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