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 }
86
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