[PATCH v4 5/6] drivers: cpuidle: CPU idle ARM64 driver

This patch implements a generic CPU idle driver for ARM64 machines.

It relies on the DT idle states infrastructure to initialize idle
states count and respective parameters. Current code assumes the driver
is managing idle states on all possible CPUs but can be easily
generalized to support heterogenous systems and build cpumasks at
runtime using MIDRs or DT cpu nodes compatible properties.

Suspend back-ends (eg PSCI) must register a suspend initializer with
the CPU idle driver so that the suspend backend call can be detected,
and the driver code can call the back-end infrastructure to complete the
suspend backend initialization.

Idle state index 0 is always initialized as a simple wfi state, ie always
considered present and functional on all ARM64 platforms.

Signed-off-by: Lorenzo Pieralisi <redacted>
---
 drivers/cpuidle/Kconfig         |   5 ++
 drivers/cpuidle/Kconfig.arm64   |  13 ++++
 drivers/cpuidle/Makefile        |   4 +
 drivers/cpuidle/cpuidle-arm64.c | 168 ++++++++++++++++++++++++++++++++++++++++
 4 files changed, 190 insertions(+)
 create mode 100644 drivers/cpuidle/Kconfig.arm64
 create mode 100644 drivers/cpuidle/cpuidle-arm64.c

diff --git a/drivers/cpuidle/Kconfig b/drivers/cpuidle/Kconfig
index 760ce20..360c086 100644
--- a/drivers/cpuidle/Kconfig
+++ b/drivers/cpuidle/Kconfig

@@ -44,6 +44,11 @@ depends on ARM
 source "drivers/cpuidle/Kconfig.arm"
 endmenu
 
+menu "ARM64 CPU Idle Drivers"
+depends on ARM64
+source "drivers/cpuidle/Kconfig.arm64"
+endmenu
+
 menu "MIPS CPU Idle Drivers"
 depends on MIPS
 source "drivers/cpuidle/Kconfig.mips"

diff --git a/drivers/cpuidle/Kconfig.arm64 b/drivers/cpuidle/Kconfig.arm64
new file mode 100644
index 0000000..b83612c
--- /dev/null
+++ b/drivers/cpuidle/Kconfig.arm64

@@ -0,0 +1,13 @@
+#
+# ARM64 CPU Idle drivers
+#
+
+config ARM64_CPUIDLE
+	bool "Generic ARM64 CPU idle Driver"
+	select OF_IDLE_STATES
+	help
+	  Select this to enable generic cpuidle driver for ARM v8.
+	  It provides a generic idle driver whose idle states are configured
+	  at run-time through DT nodes. The CPUidle suspend backend is
+	  initialized by the device tree parsing code on matching the entry
+	  method to the respective CPU operations.

diff --git a/drivers/cpuidle/Makefile b/drivers/cpuidle/Makefile
index d5ebf4b..e496242 100644
--- a/drivers/cpuidle/Makefile
+++ b/drivers/cpuidle/Makefile

@@ -23,6 +23,10 @@ obj-$(CONFIG_ARM_EXYNOS_CPUIDLE)        += cpuidle-exynos.o
 obj-$(CONFIG_MIPS_CPS_CPUIDLE)		+= cpuidle-cps.o
 
 ###############################################################################
+# ARM64 drivers
+obj-$(CONFIG_ARM64_CPUIDLE)		+= cpuidle-arm64.o
+
+###############################################################################
 # POWERPC drivers
 obj-$(CONFIG_PSERIES_CPUIDLE)		+= cpuidle-pseries.o
 obj-$(CONFIG_POWERNV_CPUIDLE)		+= cpuidle-powernv.o

diff --git a/drivers/cpuidle/cpuidle-arm64.c b/drivers/cpuidle/cpuidle-arm64.c
new file mode 100644
index 0000000..4c932f8
--- /dev/null
+++ b/drivers/cpuidle/cpuidle-arm64.c

@@ -0,0 +1,168 @@
+/*
+ * ARM64 generic CPU idle driver.
+ *
+ * Copyright (C) 2014 ARM Ltd.
+ * Author: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
+ *
+ * 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.
+ */
+
+#define pr_fmt(fmt) "CPUidle arm64: " fmt
+
+#include <linux/cpuidle.h>
+#include <linux/cpumask.h>
+#include <linux/cpu_pm.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/of.h>
+
+#include <asm/psci.h>
+#include <asm/suspend.h>
+
+#include "of_idle_states.h"
+
+typedef int (*suspend_init_fn)(struct cpuidle_driver *,
+			       struct device_node *[]);
+
+struct cpu_suspend_ops {
+	const char *id;
+	suspend_init_fn init_fn;
+};
+
+static const struct cpu_suspend_ops suspend_operations[] __initconst = {
+	{"arm,psci", psci_dt_register_idle_states},
+	{}
+};
+
+static __init const struct cpu_suspend_ops *get_suspend_ops(const char *str)
+{
+	int i;
+
+	if (!str)
+		return NULL;
+
+	for (i = 0; suspend_operations[i].id; i++)
+		if (!strcmp(suspend_operations[i].id, str))
+			return &suspend_operations[i];
+
+	return NULL;
+}
+
+/*
+ * arm_enter_idle_state - Programs CPU to enter the specified state
+ *
+ * dev: cpuidle device
+ * drv: cpuidle driver
+ * idx: state index
+ *
+ * Called from the CPUidle framework to program the device to the
+ * specified target state selected by the governor.
+ */
+static int arm_enter_idle_state(struct cpuidle_device *dev,
+				struct cpuidle_driver *drv, int idx)
+{
+	int ret;
+
+	if (!idx) {
+		cpu_do_idle();
+		return idx;
+	}
+
+	cpu_pm_enter();
+	/*
+	 * Pass idle state index to cpu_suspend which in turn will call
+	 * the CPU ops suspend protocol with idle index as a parameter.
+	 *
+	 * Some states would not require context to be saved and flushed
+	 * to DRAM, so calling cpu_suspend would not be stricly necessary.
+	 * When power domains specifications for ARM CPUs are finalized then
+	 * this code can be optimized to prevent saving registers if not
+	 * needed.
+	 */
+	ret = cpu_suspend(idx);
+
+	cpu_pm_exit();
+
+	return ret ? -1 : idx;
+}
+
+struct cpuidle_driver arm64_idle_driver = {
+	.name = "arm64_idle",
+	.owner = THIS_MODULE,
+};
+
+static struct device_node *state_nodes[CPUIDLE_STATE_MAX] __initdata;
+
+/*
+ * arm64_idle_init
+ *
+ * Registers the arm64 specific cpuidle driver with the cpuidle
+ * framework. It relies on core code to parse the idle states
+ * and initialize them using driver data structures accordingly.
+ */
+static int __init arm64_idle_init(void)
+{
+	int i, ret;
+	const char *entry_method;
+	struct device_node *idle_states_node;
+	const struct cpu_suspend_ops *suspend_init;
+	struct cpuidle_driver *drv = &arm64_idle_driver;
+
+	idle_states_node = of_find_node_by_path("/cpus/idle-states");
+	if (!idle_states_node)
+		return -ENOENT;
+
+	if (of_property_read_string(idle_states_node, "entry-method",
+				    &entry_method)) {
+		pr_warn(" * %s missing entry-method property\n",
+			    idle_states_node->full_name);
+		of_node_put(idle_states_node);
+		ret = -EOPNOTSUPP;
+		goto put_node;
+	}
+
+	suspend_init = get_suspend_ops(entry_method);
+	if (!suspend_init) {
+		pr_warn("Missing suspend initializer\n");
+		ret = -EOPNOTSUPP;
+		goto put_node;
+	}
+
+	/*
+	 * State at index 0 is standby wfi and considered standard
+	 * on all ARM platforms. If in some platforms simple wfi
+	 * can't be used as "state 0", DT bindings must be implemented
+	 * to work around this issue and allow installing a special
+	 * handler for idle state index 0.
+	 */
+	drv->states[0].exit_latency = 1;
+	drv->states[0].target_residency = 1;
+	drv->states[0].flags = CPUIDLE_FLAG_TIME_VALID;
+	strncpy(drv->states[0].name, "ARM WFI", CPUIDLE_NAME_LEN);
+	strncpy(drv->states[0].desc, "ARM WFI", CPUIDLE_DESC_LEN);
+
+	drv->cpumask = (struct cpumask *) cpu_possible_mask;
+	/*
+	 * Start at index 1, request idle state nodes to be filled
+	 */
+	ret = of_init_idle_driver(drv, state_nodes, 1, true);
+	if (ret)
+		goto put_node;
+
+	if (suspend_init->init_fn(drv, state_nodes)) {
+		ret = -EOPNOTSUPP;
+		goto put_node;
+	}
+
+	for (i = 0; i < drv->state_count; i++)
+		drv->states[i].enter = arm_enter_idle_state;
+
+	ret = cpuidle_register(drv, NULL);
+
+put_node:
+	of_node_put(idle_states_node);
+	return ret;
+}
+device_initcall(arm64_idle_init);

-- 
1.8.4

On 06/11/2014 06:18 PM, Lorenzo Pieralisi wrote:

Is it sure cpu_suspend will return always 0 on success ?

+}
+
+struct cpuidle_driver arm64_idle_driver = {
+	.name = "arm64_idle",
+	.owner = THIS_MODULE,
+};
+
+static struct device_node *state_nodes[CPUIDLE_STATE_MAX] __initdata;
+
+/*
+ * arm64_idle_init
+ *
+ * Registers the arm64 specific cpuidle driver with the cpuidle
+ * framework. It relies on core code to parse the idle states
+ * and initialize them using driver data structures accordingly.
+ */
+static int __init arm64_idle_init(void)
+{
+	int i, ret;
+	const char *entry_method;
+	struct device_node *idle_states_node;
+	const struct cpu_suspend_ops *suspend_init;
+	struct cpuidle_driver *drv = &arm64_idle_driver;
+
+	idle_states_node = of_find_node_by_path("/cpus/idle-states");
+	if (!idle_states_node)
+		return -ENOENT;
+
+	if (of_property_read_string(idle_states_node, "entry-method",
+				    &entry_method)) {
+		pr_warn(" * %s missing entry-method property\n",
+			    idle_states_node->full_name);
+		of_node_put(idle_states_node);
+		ret = -EOPNOTSUPP;
+		goto put_node;
+	}
+
+	suspend_init = get_suspend_ops(entry_method);
+	if (!suspend_init) {
+		pr_warn("Missing suspend initializer\n");
+		ret = -EOPNOTSUPP;
+		goto put_node;
+	}
+
+	/*
+	 * State at index 0 is standby wfi and considered standard
+	 * on all ARM platforms. If in some platforms simple wfi
+	 * can't be used as "state 0", DT bindings must be implemented
+	 * to work around this issue and allow installing a special
+	 * handler for idle state index 0.
+	 */
+	drv->states[0].exit_latency = 1;
+	drv->states[0].target_residency = 1;
+	drv->states[0].flags = CPUIDLE_FLAG_TIME_VALID;
+	strncpy(drv->states[0].name, "ARM WFI", CPUIDLE_NAME_LEN);
+	strncpy(drv->states[0].desc, "ARM WFI", CPUIDLE_DESC_LEN);

Please do not copy the state name and desc strings, they will be 
converted to 'const char *'.

+	drv->cpumask = (struct cpumask *) cpu_possible_mask;
+	/*
+	 * Start at index 1, request idle state nodes to be filled
+	 */
+	ret = of_init_idle_driver(drv, state_nodes, 1, true);
+	if (ret)
+		goto put_node;
+
+	if (suspend_init->init_fn(drv, state_nodes)) {
+		ret = -EOPNOTSUPP;
+		goto put_node;
+	}
+
+	for (i = 0; i < drv->state_count; i++)
+		drv->states[i].enter = arm_enter_idle_state;

May be s/arm/arm64/ ?

+
+	ret = cpuidle_register(drv, NULL);
+
+put_node:
+	of_node_put(idle_states_node);
+	return ret;
+}
+device_initcall(arm64_idle_init);

-- 
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On Wed, Jun 11, 2014 at 11:18 AM, Lorenzo Pieralisi
[off-list ref] wrote:

This patch implements a generic CPU idle driver for ARM64 machines.

I fail to see anything arm64 specific here. The idle states binding is
for both arm32 and arm64, right? If not, please make it for both.
Otherwise, I'm okay with the binding for the most part. I need to take
another pass at it though.

Rob

On Thu, Jun 19, 2014 at 04:02:18AM +0100, Rob Herring wrote:

On Wed, Jun 11, 2014 at 11:18 AM, Lorenzo Pieralisi
[off-list ref] wrote:

quoted

This patch implements a generic CPU idle driver for ARM64 machines.

I fail to see anything arm64 specific here. The idle states binding is
for both arm32 and arm64, right? If not, please make it for both.
Otherwise, I'm okay with the binding for the most part. I need to take
another pass at it though.

cpu_suspend prototypes differ and that has implications, in particular
related to how to initialize the cpu_suspend back-end. I think that with some
effort we might have a single common driver for arm32/64, I have to check if
it is worth the additional ifdeffery that is likely to be needed.

Certainly the DT bindings are generic for arm32/arm64 and we are trying
to make code using them generic too, the best we can.

I will post a v5 soon, please let me know if that's ok to go when time
comes.

Thank you,
Lorenzo

Rob

quoted

It relies on the DT idle states infrastructure to initialize idle
states count and respective parameters. Current code assumes the driver
is managing idle states on all possible CPUs but can be easily
generalized to support heterogenous systems and build cpumasks at
runtime using MIDRs or DT cpu nodes compatible properties.

Suspend back-ends (eg PSCI) must register a suspend initializer with
the CPU idle driver so that the suspend backend call can be detected,
and the driver code can call the back-end infrastructure to complete the
suspend backend initialization.

Idle state index 0 is always initialized as a simple wfi state, ie always
considered present and functional on all ARM64 platforms.

Signed-off-by: Lorenzo Pieralisi <redacted>
---
 drivers/cpuidle/Kconfig         |   5 ++
 drivers/cpuidle/Kconfig.arm64   |  13 ++++
 drivers/cpuidle/Makefile        |   4 +
 drivers/cpuidle/cpuidle-arm64.c | 168 ++++++++++++++++++++++++++++++++++++++++
 4 files changed, 190 insertions(+)
 create mode 100644 drivers/cpuidle/Kconfig.arm64
 create mode 100644 drivers/cpuidle/cpuidle-arm64.c

diff --git a/drivers/cpuidle/Kconfig b/drivers/cpuidle/Kconfig
index 760ce20..360c086 100644
--- a/drivers/cpuidle/Kconfig
+++ b/drivers/cpuidle/Kconfig

@@ -44,6 +44,11 @@ depends on ARM
 source "drivers/cpuidle/Kconfig.arm"
 endmenu

+menu "ARM64 CPU Idle Drivers"
+depends on ARM64
+source "drivers/cpuidle/Kconfig.arm64"
+endmenu
+
 menu "MIPS CPU Idle Drivers"
 depends on MIPS
 source "drivers/cpuidle/Kconfig.mips"

diff --git a/drivers/cpuidle/Kconfig.arm64 b/drivers/cpuidle/Kconfig.arm64
new file mode 100644
index 0000000..b83612c
--- /dev/null
+++ b/drivers/cpuidle/Kconfig.arm64

@@ -0,0 +1,13 @@
+#
+# ARM64 CPU Idle drivers
+#
+
+config ARM64_CPUIDLE
+       bool "Generic ARM64 CPU idle Driver"
+       select OF_IDLE_STATES
+       help
+         Select this to enable generic cpuidle driver for ARM v8.
+         It provides a generic idle driver whose idle states are configured
+         at run-time through DT nodes. The CPUidle suspend backend is
+         initialized by the device tree parsing code on matching the entry
+         method to the respective CPU operations.

diff --git a/drivers/cpuidle/Makefile b/drivers/cpuidle/Makefile
index d5ebf4b..e496242 100644
--- a/drivers/cpuidle/Makefile
+++ b/drivers/cpuidle/Makefile

@@ -23,6 +23,10 @@ obj-$(CONFIG_ARM_EXYNOS_CPUIDLE)        += cpuidle-exynos.o
 obj-$(CONFIG_MIPS_CPS_CPUIDLE)         += cpuidle-cps.o

 ###############################################################################
+# ARM64 drivers
+obj-$(CONFIG_ARM64_CPUIDLE)            += cpuidle-arm64.o
+
+###############################################################################
 # POWERPC drivers
 obj-$(CONFIG_PSERIES_CPUIDLE)          += cpuidle-pseries.o
 obj-$(CONFIG_POWERNV_CPUIDLE)          += cpuidle-powernv.o

diff --git a/drivers/cpuidle/cpuidle-arm64.c b/drivers/cpuidle/cpuidle-arm64.c
new file mode 100644
index 0000000..4c932f8
--- /dev/null
+++ b/drivers/cpuidle/cpuidle-arm64.c

@@ -0,0 +1,168 @@
+/*
+ * ARM64 generic CPU idle driver.
+ *
+ * Copyright (C) 2014 ARM Ltd.
+ * Author: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
+ *
+ * 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.
+ */
+
+#define pr_fmt(fmt) "CPUidle arm64: " fmt
+
+#include <linux/cpuidle.h>
+#include <linux/cpumask.h>
+#include <linux/cpu_pm.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/of.h>
+
+#include <asm/psci.h>
+#include <asm/suspend.h>
+
+#include "of_idle_states.h"
+
+typedef int (*suspend_init_fn)(struct cpuidle_driver *,
+                              struct device_node *[]);
+
+struct cpu_suspend_ops {
+       const char *id;
+       suspend_init_fn init_fn;
+};
+
+static const struct cpu_suspend_ops suspend_operations[] __initconst = {
+       {"arm,psci", psci_dt_register_idle_states},
+       {}
+};
+
+static __init const struct cpu_suspend_ops *get_suspend_ops(const char *str)
+{
+       int i;
+
+       if (!str)
+               return NULL;
+
+       for (i = 0; suspend_operations[i].id; i++)
+               if (!strcmp(suspend_operations[i].id, str))
+                       return &suspend_operations[i];
+
+       return NULL;
+}
+
+/*
+ * arm_enter_idle_state - Programs CPU to enter the specified state
+ *
+ * dev: cpuidle device
+ * drv: cpuidle driver
+ * idx: state index
+ *
+ * Called from the CPUidle framework to program the device to the
+ * specified target state selected by the governor.
+ */
+static int arm_enter_idle_state(struct cpuidle_device *dev,
+                               struct cpuidle_driver *drv, int idx)
+{
+       int ret;
+
+       if (!idx) {
+               cpu_do_idle();
+               return idx;
+       }
+
+       cpu_pm_enter();
+       /*
+        * Pass idle state index to cpu_suspend which in turn will call
+        * the CPU ops suspend protocol with idle index as a parameter.
+        *
+        * Some states would not require context to be saved and flushed
+        * to DRAM, so calling cpu_suspend would not be stricly necessary.
+        * When power domains specifications for ARM CPUs are finalized then
+        * this code can be optimized to prevent saving registers if not
+        * needed.
+        */
+       ret = cpu_suspend(idx);
+
+       cpu_pm_exit();
+
+       return ret ? -1 : idx;
+}
+
+struct cpuidle_driver arm64_idle_driver = {
+       .name = "arm64_idle",
+       .owner = THIS_MODULE,
+};
+
+static struct device_node *state_nodes[CPUIDLE_STATE_MAX] __initdata;
+
+/*
+ * arm64_idle_init
+ *
+ * Registers the arm64 specific cpuidle driver with the cpuidle
+ * framework. It relies on core code to parse the idle states
+ * and initialize them using driver data structures accordingly.
+ */
+static int __init arm64_idle_init(void)
+{
+       int i, ret;
+       const char *entry_method;
+       struct device_node *idle_states_node;
+       const struct cpu_suspend_ops *suspend_init;
+       struct cpuidle_driver *drv = &arm64_idle_driver;
+
+       idle_states_node = of_find_node_by_path("/cpus/idle-states");
+       if (!idle_states_node)
+               return -ENOENT;
+
+       if (of_property_read_string(idle_states_node, "entry-method",
+                                   &entry_method)) {
+               pr_warn(" * %s missing entry-method property\n",
+                           idle_states_node->full_name);
+               of_node_put(idle_states_node);
+               ret = -EOPNOTSUPP;
+               goto put_node;
+       }
+
+       suspend_init = get_suspend_ops(entry_method);
+       if (!suspend_init) {
+               pr_warn("Missing suspend initializer\n");
+               ret = -EOPNOTSUPP;
+               goto put_node;
+       }
+
+       /*
+        * State at index 0 is standby wfi and considered standard
+        * on all ARM platforms. If in some platforms simple wfi
+        * can't be used as "state 0", DT bindings must be implemented
+        * to work around this issue and allow installing a special
+        * handler for idle state index 0.
+        */
+       drv->states[0].exit_latency = 1;
+       drv->states[0].target_residency = 1;
+       drv->states[0].flags = CPUIDLE_FLAG_TIME_VALID;
+       strncpy(drv->states[0].name, "ARM WFI", CPUIDLE_NAME_LEN);
+       strncpy(drv->states[0].desc, "ARM WFI", CPUIDLE_DESC_LEN);
+
+       drv->cpumask = (struct cpumask *) cpu_possible_mask;
+       /*
+        * Start at index 1, request idle state nodes to be filled
+        */
+       ret = of_init_idle_driver(drv, state_nodes, 1, true);
+       if (ret)
+               goto put_node;
+
+       if (suspend_init->init_fn(drv, state_nodes)) {
+               ret = -EOPNOTSUPP;
+               goto put_node;
+       }
+
+       for (i = 0; i < drv->state_count; i++)
+               drv->states[i].enter = arm_enter_idle_state;
+
+       ret = cpuidle_register(drv, NULL);
+
+put_node:
+       of_node_put(idle_states_node);
+       return ret;
+}
+device_initcall(arm64_idle_init);
--

1.8.4


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On Wed, Jun 18, 2014 at 10:34:06PM +0100, Daniel Lezcano wrote:

[...]

quoted

+/*
+ * arm_enter_idle_state - Programs CPU to enter the specified state
+ *
+ * dev: cpuidle device
+ * drv: cpuidle driver
+ * idx: state index
+ *
+ * Called from the CPUidle framework to program the device to the
+ * specified target state selected by the governor.
+ */
+static int arm_enter_idle_state(struct cpuidle_device *dev,
+				struct cpuidle_driver *drv, int idx)
+{
+	int ret;
+
+	if (!idx) {
+		cpu_do_idle();
+		return idx;
+	}
+
+	cpu_pm_enter();
+	/*
+	 * Pass idle state index to cpu_suspend which in turn will call
+	 * the CPU ops suspend protocol with idle index as a parameter.
+	 *
+	 * Some states would not require context to be saved and flushed
+	 * to DRAM, so calling cpu_suspend would not be stricly necessary.
+	 * When power domains specifications for ARM CPUs are finalized then
+	 * this code can be optimized to prevent saving registers if not
+	 * needed.
+	 */
+	ret = cpu_suspend(idx);
+
+	cpu_pm_exit();
+
+	return ret ? -1 : idx;

Is it sure cpu_suspend will return always 0 on success ?

Yes. Now, we have to define "success". On ARM32/64 success means
returning through cpu_resume, which can also happen if a CPU is soft
rebooted following a power down failure. It depends on how the
cpu_suspend back-end behaves on power down failure, if it just returns
or it soft-reboots the CPU. It is an implementation detail, do not think
it is a major problem at the moment.

quoted

+}
+
+struct cpuidle_driver arm64_idle_driver = {
+	.name = "arm64_idle",
+	.owner = THIS_MODULE,
+};
+
+static struct device_node *state_nodes[CPUIDLE_STATE_MAX] __initdata;
+
+/*
+ * arm64_idle_init
+ *
+ * Registers the arm64 specific cpuidle driver with the cpuidle
+ * framework. It relies on core code to parse the idle states
+ * and initialize them using driver data structures accordingly.
+ */
+static int __init arm64_idle_init(void)
+{
+	int i, ret;
+	const char *entry_method;
+	struct device_node *idle_states_node;
+	const struct cpu_suspend_ops *suspend_init;
+	struct cpuidle_driver *drv = &arm64_idle_driver;
+
+	idle_states_node = of_find_node_by_path("/cpus/idle-states");
+	if (!idle_states_node)
+		return -ENOENT;
+
+	if (of_property_read_string(idle_states_node, "entry-method",
+				    &entry_method)) {
+		pr_warn(" * %s missing entry-method property\n",
+			    idle_states_node->full_name);
+		of_node_put(idle_states_node);
+		ret = -EOPNOTSUPP;
+		goto put_node;
+	}
+
+	suspend_init = get_suspend_ops(entry_method);
+	if (!suspend_init) {
+		pr_warn("Missing suspend initializer\n");
+		ret = -EOPNOTSUPP;
+		goto put_node;
+	}
+
+	/*
+	 * State at index 0 is standby wfi and considered standard
+	 * on all ARM platforms. If in some platforms simple wfi
+	 * can't be used as "state 0", DT bindings must be implemented
+	 * to work around this issue and allow installing a special
+	 * handler for idle state index 0.
+	 */
+	drv->states[0].exit_latency = 1;
+	drv->states[0].target_residency = 1;
+	drv->states[0].flags = CPUIDLE_FLAG_TIME_VALID;
+	strncpy(drv->states[0].name, "ARM WFI", CPUIDLE_NAME_LEN);
+	strncpy(drv->states[0].desc, "ARM WFI", CPUIDLE_DESC_LEN);

Please do not copy the state name and desc strings, they will be 
converted to 'const char *'.

Ok, I need to sync this code with those changes though.

quoted

+	drv->cpumask = (struct cpumask *) cpu_possible_mask;
+	/*
+	 * Start at index 1, request idle state nodes to be filled
+	 */
+	ret = of_init_idle_driver(drv, state_nodes, 1, true);
+	if (ret)
+		goto put_node;
+
+	if (suspend_init->init_fn(drv, state_nodes)) {
+		ret = -EOPNOTSUPP;
+		goto put_node;
+	}
+
+	for (i = 0; i < drv->state_count; i++)
+		drv->states[i].enter = arm_enter_idle_state;

May be s/arm/arm64/ ?

Well, yes, unless we go for a common arm/arm64 driver (see Rob's email),
with related pros and cons.

Let's make a decision on this asap, I do not think we are that far from
a common solution.

Thanks a lot,
Lorenzo