LXR linux/tools/leds/led_hw_brightness

   1// SPDX-License-Identifier: GPL-2.0
   2/*
   3 * led_hw_brightness_mon.c
   4 *
   5 * This program monitors LED brightness level changes having its origin
   6 * in hardware/firmware, i.e. outside of kernel control.
   7 * A timestamp and brightness value is printed each time the brightness changes.
   8 *
   9 * Usage: led_hw_brightness_mon <device-name>
  10 *
  11 * <device-name> is the name of the LED class device to be monitored. Pressing
  12 * CTRL+C will exit.
  13 */
  14
  15#include <errno.h>
  16#include <fcntl.h>
  17#include <poll.h>
  18#include <stdio.h>
  19#include <stdlib.h>
  20#include <string.h>
  21#include <time.h>
  22#include <unistd.h>
  23
  24#include <linux/uleds.h>
  25
  26int main(int argc, char const *argv[])
  27{
  28        int fd, ret;
  29        char brightness_file_path[LED_MAX_NAME_SIZE + 11];
  30        struct pollfd pollfd;
  31        struct timespec ts;
  32        char buf[11];
  33
  34        if (argc != 2) {
  35                fprintf(stderr, "Requires <device-name> argument\n");
  36                return 1;
  37        }
  38
  39        snprintf(brightness_file_path, LED_MAX_NAME_SIZE,
  40                 "/sys/class/leds/%s/brightness_hw_changed", argv[1]);
  41
  42        fd = open(brightness_file_path, O_RDONLY);
  43        if (fd == -1) {
  44                printf("Failed to open %s file\n", brightness_file_path);
  45                return 1;
  46        }
  47
  48        /*
  49         * read may fail if no hw brightness change has occurred so far,
  50         * but it is required to avoid spurious poll notifications in
  51         * the opposite case.
  52         */
  53        read(fd, buf, sizeof(buf));
  54
  55        pollfd.fd = fd;
  56        pollfd.events = POLLPRI;
  57
  58        while (1) {
  59                ret = poll(&pollfd, 1, -1);
  60                if (ret == -1) {
  61                        printf("Failed to poll %s file (%d)\n",
  62                                brightness_file_path, ret);
  63                        ret = 1;
  64                        break;
  65                }
  66
  67                clock_gettime(CLOCK_MONOTONIC, &ts);
  68
  69                ret = read(fd, buf, sizeof(buf));
  70                if (ret < 0)
  71                        break;
  72
  73                ret = lseek(pollfd.fd, 0, SEEK_SET);
  74                if (ret < 0) {
  75                        printf("lseek failed (%d)\n", ret);
  76                        break;
  77                }
  78
  79                printf("[%ld.%09ld] %d\n", ts.tv_sec, ts.tv_nsec, atoi(buf));
  80        }
  81
  82        close(fd);
  83
  84        return ret;
  85}
  86