tools/leds/led_hw_brightness_mon.c

   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
  26 int 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 }