iio: event_monitor: Enable events before monitoring

After some painful sessions with a driver that register an
enable/disable sysfs knob (gp2ap002) and manually going
in and enabling the event before monitoring it:

cd /sys/bus/iio/devices/iio\:device2/events
# ls
in_proximity_thresh_either_en
# echo 1 > in_proximity_thresh_either_en

I realized that it's better if the iio_event_monitor is
smart enough to enable all events by itself and disable them
after use, if passed the -a flag familiar from the
iio_generic_buffer tool.

Auto-enabling events depend on the hardware being able
to handle all events at the same time which isn't
necessarily the case, so a command line option is required
for this.

Cc: Bastien Nocera <[e-mail]>
Signed-off-by: Linus Walleij <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jonathan Cameron <[e-mail]>

tools/iio/iio_event_monitor.c

···
 
 #include <unistd.h>
 #include <stdlib.h>
+#include <dirent.h>
 #include <stdbool.h>
 #include <stdio.h>
 #include <errno.h>
···
 	printf("\n");
 }
 
+/* Enable or disable events in sysfs if the knob is available */
+static void enable_events(char *dev_dir, int enable)
+{
+	const struct dirent *ent;
+	char evdir[256];
+	int ret;
+	DIR *dp;
+
+	snprintf(evdir, sizeof(evdir), FORMAT_EVENTS_DIR, dev_dir);
+	evdir[sizeof(evdir)-1] = '\0';
+
+	dp = opendir(evdir);
+	if (!dp) {
+		fprintf(stderr, "Enabling/disabling events: can't open %s\n",
+			evdir);
+		return;
+	}
+
+	while (ent = readdir(dp), ent) {
+		if (iioutils_check_suffix(ent->d_name, "_en")) {
+			printf("%sabling: %s\n",
+			       enable ? "En" : "Dis",
+			       ent->d_name);
+			ret = write_sysfs_int(ent->d_name, evdir,
+					      enable);
+			if (ret < 0)
+				fprintf(stderr, "Failed to enable/disable %s\n",
+					ent->d_name);
+		}
+	}
+
+	if (closedir(dp) == -1) {
+		perror("Enabling/disabling channels: "
+		       "Failed to close directory");
+		return;
+	}
+}
+
 int main(int argc, char **argv)
 {
 	struct iio_event_data event;
 	const char *device_name;
+	char *dev_dir_name = NULL;
 	char *chrdev_name;
 	int ret;
 	int dev_num;
 	int fd, event_fd;
+	bool all_events = false;
 
-	if (argc <= 1) {
-		fprintf(stderr, "Usage: %s <device_name>\n", argv[0]);
+	if (argc == 2) {
+		device_name = argv[1];
+	} else if (argc == 3) {
+		device_name = argv[2];
+		if (!strcmp(argv[1], "-a"))
+			all_events = true;
+	} else {
+		fprintf(stderr,
+			"Usage: iio_event_monitor [options] <device_name>\n"
+			"Listen and display events from IIO devices\n"
+			"  -a         Auto-activate all available events\n");
 		return -1;
 	}
-
-	device_name = argv[1];
 
 	dev_num = find_type_by_name(device_name, "iio:device");
 	if (dev_num >= 0) {
 		printf("Found IIO device with name %s with device number %d\n",
 		       device_name, dev_num);
 		ret = asprintf(&chrdev_name, "/dev/iio:device%d", dev_num);
+		if (ret < 0)
+			return -ENOMEM;
+		/* Look up sysfs dir as well if we can */
+		ret = asprintf(&dev_dir_name, "%siio:device%d", iio_dir, dev_num);
 		if (ret < 0)
 			return -ENOMEM;
 	} else {
···
 		if (!chrdev_name)
 			return -ENOMEM;
 	}
+
+	if (all_events && dev_dir_name)
+		enable_events(dev_dir_name, 1);
 
 	fd = open(chrdev_name, 0);
 	if (fd == -1) {
···
 		perror("Failed to close event file");
 
 error_free_chrdev_name:
+	/* Disable events after use */
+	if (all_events && dev_dir_name)
+		enable_events(dev_dir_name, 0);
+
 	free(chrdev_name);
 
 	return ret;

tools/iio/iio_utils.h

···
 #define IIO_MAX_NAME_LENGTH 64
 
 #define FORMAT_SCAN_ELEMENTS_DIR "%s/buffer%d"
+#define FORMAT_EVENTS_DIR "%s/events"
 #define FORMAT_TYPE_FILE "%s_type"
 
 #define ARRAY_SIZE(arr) (sizeof(arr) / sizeof(arr[0]))