Re: [RFC][PATCH 4/5] thermal: Add support for setting polling interval

[Amit Kucheria <amit.kucheria@verdurent.com>]

On Mon, May 4, 2020 at 11:47 PM Srinivas Pandruvada
<srinivas.pandruvada@linux.intel.com> wrote:
>
> Add new attribute in the thermal syfs for setting temperature sampling
> interval when CONFIG_THERMAL_USER_EVENT_INTERFACE is defined. The default
> value is 0, which means no polling.
>
> At this interval user space will get an event THERMAL_TEMP_SAMPLE with
> temperature sample. This reuses existing polling mecahnism when polling
> or passive delay is specified during zone registry. To avoid interference
> with passive and polling delay, this new polling attribute can't be used
> for those zones.

Why should the kernel periodically emit events for userspace when the
userspace is perfectly capable of deciding how frequently it wants to
poll a file for changes?

>
> Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
> ---
>  drivers/thermal/thermal_core.c  |  7 +++++++
>  drivers/thermal/thermal_sysfs.c | 36 +++++++++++++++++++++++++++++++--
>  include/linux/thermal.h         |  1 +
>  3 files changed, 42 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/thermal/thermal_core.c b/drivers/thermal/thermal_core.c
> index 14770d882d42..17cd799b0073 100644
> --- a/drivers/thermal/thermal_core.c
> +++ b/drivers/thermal/thermal_core.c
> @@ -313,6 +313,8 @@ static void monitor_thermal_zone(struct thermal_zone_device *tz)
>                 thermal_zone_device_set_polling(tz, tz->passive_delay);
>         else if (tz->polling_delay)
>                 thermal_zone_device_set_polling(tz, tz->polling_delay);
> +       else if (tz->temp_polling_delay)
> +               thermal_zone_device_set_polling(tz, tz->temp_polling_delay);
>         else
>                 thermal_zone_device_set_polling(tz, 0);
>
> @@ -446,6 +448,11 @@ static void update_temperature(struct thermal_zone_device *tz)
>         tz->temperature = temp;
>         mutex_unlock(&tz->lock);
>
> +       if (tz->temp_polling_delay) {
> +               thermal_dev_send_event(tz->id, THERMAL_TEMP_SAMPLE, temp);
> +               monitor_thermal_zone(tz);
> +       }
> +
>         trace_thermal_temperature(tz);
>         if (tz->last_temperature == THERMAL_TEMP_INVALID)
>                 dev_dbg(&tz->device, "last_temperature N/A, current_temperature=%d\n",
> diff --git a/drivers/thermal/thermal_sysfs.c b/drivers/thermal/thermal_sysfs.c
> index aa85424c3ac4..0df7997993fe 100644
> --- a/drivers/thermal/thermal_sysfs.c
> +++ b/drivers/thermal/thermal_sysfs.c
> @@ -248,6 +248,36 @@ create_thres_attr(temp_thres_low);
>  create_thres_attr(temp_thres_high);
>  create_thres_attr(temp_thres_hyst);
>
> +static ssize_t
> +temp_polling_delay_store(struct device *dev, struct device_attribute *attr,
> +                  const char *buf, size_t count)
> +{
> +       struct thermal_zone_device *tz = to_thermal_zone(dev);
> +       int val;
> +
> +       if (kstrtoint(buf, 10, &val))
> +               return -EINVAL;
> +
> +       if (val && val < 1000)
> +               return -EINVAL;
> +
> +       tz->temp_polling_delay = val;
> +       thermal_zone_device_update(tz, THERMAL_EVENT_UNSPECIFIED);
> +
> +       return count;
> +}
> +
> +static ssize_t
> +temp_polling_delay_show(struct device *dev, struct device_attribute *attr,
> +                    char *buf)
> +{
> +       struct thermal_zone_device *tz = to_thermal_zone(dev);
> +
> +       return sprintf(buf, "%d\n", tz->temp_polling_delay);
> +}
> +
> +static DEVICE_ATTR_RW(temp_polling_delay);
> +
>  static int create_user_events_attrs(struct thermal_zone_device *tz)
>  {
>         struct attribute **attrs;
> @@ -260,8 +290,8 @@ static int create_user_events_attrs(struct thermal_zone_device *tz)
>         if (tz->ops->get_temp_thres_high)
>                 ++index;
>
> -       /* One additional space for NULL */
> -       attrs = kcalloc(index + 1, sizeof(*attrs), GFP_KERNEL);
> +       /* One additional space for NULL and temp_pollling_delay */
> +       attrs = kcalloc(index + 2, sizeof(*attrs), GFP_KERNEL);
>         if (!attrs)
>                 return -ENOMEM;
>
> @@ -312,6 +342,8 @@ static int create_user_events_attrs(struct thermal_zone_device *tz)
>                 attrs[index] = &tz->threshold_attrs[index].attr.attr;
>                 ++index;
>         }
> +       if (!tz->polling_delay && !tz->passive_delay)
> +               attrs[index++] = &dev_attr_temp_polling_delay.attr;
>         attrs[index] = NULL;
>         tz->threshold_attribute_group.attrs = attrs;
>
> diff --git a/include/linux/thermal.h b/include/linux/thermal.h
> index ee9d79ace7ce..0ec4bd8c9c5c 100644
> --- a/include/linux/thermal.h
> +++ b/include/linux/thermal.h
> @@ -216,6 +216,7 @@ struct thermal_zone_device {
>         enum thermal_notify_event notify_event;
>         struct attribute_group threshold_attribute_group;
>         struct thermal_attr *threshold_attrs;
> +       int temp_polling_delay;
>  };
>
>  /**
> --
> 2.25.4
>