONFIG_DEBUG_DRIVER) := -DDEBUG
diff --git a/drivers/base/power/cpu_domains.c b/drivers/base/power/cpu_domains.c
new file mode 100644
index 0000000..981592f
--- /dev/null
+++ b/drivers/base/power/cpu_domains.c
@@ -0,0 +1,267 @@
+/*
+ * drivers/base/power/cpu_domains.c - Helper functions to create CPU PM domains.
+ *
+ * Copyright (C) 2016 Linaro Ltd.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/cpu.h>
+#include <linux/cpu_domains.h>
+#include <linux/cpu_pm.h>
+#include <linux/device.h>
+#include <linux/kernel.h>
+#include <linux/list.h>
+#include <linux/of.h>
+#include <linux/pm_domain.h>
+#include <linux/rculist.h>
+#include <linux/rcupdate.h>
+#include <linux/slab.h>
+
+#define CPU_PD_NAME_MAX 36
+
+struct cpu_pm_domain {
+	struct list_head link;
+	struct cpu_pd_ops ops;
+	struct generic_pm_domain *genpd;
+	struct cpu_pm_domain *parent;
+};
+
+/* List of CPU PM domains we care about */
+static LIST_HEAD(of_cpu_pd_list);
+static DEFINE_SPINLOCK(cpu_pd_list_lock);
+
+static inline
+struct cpu_pm_domain *to_cpu_pd(struct generic_pm_domain *d)
+{
+	struct cpu_pm_domain *pd;
+	struct cpu_pm_domain *res = NULL;
+
+	rcu_read_lock();
+	list_for_each_entry_rcu(pd, &of_cpu_pd_list, link)
+		if (pd->genpd == d) {
+			res = pd;
+			break;
+		}
+	rcu_read_unlock();
+
+	return res;
+}
+
+static int cpu_pd_attach_cpu(int cpu)
+{
+	int ret;
+	struct device *cpu_dev;
+
+	cpu_dev = get_cpu_device(cpu);
+	if (!cpu_dev) {
+		pr_warn("%s: Unable to get device for CPU%d\n",
+				__func__, cpu);
+		return -ENODEV;
+	}
+
+	ret = genpd_dev_pm_attach(cpu_dev);
+	if (ret)
+		dev_warn(cpu_dev,
+			"%s: Unable to attach to power-domain: %d\n",
+			__func__, ret);
+	else
+		dev_dbg(cpu_dev, "Attached to domain\n");
+
+	return ret;
+}
+
+static int cpu_pd_power_on(struct generic_pm_domain *genpd)
+{
+	struct cpu_pm_domain *pd = to_cpu_pd(genpd);
+
+	return pd->ops.power_on();
+}
+
+static int cpu_pd_power_off(struct generic_pm_domain *genpd)
+{
+	struct cpu_pm_domain *pd = to_cpu_pd(genpd);
+
+	return pd->ops.power_off(genpd->state_idx,
+			genpd->states[genpd->state_idx].param);
+}
+
+/**
+ * of_init_cpu_pm_domain() - Initialize a CPU PM domain from a device node
+ *
+ * @dn: The domain provider's device node
+ * @ops: The power_on/_off callbacks for the domain
+ *
+ * Returns the generic_pm_domain (genpd) pointer to the domain on success
+ */
+static struct generic_pm_domain *of_init_cpu_pm_domain(struct device_node *dn,
+				const struct cpu_pd_ops *ops)
+{
+	struct cpu_pm_domain *pd = NULL;
+	struct generic_pm_domain *genpd = NULL;
+	int ret = -ENOMEM;
+
+	if (!of_device_is_available(dn))
+		return ERR_PTR(-ENODEV);
+
+	genpd = kzalloc(sizeof(*(genpd)), GFP_KERNEL);
+	if (!genpd)
+		goto fail;
+
+	genpd->name = kstrndup(dn->full_name, CPU_PD_NAME_MAX, GFP_KERNEL);
+	if (!genpd->name)
+		goto fail;
+
+	pd = kzalloc(sizeof(*pd), GFP_KERNEL);
+	if (!pd)
+		goto fail;
+
+	pd->genpd = genpd;
+	pd->genpd->power_off = cpu_pd_power_off;
+	pd->genpd->power_on = cpu_pd_power_on;
+	pd->genpd->flags |= GENPD_FLAG_IRQ_SAFE;
+	pd->ops.power_on = ops->power_on;
+	pd->ops.power_off = ops->power_off;
+
+	INIT_LIST_HEAD_RCU(&pd->link);
+	spin_lock(&cpu_pd_list_lock);
+	list_add_rcu(&pd->link, &of_cpu_pd_list);
+	spin_unlock(&cpu_pd_list_lock);
+
+	/* Register the CPU genpd */
+	pr_debug("adding %s as CPU PM domain.\n", pd->genpd->name);
+	ret = of_pm_genpd_init(dn, pd->genpd, &simple_qos_governor, false);
+	if (ret) {
+		pr_err("Unable to initialize domain %s\n", dn->full_name);
+		goto fail;
+	}
+
+	ret = of_genpd_add_provider_simple(dn, pd->genpd);
+	if (ret)
+		pr_warn("Unable to add genpd %s as provider\n",
+				pd->genpd->name);
+
+	return pd->genpd;
+fail:
+
+	kfree(genpd);
+	kfree(genpd->name);
+	kfree(pd);
+	return ERR_PTR(ret);
+}
+
+static struct generic_pm_domain *of_get_cpu_domain(struct device_node *dn,
+		const struct cpu_pd_ops *ops, int cpu)
+{
+	struct of_phandle_args args;
+	struct generic_pm_domain *genpd, *parent;
+	int ret;
+
+	/* Do we have this domain? If not, create the domain */
+	args.np = dn;
+	args.args_count = 0;
+
+	genpd = of_genpd_get_from_provider(&args);
+	if (!IS_ERR(genpd))
+		goto skip_parent;
+
+	genpd = of_init_cpu_pm_domain(dn, ops);
+	if (IS_ERR(genpd))
+		return genpd;
+
+	/* Is there a domain provider for this domain? */
+	ret = of_parse_phandle_with_args(dn, "power-domains",
+			"#power-domain-cells", 0, &args);
+	of_node_put(dn);
+	if (ret < 0)
+		goto skip_parent;
+
+	/* Find its parent and attach this domain to it, recursively */
+	parent = of_get_cpu_domain(args.np, ops, cpu);
+	if (IS_ERR(parent)) {
+		struct cpu_pm_domain *cpu_pd, *parent_cpu_pd;
+
+		ret = pm_genpd_add_subdomain(genpd, parent);
+		if (ret) {
+			pr_err("%s: Unable to add sub-domain (%s) to parent (%s)\n err: %d",
+					__func__, genpd->name, parent->name,
+					ret);
+			return ERR_PTR(ret);
+		}
+
+		/*
+		 * Reference parent domain for easy access.
+		 * Note: We could be attached to a domain that is not a
+		 * CPU PM domain in that case dont reference the parent.
+		 */
+		cpu_pd = to_cpu_pd(genpd);
+		parent_cpu_pd = to_cpu_pd(parent);
+
+		if (cpu_pd && parent_cpu_pd)
+			cpu_pd->parent = parent_cpu_pd;
+	}
+
+skip_parent:
+	return genpd;
+}
+
+/**
+ * of_setup_cpu_pd_single() - Setup the PM domains for a CPU
+ *
+ * @cpu: The CPU for which the PM domain is to be set up.
+ * @ops: The PM domain suspend/resume ops for the CPU's domain
+ *
+ * If the CPU PM domain exists already, then the CPU is attached to
+ * that CPU PD. If it doesn't, the domain is created, the @ops are
+ * set for power_on/power_off callbacks and then the CPU is attached
+ * to that domain. If the domain was created outside this framework,
+ * then we do not attach the CPU to the domain.
+ */
+int of_setup_cpu_pd_single(int cpu, const struct cpu_pd_ops *ops)
+{
+
+	struct device_node *dn;
+	struct generic_pm_domain *genpd;
+
+	dn = of_get_cpu_node(cpu, NULL);
+	if (!dn)
+		return -ENODEV;
+
+	dn = of_parse_phandle(dn, "power-domains", 0);
+	if (!dn)
+		return -ENODEV;
+	of_node_put(dn);
+
+	/* Find the genpd for this CPU, create if not found */
+	genpd = of_get_cpu_domain(dn, ops, cpu);
+	if (IS_ERR(genpd))
+		return PTR_ERR(genpd);
+
+	return cpu_pd_attach_cpu(cpu);
+}
+EXPORT_SYMBOL(of_setup_cpu_pd_single);
+
+/**
+ * of_setup_cpu_pd() - Setup the PM domains for all CPUs
+ *
+ * @ops: The PM domain suspend/resume ops for all the domains
+ *
+ * Setup the CPU PM domain and attach all possible CPUs to their respective
+ * domains. The domains are created if not already and then attached.
+ */
+int of_setup_cpu_pd(const struct cpu_pd_ops *ops)
+{
+	int cpu;
+	int ret;
+
+	for_each_possible_cpu(cpu) {
+		ret = of_setup_cpu_pd_single(cpu, ops);
+		if (ret)
+			break;
+	}
+
+	return ret;
+}
+EXPORT_SYMBOL(of_setup_cpu_pd);
diff --git a/include/linux/cpu_domains.h b/include/linux/cpu_domains.h
new file mode 100644
index 0000000..bab4846
--- /dev/null
+++ b/include/linux/cpu_domains.h
@@ -0,0 +1,33 @@
+/*
+ * include/linux/cpu_domains.h
+ *
+ * Copyright (C) 2016 Linaro Ltd.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#ifndef __CPU_DOMAINS_H__
+#define __CPU_DOMAINS_H__
+
+struct cpu_pd_ops {
+	int (*power_off)(u32 state_idx, u32 param);
+	int (*power_on)(void);
+};
+
+#ifdef CONFIG_PM_GENERIC_DOMAINS_OF
+int of_setup_cpu_pd_single(int cpu, const struct cpu_pd_ops *ops);
+int of_setup_cpu_pd(const struct cpu_pd_ops *ops);
+#else
+static inline int of_setup_cpu_pd_single(int cpu, const struct cpu_pd_ops *ops)
+{
+	return -ENODEV;
+}
+static inline int of_setup_cpu_pd(const struct cpu_pd_ops *ops)
+{
+	return -ENODEV;
+}
+#endif /* CONFIG_PM_GENERIC_DOMAINS_OF */
+
+#endif /* __CPU_DOMAINS_H__ */
-- 
2.1.4


^ permalink raw reply related	[flat|nested] 23+ messages in thread
end of thread, other threads:[~2016-03-21  3:50 UTC | newest]

Thread overview: 23+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2016-03-01 21:15 [RFC v3 00/12] PM: SoC idle support using PM domains Lina Iyer
2016-03-01 21:15 ` [BUG FIX] PM / cpu_domains: Check for NULL callbacks Lina Iyer
2016-03-01 21:17   ` Lina Iyer
2016-03-01 21:15 ` [RFC v3 01/12] PM / Domains: Abstract genpd locking Lina Iyer
2016-03-04 10:09   ` Ulf Hansson
2016-03-01 21:15 ` [RFC v3 02/12] PM / Domains: Support IRQ safe PM domains Lina Iyer
2016-03-03  0:57   ` Kevin Hilman
2016-03-01 21:15 ` [RFC v3 03/12] PM / cpu_domains: Setup PM domains for CPUs/clusters Lina Iyer
2016-03-03  1:18   ` Kevin Hilman
2016-03-01 21:15 ` [RFC v3 04/12] ARM: cpuidle: Add runtime PM support for CPUs Lina Iyer
2016-03-04 18:03   ` Stephen Boyd
2016-03-01 21:15 ` [RFC v3 05/12] timer: Export next wake up of a CPU Lina Iyer
2016-03-01 21:15 ` [RFC v3 06/12] PM / cpu_domains: Record CPUs that are part of the domain Lina Iyer
2016-03-01 21:15 ` [RFC v3 07/12] PM / cpu_domains: Add PM Domain governor for CPUs Lina Iyer
2016-03-01 21:15 ` [RFC v3 08/12] Documentation / cpu_domains: Describe CPU PM domains setup and governor Lina Iyer
2016-03-01 21:15 ` [RFC v3 09/12] drivers: firmware: psci: Allow OS Initiated suspend mode Lina Iyer
2016-03-01 21:15 ` [RFC v3 10/12] ARM64: psci: Support cluster idle states for OS-Initiated Lina Iyer
2016-03-01 21:15 ` [RFC v3 11/12] ARM64: dts: Add PSCI cpuidle support for MSM8916 Lina Iyer
2016-03-21  3:50   ` Andy Gross
2016-03-01 21:15 ` [RFC v3 12/12] ARM64: dts: Define CPU power domain " Lina Iyer
  -- strict thread matches above, loose matches on Subject: below --
2016-02-12 20:50 [RFC v2 03/12] PM / cpu_domains: Setup PM domains for CPUs/clusters Lina Iyer
2016-02-18 17:29 ` [BUG FIX] PM / cpu_domains: Check for NULL callbacks Lina Iyer
2016-02-18 17:46   ` Rafael J. Wysocki
2016-02-18 22:51     ` Lina Iyer

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