iio-buffer-utils: Make sure sampling_frequency is 10Hz or more

Add a new iio_fixup_sampling_frequency() helper to iio-buffer-utils.c and
call this for all iio devices. iio_fixup_sampling_frequency() makes sure that
devices with *sampling_frequency attributes are sampling at 10Hz or more.

This fixes 2 problems:

1) Some buffered devices default their sampling_frequency to 0Hz and then
never produce any readings. This fixes e.g. the sensors on Asus T100HA
2-in-1s not working.

2) Some polled devices default to 1Hz and wait for a fresh sample before
returning from sysfs *_raw reads, blocking all of iio-sensor-proxy for
multiple seconds, this fixes e.g. rotation being detected up to 10 seconds
later then the actual rotating of the device on a Lenovo Miix 320.

src/drv-iio-poll-accel.c

@@ -7,6 +7,7 @@
  */
 
 #include "drivers.h"
+#include "iio-buffer-utils.h"
 #include "accel-mount-matrix.h"
 
 #include <fcntl.h>
@@ -119,6 +120,8 @@ iio_poll_accel_open (GUdevDevice        *device,
 {
 	const char *mount_matrix;
 
+	iio_fixup_sampling_frequency (device);
+
 	drv_data = g_new0 (DrvData, 1);
 	drv_data->dev = g_object_ref (device);
 	drv_data->name = g_udev_device_get_sysfs_attr (device, "name");

src/drv-iio-poll-light.c

@@ -7,6 +7,7 @@
  */
 
 #include "drivers.h"
+#include "iio-buffer-utils.h"
 
 #include <fcntl.h>
 #include <unistd.h>
@@ -114,6 +115,8 @@ iio_poll_light_open (GUdevDevice        *device,
 		     ReadingsUpdateFunc  callback_func,
 		     gpointer            user_data)
 {
+	iio_fixup_sampling_frequency (device);
+
 	drv_data = g_new0 (DrvData, 1);
 	drv_data->callback_func = callback_func;
 	drv_data->user_data = user_data;

src/iio-buffer-utils.c

@@ -17,6 +17,8 @@
 #include <errno.h>
 #include <stdio.h>
 
+#define IIO_MIN_SAMPLING_FREQUENCY	10 /* Hz */
+
 /**
  * iio_channel_info - information about a given channel
  * @name: channel name
@@ -568,6 +570,51 @@ process_scan_1 (char              *data,
 		g_warning ("IIO channel '%s' could not be found", ch_name);
 }
 
+/**
+ * iio_fixup_sampling_frequency: Fixup devices *sampling_frequency attributes
+ * @dev: the IIO device to fix the sampling frequencies for
+ *
+ * Make sure devices with *sampling_frequency attributes are sampling at
+ * 10Hz or more. This fixes 2 problems:
+ * 1) Some buffered devices default their sampling_frequency to 0Hz and then
+ * never produce any readings.
+ * 2) Some polled devices default to 1Hz and wait for a fresh sample before
+ * returning from sysfs *_raw reads, blocking all of iio-sensor-proxy for
+ * multiple seconds
+ **/
+gboolean
+iio_fixup_sampling_frequency (GUdevDevice *dev)
+{
+	GDir *dir;
+	const char *device_dir;
+	const char *name;
+	GError *error = NULL;
+	double sample_freq;
+
+	device_dir = g_udev_device_get_sysfs_path (dev);
+	dir = g_dir_open (g_udev_device_get_sysfs_path (dev), 0, &error);
+	if (!dir) {
+		g_warning ("Failed to open directory '%s': %s", device_dir, error->message);
+		g_error_free (error);
+		return FALSE;
+	}
+
+	while ((name = g_dir_read_name (dir))) {
+		if (g_str_has_suffix (name, "sampling_frequency") == FALSE)
+			continue;
+
+		sample_freq = g_udev_device_get_sysfs_attr_as_double (dev, name);
+		if (sample_freq >= IIO_MIN_SAMPLING_FREQUENCY)
+			continue; /* Continue with pre-set sample freq. */
+
+		/* Sample freq too low, set it to 10Hz */
+		if (write_sysfs_int (name, device_dir, IIO_MIN_SAMPLING_FREQUENCY) < 0)
+			g_warning ("Could not fix sample-freq for %s/%s", device_dir, name);
+	}
+	g_dir_close (dir);
+	return TRUE;
+}
+
 /**
  * enable_sensors: enable all the sensors in a device
  * @device_dir: the IIO device directory in sysfs
@@ -719,7 +766,8 @@ buffer_drv_data_new (GUdevDevice *device,
 	buffer_data->trigger_name = g_strdup (trigger_name);
 	buffer_data->device = g_object_ref (device);
 
-	if (!enable_sensors (device, 1) ||
+	if (!iio_fixup_sampling_frequency (device) ||
+	    !enable_sensors (device, 1) ||
 	    !enable_trigger (buffer_data) ||
 	    !enable_ring_buffer (buffer_data) ||
 	    !build_channels (buffer_data)) {

src/iio-buffer-utils.h

@@ -35,6 +35,7 @@ void process_scan_1                    (char              *data,
 				        int               *ch_val,
 				        gdouble           *ch_scale,
 				        gboolean          *ch_present);
+gboolean iio_fixup_sampling_frequency  (GUdevDevice *dev);
 
 void           buffer_drv_data_free    (BufferDrvData *buffer_data);
 BufferDrvData *buffer_drv_data_new     (GUdevDevice *device,