linux-kernel - Re: [PATCH v3 1/4] devfreq: Register devfreq as a cooling device on demand

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Date:   Sun, 7 Mar 2021 23:16:13 +0900
From:   Chanwoo Choi <cwchoi00@...il.com>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:     Lukasz Luba <lukasz.luba@....com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Linux PM list <linux-pm@...r.kernel.org>,
        Steven Price <steven.price@....com>,
        MyungJoo Ham <myungjoo.ham@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Chanwoo Choi <cw00.choi@...sung.com>
Subject: Re: [PATCH v3 1/4] devfreq: Register devfreq as a cooling device on demand

On 21. 3. 7. 오후 6:45, Daniel Lezcano wrote:
> Currently the default behavior is to manually having the devfreq
> backend to register themselves as a devfreq cooling device.
>
> Instead of adding the code in the drivers for the thermal cooling
> device registering, let's provide a flag in the devfreq's profile to
> tell the common devfreq code to register the newly created devfreq as
> a cooling device.
>
> Suggested-by: Chanwoo Choi <cwchoi00@...il.com>
> Signed-off-by: Daniel Lezcano <daniel.lezcano@...aro.org>
> ---
>   V3:
>     - Rebased on linux-pm branch without units.h
>     - Set the cdev to NULL in case of error
>     - Added description for the cdev field in the devfreq structure
>   V2:
>     - Added is_cooling_device boolean in profile structure
>     - Register cooling device when the is_cooling_device boolean is set
>     - Remove devfreq cooling device registration in the backend drivers
>   V1:
>     - Register devfreq as a cooling device unconditionnally
> ---
>   drivers/devfreq/devfreq.c | 13 +++++++++++++
>   include/linux/devfreq.h   |  8 ++++++++
>   2 files changed, 21 insertions(+)
>
> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
> index bf3047896e41..cf64aeec468f 100644
> --- a/drivers/devfreq/devfreq.c
> +++ b/drivers/devfreq/devfreq.c
> @@ -11,6 +11,7 @@
>   #include <linux/kmod.h>
>   #include <linux/sched.h>
>   #include <linux/debugfs.h>
> +#include <linux/devfreq_cooling.h>
>   #include <linux/errno.h>
>   #include <linux/err.h>
>   #include <linux/init.h>
> @@ -26,6 +27,7 @@
>   #include <linux/hrtimer.h>
>   #include <linux/of.h>
>   #include <linux/pm_qos.h>
> +#include <linux/thermal.h>
>   #include "governor.h"
>
>   #define CREATE_TRACE_POINTS
> @@ -935,6 +937,15 @@ struct devfreq *devfreq_add_device(struct device *dev,
>
>       mutex_unlock(&devfreq_list_lock);
>
> +     if (devfreq->profile->is_cooling_device) {
> +             devfreq->cdev = devfreq_cooling_em_register(devfreq, NULL);
> +             if (IS_ERR(devfreq->cdev)) {
> +                     dev_info(dev, "Failed to register devfreq "
> +                              "cooling device\n");
> +                     devfreq->cdev = NULL;
> +             }
> +     }
> +
>       return devfreq;
>
>   err_init:
> @@ -960,6 +971,8 @@ int devfreq_remove_device(struct devfreq *devfreq)
>       if (!devfreq)
>               return -EINVAL;
>
> +     thermal_cooling_device_unregister(devfreq->cdev);

I have a question. Why don't you use devfreq_cooling_unregister()?
When thermal_cooling_device_unregister(), how can we remove
the pm_qos_request of devfreq device?

> +
>       if (devfreq->governor) {
>               devfreq->governor->event_handler(devfreq,
>                                                DEVFREQ_GOV_STOP, NULL);
> diff --git a/include/linux/devfreq.h b/include/linux/devfreq.h
> index 26ea0850be9b..aba7ace11b72 100644
> --- a/include/linux/devfreq.h
> +++ b/include/linux/devfreq.h
> @@ -98,11 +98,15 @@ struct devfreq_dev_status {
>    * @freq_table:             Optional list of frequencies to support statistics
>    *                  and freq_table must be generated in ascending order.
>    * @max_state:              The size of freq_table.
> + *
> + * @is_cooling_device: A self-explanatory boolean giving the device a
> + *                     cooling effect property.
>    */
>   struct devfreq_dev_profile {
>       unsigned long initial_freq;
>       unsigned int polling_ms;
>       enum devfreq_timer timer;
> +     bool is_cooling_device;
>
>       int (*target)(struct device *dev, unsigned long *freq, u32 flags);
>       int (*get_dev_status)(struct device *dev,
> @@ -156,6 +160,7 @@ struct devfreq_stats {
>    * @suspend_count:   suspend requests counter for a device.
>    * @stats:  Statistics of devfreq device behavior
>    * @transition_notifier_list: list head of DEVFREQ_TRANSITION_NOTIFIER notifier
> + * @cdev:    Cooling device pointer if the devfreq has cooling property
>    * @nb_min:         Notifier block for DEV_PM_QOS_MIN_FREQUENCY
>    * @nb_max:         Notifier block for DEV_PM_QOS_MAX_FREQUENCY
>    *
> @@ -198,6 +203,9 @@ struct devfreq {
>
>       struct srcu_notifier_head transition_notifier_list;
>
> +     /* Pointer to the cooling device if used for thermal mitigation */
> +     struct thermal_cooling_device *cdev;
> +
>       struct notifier_block nb_min;
>       struct notifier_block nb_max;
>   };
>


--
Best Regards,
Samsung Electronics

Chanwoo Choi