Quelle  heartbeat.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Simple heartbeat STM source driver
 * Copyright (c) 2016, Intel Corporation.
 *
 * Heartbeat STM source will send repetitive messages over STM devices to a
 * trace host.
 */

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/hrtimer.h>
#include <linux/slab.h>
#include <linux/stm.h>

#define STM_HEARTBEAT_MAX 32

static int nr_devs = 4;
static int interval_ms = 10;

module_param(nr_devs, int, 0400);
module_param(interval_ms, int, 0600);

static struct stm_heartbeat {
 struct stm_source_data data;
 struct hrtimer  hrtimer;
 unsigned int  active;
} stm_heartbeat[STM_HEARTBEAT_MAX];

static const char str[] = "heartbeat stm source driver is here to serve you";

static enum hrtimer_restart stm_heartbeat_hrtimer_handler(struct hrtimer *hr)
{
 struct stm_heartbeat *heartbeat = container_of(hr, struct stm_heartbeat,
             hrtimer);

 stm_source_write(&heartbeat->data, 0, str, sizeof str);
 if (heartbeat->active)
  hrtimer_forward_now(hr, ms_to_ktime(interval_ms));

 return heartbeat->active ? HRTIMER_RESTART : HRTIMER_NORESTART;
}

static int stm_heartbeat_link(struct stm_source_data *data)
{
 struct stm_heartbeat *heartbeat =
  container_of(data, struct stm_heartbeat, data);

 heartbeat->active = 1;
 hrtimer_start(&heartbeat->hrtimer, ms_to_ktime(interval_ms),
        HRTIMER_MODE_ABS);

 return 0;
}

static void stm_heartbeat_unlink(struct stm_source_data *data)
{
 struct stm_heartbeat *heartbeat =
  container_of(data, struct stm_heartbeat, data);

 heartbeat->active = 0;
 hrtimer_cancel(&heartbeat->hrtimer);
}

static int stm_heartbeat_init(void)
{
 int i, ret;

 if (nr_devs < 0 || nr_devs > STM_HEARTBEAT_MAX)
  return -EINVAL;

 for (i = 0; i < nr_devs; i++) {
  stm_heartbeat[i].data.name =
   kasprintf(GFP_KERNEL, "heartbeat.%d", i);
  if (!stm_heartbeat[i].data.name) {
   ret = -ENOMEM;
   goto fail_unregister;
  }

  stm_heartbeat[i].data.nr_chans = 1;
  stm_heartbeat[i].data.type = STM_USER;
  stm_heartbeat[i].data.link = stm_heartbeat_link;
  stm_heartbeat[i].data.unlink = stm_heartbeat_unlink;
  hrtimer_setup(&stm_heartbeat[i].hrtimer, stm_heartbeat_hrtimer_handler,
         CLOCK_MONOTONIC, HRTIMER_MODE_ABS);

  ret = stm_source_register_device(NULL, &stm_heartbeat[i].data);
  if (ret)
   goto fail_free;
 }

 return 0;

fail_unregister:
 for (i--; i >= 0; i--) {
  stm_source_unregister_device(&stm_heartbeat[i].data);
fail_free:
  kfree(stm_heartbeat[i].data.name);
 }

 return ret;
}

static void stm_heartbeat_exit(void)
{
 int i;

 for (i = 0; i < nr_devs; i++) {
  stm_source_unregister_device(&stm_heartbeat[i].data);
  kfree(stm_heartbeat[i].data.name);
 }
}

module_init(stm_heartbeat_init);
module_exit(stm_heartbeat_exit);

MODULE_LICENSE("GPL v2");
MODULE_DESCRIPTION("stm_heartbeat driver");
MODULE_AUTHOR("Alexander Shishkin <alexander.shishkin@linux.intel.com>");