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ae3473231e
LED subsystem supports POLLPRI on "brightness_hw_changed" sysfs file of LED class devices. This tool demonstrates how to use the feature. Signed-off-by: Jacek Anaszewski <jacek.anaszewski@gmail.com> Acked-by: Hans de Goede <hdegoede@redhat.com> Acked-by: Pavel Machek <pavel@ucw.cz>
85 lines
1.7 KiB
C
85 lines
1.7 KiB
C
/*
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* led_hw_brightness_mon.c
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*
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* This program monitors LED brightness level changes having its origin
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* in hardware/firmware, i.e. outside of kernel control.
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* A timestamp and brightness value is printed each time the brightness changes.
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*
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* Usage: led_hw_brightness_mon <device-name>
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*
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* <device-name> is the name of the LED class device to be monitored. Pressing
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* CTRL+C will exit.
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*/
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#include <errno.h>
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#include <fcntl.h>
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#include <poll.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <time.h>
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#include <unistd.h>
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#include <linux/uleds.h>
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int main(int argc, char const *argv[])
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{
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int fd, ret;
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char brightness_file_path[LED_MAX_NAME_SIZE + 11];
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struct pollfd pollfd;
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struct timespec ts;
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char buf[11];
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if (argc != 2) {
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fprintf(stderr, "Requires <device-name> argument\n");
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return 1;
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}
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snprintf(brightness_file_path, LED_MAX_NAME_SIZE,
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"/sys/class/leds/%s/brightness_hw_changed", argv[1]);
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fd = open(brightness_file_path, O_RDONLY);
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if (fd == -1) {
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printf("Failed to open %s file\n", brightness_file_path);
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return 1;
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}
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/*
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* read may fail if no hw brightness change has occurred so far,
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* but it is required to avoid spurious poll notifications in
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* the opposite case.
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*/
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read(fd, buf, sizeof(buf));
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pollfd.fd = fd;
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pollfd.events = POLLPRI;
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while (1) {
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ret = poll(&pollfd, 1, -1);
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if (ret == -1) {
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printf("Failed to poll %s file (%d)\n",
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brightness_file_path, ret);
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ret = 1;
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break;
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}
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clock_gettime(CLOCK_MONOTONIC, &ts);
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ret = read(fd, buf, sizeof(buf));
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if (ret < 0)
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break;
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ret = lseek(pollfd.fd, 0, SEEK_SET);
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if (ret < 0) {
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printf("lseek failed (%d)\n", ret);
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break;
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}
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printf("[%ld.%09ld] %d\n", ts.tv_sec, ts.tv_nsec, atoi(buf));
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}
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close(fd);
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return ret;
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}
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