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