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