Re: [RFC][PATCH 1/5] thermal: Add support for /dev/thermal_notify

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

On Mon, May 4, 2020 at 11:47 PM Srinivas Pandruvada
<srinivas.pandruvada@linux.intel.com> wrote:
>
> This change adds an optional feature to add a new device entry
> /dev/thermal_notify.
>
> When config CONFIG_THERMAL_USER_EVENT_INTERFACE is selected, this new
> device entry is created.
>
> Thermal core or any thermal driver can use thermal_dev_send_event() interface

Do you have any particular use case in mind where a platform driver
will use this interface to send platform-specific events?

IMO, we should probably try to keep this restricted to messages from
thermal core if we are to have any hope of having a standard library
in userspace capable of parsing these thermal events.

> to send events. Each user events follows a standard format:
> - zone_id
> - event_id
> - event_data
> - reserved for future, currently 0s
>
> User space can basically:
>         fd = open ("/dev/thermal_notify")
>         In a loop
>                 read (fd)
>                         read and process event
>
> or
>         fd = open ("/dev/thermal_notify")
>         Set the fs as non blocking
>         In a loop
>                 Use poll() and wait
>                         read and process event
>
> There are predefined events added to thermal.h. Based on need they can
> be extended.
>
> Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
> ---
>  drivers/thermal/Kconfig          |   9 ++
>  drivers/thermal/Makefile         |   3 +
>  drivers/thermal/thermal_dev_if.c | 195 +++++++++++++++++++++++++++++++
>  include/linux/thermal.h          |  24 ++++
>  4 files changed, 231 insertions(+)
>  create mode 100644 drivers/thermal/thermal_dev_if.c
>
> diff --git a/drivers/thermal/Kconfig b/drivers/thermal/Kconfig
> index 91af271e9bb0..27d05d62458e 100644
> --- a/drivers/thermal/Kconfig
> +++ b/drivers/thermal/Kconfig
> @@ -78,6 +78,15 @@ config THERMAL_WRITABLE_TRIPS
>           Say 'Y' here if you would like to allow userspace tools to
>           change trip temperatures.
>
> +config THERMAL_USER_EVENT_INTERFACE
> +       bool "Allow user space to read thermal events from a dev file"
> +       help
> +         This option allows a user space program to read thermal events
> +         via /dev/thermal_notify file.
> +
> +         Say 'Y' here if you would like to allow userspace programs to
> +         read thermal events.
> +
>  choice
>         prompt "Default Thermal governor"
>         default THERMAL_DEFAULT_GOV_STEP_WISE
> diff --git a/drivers/thermal/Makefile b/drivers/thermal/Makefile
> index 8c8ed7b79915..8f65832d755a 100644
> --- a/drivers/thermal/Makefile
> +++ b/drivers/thermal/Makefile
> @@ -11,6 +11,9 @@ thermal_sys-y                 += thermal_core.o thermal_sysfs.o \
>  thermal_sys-$(CONFIG_THERMAL_HWMON)            += thermal_hwmon.o
>  thermal_sys-$(CONFIG_THERMAL_OF)               += of-thermal.o
>
> +# Thermal user space events
> +obj-$(CONFIG_THERMAL_USER_EVENT_INTERFACE)     += thermal_dev_if.o
> +
>  # governors
>  thermal_sys-$(CONFIG_THERMAL_GOV_FAIR_SHARE)   += fair_share.o
>  thermal_sys-$(CONFIG_THERMAL_GOV_BANG_BANG)    += gov_bang_bang.o
> diff --git a/drivers/thermal/thermal_dev_if.c b/drivers/thermal/thermal_dev_if.c
> new file mode 100644
> index 000000000000..763bfe9eef9d
> --- /dev/null
> +++ b/drivers/thermal/thermal_dev_if.c
> @@ -0,0 +1,195 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Thermal device file interface
> + * Copyright (c) 2020, Intel Corporation.
> + * All rights reserved.
> + *
> + * Author: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
> + */
> +
> +#include <linux/init.h>
> +#include <linux/kfifo.h>
> +#include <linux/miscdevice.h>
> +#include <linux/poll.h>
> +#include <linux/slab.h>
> +#include <linux/thermal.h>
> +#include <linux/wait.h>
> +
> +#define THERMAL_DEV_FIFO_SIZE  1024
> +
> +struct thermal_chdev_sample {
> +       int zone_id;
> +       int event;
> +       u64 event_data;
> +       u64 reserved;
> +};
> +
> +struct thermal_chdev {
> +       struct miscdevice therm_dev;
> +       struct kfifo data_fifo;
> +       unsigned long misc_opened;
> +       wait_queue_head_t wait;
> +};
> +
> +static DEFINE_MUTEX(thermal_chdev_mutex);
> +static struct thermal_chdev *thermal_chdev;
> +
> +static int thermal_chdev_open(struct inode *inode, struct file *file)
> +{
> +       struct thermal_chdev *chdev;
> +
> +       chdev = container_of(file->private_data, struct thermal_chdev, therm_dev);
> +
> +       /* We essentially have single reader and writer */
> +       if (test_and_set_bit(0, &chdev->misc_opened))
> +               return -EBUSY;
> +
> +       return stream_open(inode, file);
> +}
> +
> +static int thermal_chdev_release(struct inode *inode, struct file *file)
> +{
> +       struct thermal_chdev *chdev;
> +
> +       chdev = container_of(file->private_data, struct thermal_chdev, therm_dev);
> +
> +       clear_bit(0, &chdev->misc_opened);
> +
> +       return 0;
> +}
> +
> +static __poll_t thermal_chdev_poll(struct file *file, struct poll_table_struct *wait)
> +{
> +       struct thermal_chdev *chdev;
> +       __poll_t mask = 0;
> +
> +       chdev = container_of(file->private_data, struct thermal_chdev, therm_dev);
> +
> +       poll_wait(file, &chdev->wait, wait);
> +
> +       if (!kfifo_is_empty(&chdev->data_fifo))
> +               mask = EPOLLIN | EPOLLRDNORM;
> +
> +       return mask;
> +}
> +
> +static ssize_t thermal_chdev_read(struct file *file, char __user *buf, size_t count, loff_t *f_ps)
> +{
> +       struct thermal_chdev *chdev;
> +       unsigned int copied;
> +       int ret;
> +
> +       chdev = container_of(file->private_data, struct thermal_chdev, therm_dev);
> +
> +       if (count < sizeof(struct thermal_chdev_sample))
> +               return -EINVAL;
> +
> +       do {
> +               if (kfifo_is_empty(&chdev->data_fifo)) {
> +                       if (file->f_flags & O_NONBLOCK)
> +                               return -EAGAIN;
> +
> +                       ret = wait_event_interruptible(chdev->wait, !kfifo_is_empty(&chdev->data_fifo));
> +                       if (ret)
> +                               return ret;
> +               }
> +               ret = kfifo_to_user(&chdev->data_fifo, buf, count, &copied);
> +               if (ret)
> +                       return ret;
> +
> +       } while (copied == 0);
> +
> +       return copied;
> +}
> +
> +static int thermal_chdev_capture_sample(struct thermal_chdev *chdev, struct thermal_chdev_sample *sample)
> +{
> +       int ret = 0;
> +
> +       if (!test_bit(0, &chdev->misc_opened))
> +               return 0;
> +
> +       mutex_lock(&thermal_chdev_mutex);
> +       if (kfifo_avail(&chdev->data_fifo) >= sizeof(*sample)) {
> +               kfifo_in(&chdev->data_fifo, (unsigned char *)sample, sizeof(*sample));
> +               wake_up(&chdev->wait);
> +       } else {
> +               ret =  -ENOMEM;
> +       }
> +       mutex_unlock(&thermal_chdev_mutex);
> +
> +       return ret;
> +}
> +
> +static const struct file_operations thermal_chdev_fops = {
> +       .open =  thermal_chdev_open,
> +       .read =  thermal_chdev_read,
> +       .release = thermal_chdev_release,
> +       .poll = thermal_chdev_poll,
> +       .llseek = noop_llseek,
> +};
> +
> +static int thermal_dev_if_add(void)
> +{
> +       int ret;
> +
> +       if (thermal_chdev)
> +               return 0;
> +
> +       thermal_chdev = kzalloc(sizeof(*thermal_chdev), GFP_KERNEL);
> +       if (!thermal_chdev)
> +               return -ENOMEM;
> +
> +       ret = kfifo_alloc(&thermal_chdev->data_fifo, THERMAL_DEV_FIFO_SIZE, GFP_KERNEL);
> +       if (ret)
> +               goto free_mem;
> +
> +       init_waitqueue_head(&thermal_chdev->wait);
> +
> +       thermal_chdev->therm_dev.minor = MISC_DYNAMIC_MINOR;
> +       thermal_chdev->therm_dev.name = "thermal_notify";
> +       thermal_chdev->therm_dev.fops = &thermal_chdev_fops;
> +       ret = misc_register(&thermal_chdev->therm_dev);
> +       if (ret) {
> +               kfifo_free(&thermal_chdev->data_fifo);
> +               goto free_mem;
> +       }
> +
> +       return 0;
> +
> +free_mem:
> +       kfree(thermal_chdev);
> +       thermal_chdev = NULL;
> +       return ret;
> +}
> +
> +/**
> + * thermal_dev_send_event() - Send thermal event to user space
> + * @zone_id:   Zone id of the caller
> + * @event:     A predefined thermal event
> + * @event_data: Event specific data
> + *
> + * An interface to send event to user space with an optional associated
> + * data.
> + *
> + * Return: 0 on success, other values on error.
> + */
> +int thermal_dev_send_event(int zone_id, enum thermal_device_events event, u64 event_data)
> +{
> +       struct thermal_chdev_sample sample;
> +
> +       if (!thermal_chdev) {
> +               int ret;
> +
> +               ret = thermal_dev_if_add();
> +               if (ret)
> +                       return ret;
> +       }
> +
> +       sample.zone_id = zone_id;
> +       sample.event = event;
> +       sample.event_data = event_data;
> +       sample.reserved = 0;
> +       return thermal_chdev_capture_sample(thermal_chdev, &sample);
> +}
> +EXPORT_SYMBOL_GPL(thermal_dev_send_event);
> diff --git a/include/linux/thermal.h b/include/linux/thermal.h
> index c91b1e344d56..f5e1e7c6a9a2 100644
> --- a/include/linux/thermal.h
> +++ b/include/linux/thermal.h
> @@ -543,4 +543,28 @@ static inline void thermal_notify_framework(struct thermal_zone_device *tz,
>  { }
>  #endif /* CONFIG_THERMAL */
>
> +enum thermal_device_events {
> +       THERMAL_TEMP_SAMPLE = 0,
> +       THERMAL_ZONE_CREATE,
> +       THERMAL_ZONE_DELETE,
> +       THERMAL_ZONE_DISABLED,
> +       THERMAL_ZONE_ENABLED,
> +       THERMAL_TEMP_LOW_THRES,
> +       THERMAL_TEMP_HIGH_THRES,
> +       THERMAL_TRIP_ADD,
> +       THERMAL_TRIP_DELETE,
> +       THERMAL_TRIP_UPDATE,
> +       THERMAL_TRIP_REACHED,
> +       THERMAL_PERF_CHANGED,
> +};
> +
> +#ifdef CONFIG_THERMAL_USER_EVENT_INTERFACE
> +int thermal_dev_send_event(int zone_id, enum thermal_device_events event, u64 event_data);
> +#else
> +int thermal_dev_send_event(int zone_id, enum thermal_device_events event, u64 event_data)
> +{
> +       return 0;
> +}
> +#endif
> +
>  #endif /* __THERMAL_H__ */
> --
> 2.25.4
>