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From:   Vincent Guittot <vincent.guittot@linaro.org>
Date:   Wed, 31 Jan 2018 10:01:21 +0100
Message-ID: <CAKfTPtD-cUYoAJfhtuTr-E1=rttZvWxVv1Qv7b+Si4vSBy0JVg@mail.gmail.com>
Subject: Re: [PATCH 5/8] thermal/drivers/cpu_cooling: Introduce the cpu idle
 cooling driver
To:     Daniel Lezcano <daniel.lezcano@linaro.org>
Cc:     Eduardo Valentin <edubezval@gmail.com>,
        Kevin Wangtao <kevin.wangtao@linaro.org>,
        Leo Yan <leo.yan@linaro.org>,
        Amit Kachhap <amit.kachhap@gmail.com>,
        viresh kumar <viresh.kumar@linaro.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Zhang Rui <rui.zhang@intel.com>,
        Javi Merino <javi.merino@kernel.org>,
        "open list:THERMAL" <linux-pm@vger.kernel.org>
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Sender: linux-kernel-owner@vger.kernel.org
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Hi Daniel,

On 23 January 2018 at 16:34, Daniel Lezcano <daniel.lezcano@linaro.org> wro=
te:
> The cpu idle cooling driver performs synchronized idle injection across a=
ll
> cpus belonging to the same cluster and offers a new method to cool down a=
 SoC.
>
> Each cluster has its own idle cooling device, each core has its own idle
> injection thread, each idle injection thread uses play_idle to enter idle=
.  In
> order to reach the deepest idle state, each cooling device has the idle
> injection threads synchronized together.
>
> It has some similarity with the intel power clamp driver but it is actual=
ly
> designed to work on the ARM architecture via the DT with a mathematical p=
roof
> with the power model which comes with the Documentation.
>
> The idle injection cycle is fixed while the running cycle is variable. Th=
at
> allows to have control on the device reactivity for the user experience. =
At
> the mitigation point the idle threads are unparked, they play idle the
> specified amount of time and they schedule themselves. The last thread se=
ts
> the next idle injection deadline and when the timer expires it wakes up a=
ll
> the threads which in turn play idle again. Meanwhile the running cycle is
> changed by set_cur_state.  When the mitigation ends, the threads are park=
ed.
> The algorithm is self adaptive, so there is no need to handle hotplugging=
.
>
> If we take an example of the balanced point, we can use the DT for the hi=
6220.
>
> The sustainable power for the SoC is 3326mW to mitigate at 75=C2=B0C. Eig=
ht cores
> running at full blast at the maximum OPP consumes 5280mW. The first value=
 is
> given in the DT, the second is calculated from the OPP with the formula:
>
>    Pdyn =3D Cdyn x Voltage^2 x Frequency
>
> As the SoC vendors don't want to share the static leakage values, we assu=
me
> it is zero, so the Prun =3D Pdyn + Pstatic =3D Pdyn + 0 =3D Pdyn.
>
> In order to reduce the power to 3326mW, we have to apply a ratio to the
> running time.
>
> ratio =3D (Prun - Ptarget) / Ptarget =3D (5280 - 3326) / 3326 =3D 0,5874
>
> We know the idle cycle which is fixed, let's assume 10ms. However from th=
is
> duration we have to substract the wake up latency for the cluster idle st=
ate.
> In our case, it is 1.5ms. So for a 10ms latency for idle, we are really i=
dle
> 8.5ms.
>
> As we know the idle duration and the ratio, we can compute the running cy=
cle.
>
>    running_cycle =3D 8.5 / 0.5874 =3D 14.47ms
>
> So for 8.5ms of idle, we have 14.47ms of running cycle, and that brings t=
he
> SoC to the balanced trip point of 75=C2=B0C.
>
> The driver has been tested on the hi6220 and it appears the temperature
> stabilizes at 75=C2=B0C with an idle injection time of 10ms (8.5ms real) =
and
> running cycle of 14ms as expected by the theory above.
>
> Signed-off-by: Kevin WangTao <kevin.wangtao@linaro.org>
> Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
> ---
>  drivers/thermal/Kconfig       |  10 +
>  drivers/thermal/cpu_cooling.c | 471 ++++++++++++++++++++++++++++++++++++=
++++++
>  include/linux/cpu_cooling.h   |   6 +
>  3 files changed, 487 insertions(+)
>
> diff --git a/drivers/thermal/Kconfig b/drivers/thermal/Kconfig
> index 925e73b..4bd4be7 100644
> --- a/drivers/thermal/Kconfig
> +++ b/drivers/thermal/Kconfig
> @@ -166,6 +166,16 @@ config CPU_FREQ_THERMAL
>           This will be useful for platforms using the generic thermal int=
erface
>           and not the ACPI interface.
>
> +config CPU_IDLE_THERMAL
> +       bool "CPU idle cooling strategy"
> +       depends on CPU_IDLE
> +       help
> +        This implements the generic CPU cooling mechanism through
> +        idle injection.  This will throttle the CPU by injecting
> +        fixed idle cycle.  All CPUs belonging to the same cluster
> +        will enter idle synchronously to reach the deepest idle
> +        state.
> +
>  endchoice
>
>  config CLOCK_THERMAL
> diff --git a/drivers/thermal/cpu_cooling.c b/drivers/thermal/cpu_cooling.=
c
> index d05bb73..916a627 100644
> --- a/drivers/thermal/cpu_cooling.c
> +++ b/drivers/thermal/cpu_cooling.c
> @@ -10,18 +10,33 @@
>   *             Viresh Kumar <viresh.kumar@linaro.org>
>   *
>   */
> +#undef DEBUG
> +#define pr_fmt(fmt) "CPU cooling: " fmt
> +
>  #include <linux/module.h>
>  #include <linux/thermal.h>
>  #include <linux/cpufreq.h>
> +#include <linux/cpuidle.h>
>  #include <linux/err.h>
> +#include <linux/freezer.h>
>  #include <linux/idr.h>
> +#include <linux/kthread.h>
>  #include <linux/pm_opp.h>
>  #include <linux/slab.h>
> +#include <linux/sched/prio.h>
> +#include <linux/sched/rt.h>
>  #include <linux/cpu.h>
>  #include <linux/cpu_cooling.h>
> +#include <linux/wait.h>
> +
> +#include <linux/platform_device.h>
> +#include <linux/of_platform.h>
>
>  #include <trace/events/thermal.h>
>
> +#include <uapi/linux/sched/types.h>
> +
> +#ifdef CONFIG_CPU_FREQ_THERMAL
>  /*
>   * Cooling state <-> CPUFreq frequency
>   *
> @@ -926,3 +941,459 @@ void cpufreq_cooling_unregister(struct thermal_cool=
ing_device *cdev)
>         kfree(cpufreq_cdev);
>  }
>  EXPORT_SYMBOL_GPL(cpufreq_cooling_unregister);
> +
> +#endif /* CPU_FREQ_THERMAL */
> +
> +#ifdef CONFIG_CPU_IDLE_THERMAL
> +/*
> + * The idle duration injection. As we don't have yet a way to specify
> + * from the DT configuration, let's default to a tick duration.
> + */
> +#define DEFAULT_IDLE_TIME_US TICK_USEC
> +
> +/**
> + * struct cpuidle_cooling_device - data for the idle cooling device
> + * @cdev: a pointer to a struct thermal_cooling_device
> + * @tsk: an array of pointer to the idle injection tasks
> + * @cpumask: a cpumask containing the CPU managed by the cooling device
> + * @timer: a hrtimer giving the tempo for the idle injection cycles
> + * @kref: a kernel refcount on this structure
> + * @waitq: the waiq for the idle injection tasks
> + * @count: an atomic to keep track of the last task exiting the idle cyc=
le
> + * @idle_cycle: an integer defining the duration of the idle injection
> + * @state: an normalized integer giving the state of the cooling device
> + */
> +struct cpuidle_cooling_device {
> +       struct thermal_cooling_device *cdev;
> +       struct task_struct **tsk;
> +       struct cpumask *cpumask;
> +       struct list_head node;
> +       struct hrtimer timer;
> +       struct kref kref;
> +       wait_queue_head_t *waitq;
> +       atomic_t count;
> +       unsigned int idle_cycle;
> +       unsigned int state;
> +};
> +
> +static LIST_HEAD(cpuidle_cdev_list);
> +
> +/**
> + * cpuidle_cooling_wakeup - Wake up all idle injection threads
> + * @idle_cdev: the idle cooling device
> + *
> + * Every idle injection task belonging to the idle cooling device and
> + * running on an online cpu will be wake up by this call.
> + */
> +static void cpuidle_cooling_wakeup(struct cpuidle_cooling_device *idle_c=
dev)
> +{
> +       int cpu;
> +       int weight =3D cpumask_weight(idle_cdev->cpumask);
> +
> +       for_each_cpu_and(cpu, idle_cdev->cpumask, cpu_online_mask)
> +               wake_up_process(idle_cdev->tsk[cpu % weight]);
> +}
> +
> +/**
> + * cpuidle_cooling_wakeup_fn - Running cycle timer callback
> + * @timer: a hrtimer structure
> + *
> + * When the mitigation is acting, the CPU is allowed to run an amount
> + * of time, then the idle injection happens for the specified delay
> + * and the idle task injection schedules itself until the timer event
> + * wakes the idle injection tasks again for a new idle injection
> + * cycle. The time between the end of the idle injection and the timer
> + * expiration is the allocated running time for the CPU.
> + *
> + * Returns always HRTIMER_NORESTART
> + */
> +static enum hrtimer_restart cpuidle_cooling_wakeup_fn(struct hrtimer *ti=
mer)
> +{
> +       struct cpuidle_cooling_device *idle_cdev =3D
> +               container_of(timer, struct cpuidle_cooling_device, timer)=
;
> +
> +       cpuidle_cooling_wakeup(idle_cdev);
> +
> +       return HRTIMER_NORESTART;
> +}
> +
> +/**
> + * cpuidle_cooling_runtime - Running time computation
> + * @idle_cdev: the idle cooling device
> + *
> + * The running duration is computed from the idle injection duration
> + * which is fixed. If we reach 100% of idle injection ratio, that
> + * means the running duration is zero. If we have a 50% ratio
> + * injection, that means we have equal duration for idle and for
> + * running duration.
> + *
> + * The formula is deduced as the following:
> + *
> + *  running =3D idle x ((100 / ratio) - 1)
> + *
> + * For precision purpose for integer math, we use the following:
> + *
> + *  running =3D (idle x 100) / ratio - idle
> + *
> + * For example, if we have an injected duration of 50%, then we end up
> + * with 10ms of idle injection and 10ms of running duration.
> + *
> + * Returns a s64 nanosecond based
> + */
> +static s64 cpuidle_cooling_runtime(struct cpuidle_cooling_device *idle_c=
dev)
> +{
> +       s64 next_wakeup;
> +       int state =3D idle_cdev->state;
> +
> +       /*
> +        * The function must never be called when there is no
> +        * mitigation because:
> +        * - that does not make sense
> +        * - we end up with a division by zero
> +        */
> +       BUG_ON(!state);
> +
> +       next_wakeup =3D (s64)((idle_cdev->idle_cycle * 100) / state) -
> +               idle_cdev->idle_cycle;
> +
> +       return next_wakeup * NSEC_PER_USEC;
> +}
> +
> +/**
> + * cpuidle_cooling_injection_thread - Idle injection mainloop thread fun=
ction
> + * @arg: a void pointer containing the idle cooling device address
> + *
> + * This main function does basically two operations:
> + *
> + * - Goes idle for a specific amount of time
> + *
> + * - Sets a timer to wake up all the idle injection threads after a
> + *   running period
> + *
> + * That happens only when the mitigation is enabled, otherwise the
> + * task is scheduled out.
> + *
> + * In order to keep the tasks synchronized together, it is the last
> + * task exiting the idle period which is in charge of setting the
> + * timer.
> + *
> + * This function never returns.
> + */
> +static int cpuidle_cooling_injection_thread(void *arg)
> +{
> +       struct sched_param param =3D { .sched_priority =3D MAX_USER_RT_PR=
IO/2 };
> +       struct cpuidle_cooling_device *idle_cdev =3D arg;
> +       int index =3D smp_processor_id() % cpumask_weight(idle_cdev->cpum=
ask);
> +       DEFINE_WAIT(wait);
> +
> +       set_freezable();
> +
> +       sched_setscheduler(current, SCHED_FIFO, &param);
> +
> +       while (1) {
> +
> +               s64 next_wakeup;
> +
> +               prepare_to_wait(&idle_cdev->waitq[index],
> +                               &wait, TASK_INTERRUPTIBLE);
> +
> +               schedule();
> +
> +               atomic_inc(&idle_cdev->count);
> +
> +               play_idle(idle_cdev->idle_cycle / USEC_PER_MSEC);
> +
> +               /*
> +                * The last CPU waking up is in charge of setting the
> +                * timer. If the CPU is hotplugged, the timer will
> +                * move to another CPU (which may not belong to the
> +                * same cluster) but that is not a problem as the
> +                * timer will be set again by another CPU belonging to
> +                * the cluster, so this mechanism is self adaptive and
> +                * does not require any hotplugging dance.
> +                */
> +               if (!atomic_dec_and_test(&idle_cdev->count))
> +                       continue;
> +
> +               if (!idle_cdev->state)
> +                       continue;
> +
> +               next_wakeup =3D cpuidle_cooling_runtime(idle_cdev);
> +
> +               hrtimer_start(&idle_cdev->timer, ns_to_ktime(next_wakeup)=
,
> +                             HRTIMER_MODE_REL_PINNED);
> +       }
> +
> +       finish_wait(&idle_cdev->waitq[index], &wait);
> +
> +       return 0;
> +}
> +
> +/**
> + * cpuidle_cooling_get_max_state - Get the maximum state
> + * @cdev  : the thermal cooling device
> + * @state : a pointer to the state variable to be filled
> + *
> + * The function gives always 100 as the injection ratio is percentile
> + * based for consistency accros different platforms.
> + *
> + * The function can not fail, it returns always zero.
> + */
> +static int cpuidle_cooling_get_max_state(struct thermal_cooling_device *=
cdev,
> +                                        unsigned long *state)
> +{
> +       /*
> +        * Depending on the configuration or the hardware, the running
> +        * cycle and the idle cycle could be different. We want unify
> +        * that to an 0..100 interval, so the set state interface will
> +        * be the same whatever the platform is.
> +        *
> +        * The state 100% will make the cluster 100% ... idle. A 0%
> +        * injection ratio means no idle injection at all and 50%
> +        * means for 10ms of idle injection, we have 10ms of running
> +        * time.
> +        */
> +       *state =3D 100;
> +
> +       return 0;
> +}
> +
> +/**
> + * cpuidle_cooling_get_cur_state - Get the current cooling state
> + * @cdev: the thermal cooling device
> + * @state: a pointer to the state
> + *
> + * The function just copy the state value from the private thermal
> + * cooling device structure, the mapping is 1 <-> 1.
> + *
> + * The function can not fail, it returns always zero.
> + */
> +static int cpuidle_cooling_get_cur_state(struct thermal_cooling_device *=
cdev,
> +                                        unsigned long *state)
> +{
> +        struct cpuidle_cooling_device *idle_cdev =3D cdev->devdata;
> +
> +       *state =3D idle_cdev->state;
> +
> +       return 0;
> +}
> +
> +/**
> + * cpuidle_cooling_set_cur_state - Set the current cooling state
> + * @cdev: the thermal cooling device
> + * @state: the target state
> + *
> + * The function checks first if we are initiating the mitigation which
> + * in turn wakes up all the idle injection tasks belonging to the idle
> + * cooling device. In any case, it updates the internal state for the
> + * cooling device.
> + *
> + * The function can not fail, it returns always zero.
> + */
> +static int cpuidle_cooling_set_cur_state(struct thermal_cooling_device *=
cdev,
> +                                        unsigned long state)
> +{
> +       struct cpuidle_cooling_device *idle_cdev =3D cdev->devdata;
> +       unsigned long current_state =3D idle_cdev->state;
> +
> +       idle_cdev->state =3D state;
> +
> +       if (current_state =3D=3D 0 && state > 0) {
> +               pr_debug("Starting cooling cpus '%*pbl'\n",
> +                        cpumask_pr_args(idle_cdev->cpumask));
> +               cpuidle_cooling_wakeup(idle_cdev);
> +       } else if (current_state > 0 && !state)  {
> +               pr_debug("Stopping cooling cpus '%*pbl'\n",
> +                        cpumask_pr_args(idle_cdev->cpumask));
> +       }
> +
> +       return 0;
> +}
> +
> +/**
> + * cpuidle_cooling_ops - thermal cooling device ops
> + */
> +static struct thermal_cooling_device_ops cpuidle_cooling_ops =3D {
> +       .get_max_state =3D cpuidle_cooling_get_max_state,
> +       .get_cur_state =3D cpuidle_cooling_get_cur_state,
> +       .set_cur_state =3D cpuidle_cooling_set_cur_state,
> +};
> +
> +/**
> + * cpuidle_cooling_release - Kref based release helper
> + * @kref: a pointer to the kref structure
> + *
> + * This function is automatically called by the kref_put function when
> + * the idle cooling device refcount reaches zero. At this point, we
> + * have the guarantee the structure is no longer in use and we can
> + * safely release all the ressources.
> + */
> +static void __init cpuidle_cooling_release(struct kref *kref)
> +{
> +       struct cpuidle_cooling_device *idle_cdev =3D
> +               container_of(kref, struct cpuidle_cooling_device, kref);
> +
> +       thermal_cooling_device_unregister(idle_cdev->cdev);
> +       kfree(idle_cdev->waitq);
> +       kfree(idle_cdev->tsk);
> +       kfree(idle_cdev);
> +}
> +
> +/**
> + * cpuidle_cooling_register - Idle cooling device initialization functio=
n
> + *
> + * This function is in charge of creating a cooling device per cluster
> + * and register it to thermal framework. For this we rely on the
> + * topology as there is nothing yet describing better the idle state
> + * power domains.
> + *
> + * For each first CPU of the cluster's cpumask, we allocate the idle
> + * cooling device, initialize the general fields and then we initialze
> + * the rest in a per cpu basis.
> + *
> + * Returns zero on success, < 0 otherwise.
> + */
> +int cpuidle_cooling_register(void)
> +{
> +       struct cpuidle_cooling_device *idle_cdev =3D NULL;
> +       struct thermal_cooling_device *cdev;
> +       struct task_struct *tsk;
> +       struct device_node *np;
> +       cpumask_t *cpumask;
> +       char dev_name[THERMAL_NAME_LENGTH];
> +       int weight;
> +       int ret =3D -ENOMEM, cpu;
> +       int index =3D 0;
> +
> +       for_each_possible_cpu(cpu) {
> +
> +               cpumask =3D topology_core_cpumask(cpu);
> +               weight =3D cpumask_weight(cpumask);
> +
> +               /*
> +                * This condition makes the first cpu belonging to the
> +                * cluster to create a cooling device and allocates
> +                * the structure. Others CPUs belonging to the same
> +                * cluster will just increment the refcount on the
> +                * cooling device structure and initialize it.
> +                */
> +               if (cpu =3D=3D cpumask_first(cpumask)) {
> +
> +                       np =3D of_cpu_device_node_get(cpu);
> +
> +                       idle_cdev =3D kzalloc(sizeof(*idle_cdev), GFP_KER=
NEL);
> +                       if (!idle_cdev)
> +                               goto out_fail;
> +
> +                       idle_cdev->tsk =3D kzalloc(sizeof(*idle_cdev->tsk=
) *
> +                                                weight, GFP_KERNEL);
> +                       if (!idle_cdev->tsk)
> +                               goto out_fail;
> +
> +                       idle_cdev->waitq =3D kzalloc(sizeof(*idle_cdev->w=
aitq) *
> +                                                  weight, GFP_KERNEL);
> +                       if (!idle_cdev->waitq)
> +                               goto out_fail;
> +
> +                       idle_cdev->idle_cycle =3D DEFAULT_IDLE_TIME_US;
> +
> +                       atomic_set(&idle_cdev->count, 0);
> +
> +                       kref_init(&idle_cdev->kref);
> +
> +                       /*
> +                        * Initialize the timer to wakeup all the idle
> +                        * injection tasks
> +                        */
> +                       hrtimer_init(&idle_cdev->timer,
> +                                    CLOCK_MONOTONIC, HRTIMER_MODE_REL);
> +
> +                       /*
> +                        * The wakeup function callback which is in
> +                        * charge of waking up all CPUs belonging to
> +                        * the same cluster
> +                        */
> +                       idle_cdev->timer.function =3D cpuidle_cooling_wak=
eup_fn;
> +
> +                       /*
> +                        * The thermal cooling device name
> +                        */
> +                       snprintf(dev_name, sizeof(dev_name), "thermal-idl=
e-%d", index++);
> +                       cdev =3D thermal_of_cooling_device_register(np, d=
ev_name,
> +                                                                 idle_cd=
ev,
> +                                                                 &cpuidl=
e_cooling_ops);
> +                       if (IS_ERR(cdev)) {
> +                               ret =3D PTR_ERR(cdev);
> +                               goto out_fail;
> +                       }
> +
> +                       idle_cdev->cdev =3D cdev;
> +
> +                       idle_cdev->cpumask =3D cpumask;
> +
> +                       list_add(&idle_cdev->node, &cpuidle_cdev_list);
> +
> +                       pr_info("Created idle cooling device for cpus '%*=
pbl'\n",
> +                               cpumask_pr_args(cpumask));
> +               }
> +
> +               kref_get(&idle_cdev->kref);
> +
> +               /*
> +                * Each cooling device is per package. Each package
> +                * has a set of cpus where the physical number is
> +                * duplicate in the kernel namespace. We need a way to
> +                * address the waitq[] and tsk[] arrays with index
> +                * which are not Linux cpu numbered.
> +                *
> +                * One solution is to use the
> +                * topology_core_id(cpu). Other solution is to use the
> +                * modulo.
> +                *
> +                * eg. 2 x cluster - 4 cores.
> +                *
> +                * Physical numbering -> Linux numbering -> % nr_cpus
> +                *
> +                * Pkg0 - Cpu0 -> 0 -> 0
> +                * Pkg0 - Cpu1 -> 1 -> 1
> +                * Pkg0 - Cpu2 -> 2 -> 2
> +                * Pkg0 - Cpu3 -> 3 -> 3
> +                *
> +                * Pkg1 - Cpu0 -> 4 -> 0
> +                * Pkg1 - Cpu1 -> 5 -> 1
> +                * Pkg1 - Cpu2 -> 6 -> 2
> +                * Pkg1 - Cpu3 -> 7 -> 3


I'm not sure that the assumption above for the CPU numbering is safe.
Can't you use a per cpu structure to point to resources that are per
cpu instead ? so you will not have to rely on CPU ordering


> +                */
> +               init_waitqueue_head(&idle_cdev->waitq[cpu % weight]);
> +
> +               tsk =3D kthread_create_on_cpu(cpuidle_cooling_injection_t=
hread,
> +                                           idle_cdev, cpu, "kidle_inject=
/%u");
> +               if (IS_ERR(tsk)) {
> +                       ret =3D PTR_ERR(tsk);
> +                       goto out_fail;
> +               }
> +
> +               idle_cdev->tsk[cpu % weight] =3D tsk;
> +
> +               wake_up_process(tsk);
> +       }
> +
> +       return 0;
> +
> +out_fail:
> +       list_for_each_entry(idle_cdev, &cpuidle_cdev_list, node) {
> +
> +               for_each_cpu(cpu, idle_cdev->cpumask) {
> +
> +                       if (idle_cdev->tsk[cpu])
> +                               kthread_stop(idle_cdev->tsk[cpu]);
> +
> +                       kref_put(&idle_cdev->kref, cpuidle_cooling_releas=
e);
> +               }
> +       }
> +
> +       pr_err("Failed to create idle cooling device (%d)\n", ret);
> +
> +       return ret;
> +}
> +#endif
> diff --git a/include/linux/cpu_cooling.h b/include/linux/cpu_cooling.h
> index d4292eb..2b5950b 100644
> --- a/include/linux/cpu_cooling.h
> +++ b/include/linux/cpu_cooling.h
> @@ -45,6 +45,7 @@ struct thermal_cooling_device *
>  cpufreq_power_cooling_register(struct cpufreq_policy *policy,
>                                u32 capacitance, get_static_t plat_static_=
func);
>
> +extern int cpuidle_cooling_register(void);
>  /**
>   * of_cpufreq_cooling_register - create cpufreq cooling device based on =
DT.
>   * @np: a valid struct device_node to the cooling device device tree nod=
e.
> @@ -118,6 +119,11 @@ void cpufreq_cooling_unregister(struct thermal_cooli=
ng_device *cdev)
>  {
>         return;
>  }
> +
> +static inline int cpuidle_cooling_register(void)
> +{
> +       return 0;
> +}
>  #endif /* CONFIG_CPU_THERMAL */
>
>  #endif /* __CPU_COOLING_H__ */
> --
> 2.7.4
>