From: "Sicelo A. Mhlongo" <absicsz@gmail.com>
Date: Mon, 26 May 2025 09:11:59 +0200
Subject: iio-buffer: attempt to read from buffer during sensor discovery

The kernel drivers for some sensors report support for buffer mode, and allow
the buffer to be enabled, but never return any data in the buffer. Since
59c29aca616f ("drivers: accel: Remove trigger requirement on
iio-buffer-accel"), these sensors fail silently. iio-sensor-proxy must use the
polling method on these sensors.

To achieve this, during sensor discovery, enable the sensor in buffer mode,
then attempt to read data off the buffer. Modify tests in order for the data
file to be opened before startDaemon() is called, since this is now necessary
for sensor discovery.

Fixes: #411 [0]
[0] https://gitlab.freedesktop.org/hadess/iio-sensor-proxy/-/issues/411
---
 src/drv-iio-buffer-accel.c   | 20 +++++++++++++++++++-
 src/drv-iio-buffer-compass.c | 24 +++++++++++++++++++++---
 src/drv-iio-buffer-light.c   | 24 +++++++++++++++++++++---
 src/iio-buffer-utils.c       | 30 ++++++++++++++++++++----------
 src/iio-buffer-utils.h       |  2 +-
 tests/integration-test.py    | 16 ++++++++++++++--
 6 files changed, 96 insertions(+), 20 deletions(-)

diff --git a/src/drv-iio-buffer-accel.c b/src/drv-iio-buffer-accel.c
index 06db1aa..5900ac5 100644
--- a/src/drv-iio-buffer-accel.c
+++ b/src/drv-iio-buffer-accel.c
@@ -191,12 +191,30 @@ iio_buffer_accel_close (SensorDevice *sensor_device)
 static gboolean
 iio_buffer_accel_discover (GUdevDevice *device)
 {
+	SensorDevice *sensor_device;
+	DrvData *drv_data;
+	gboolean buffer_usable = FALSE;
+
 	if (!drv_check_udev_sensor_type (device, "iio-buffer-accel", NULL))
 		return FALSE;
 
-	if (!is_buffer_usable (device))
+	sensor_device = iio_buffer_accel_open (device);
+	if (!sensor_device)
 		return FALSE;
 
+	/* Attempt to read from the sensor */
+	drv_data = (DrvData *) sensor_device->priv;
+	enable_ring_buffer (drv_data->buffer_data);
+
+	buffer_usable = is_buffer_usable(drv_data->dev_path);
+
+	/* Close the sensor until it has been claimed */
+	disable_ring_buffer (drv_data->buffer_data);
+	iio_buffer_accel_close (sensor_device);
+
+	if (!buffer_usable)
+		 return FALSE;
+
 	g_debug ("Found IIO buffer accelerometer at %s", g_udev_device_get_sysfs_path (device));
 	return TRUE;
 }
diff --git a/src/drv-iio-buffer-compass.c b/src/drv-iio-buffer-compass.c
index 2ae0ccd..4638134 100644
--- a/src/drv-iio-buffer-compass.c
+++ b/src/drv-iio-buffer-compass.c
@@ -20,7 +20,7 @@ typedef struct {
 	guint               timeout_id;
 
 	GUdevDevice        *dev;
-	const char         *dev_path;
+	char               *dev_path;
 	int                 device_id;
 	BufferDrvData      *buffer_data;
 } DrvData;
@@ -125,7 +125,7 @@ iio_buffer_compass_open (GUdevDevice *device)
 	drv_data = (DrvData *) sensor_device->priv;
 	drv_data->dev = g_object_ref (device);
 	drv_data->buffer_data = buffer_data;
-	drv_data->dev_path = g_udev_device_get_device_file (device);
+	drv_data->dev_path = get_device_file (device);
 
 	return sensor_device;
 }
@@ -170,10 +170,28 @@ iio_buffer_compass_close (SensorDevice *sensor_device)
 static gboolean
 iio_buffer_compass_discover (GUdevDevice *device)
 {
+	SensorDevice *sensor_device;
+	DrvData *drv_data;
+	gboolean buffer_usable = FALSE;
+
 	if (!drv_check_udev_sensor_type (device, "iio-buffer-compass", NULL))
 		return FALSE;
 
-	if (!is_buffer_usable (device))
+	sensor_device = iio_buffer_compass_open (device);
+	if (!sensor_device)
+		return FALSE;
+
+	/* Attempt to read from the sensor */
+	drv_data = (DrvData *) sensor_device->priv;
+	enable_ring_buffer (drv_data->buffer_data);
+
+	buffer_usable = is_buffer_usable(drv_data->dev_path);
+
+	/* Close the sensor until it has been claimed */
+	disable_ring_buffer (drv_data->buffer_data);
+	iio_buffer_compass_close (sensor_device);
+
+	if (!buffer_usable)
 		return FALSE;
 
 	g_debug ("Found IIO buffer compass at %s", g_udev_device_get_sysfs_path (device));
diff --git a/src/drv-iio-buffer-light.c b/src/drv-iio-buffer-light.c
index 2a524c6..7a423c5 100644
--- a/src/drv-iio-buffer-light.c
+++ b/src/drv-iio-buffer-light.c
@@ -20,7 +20,7 @@ typedef struct {
 	guint              timeout_id;
 
 	GUdevDevice *dev;
-	const char *dev_path;
+	char *dev_path;
 	int device_id;
 	BufferDrvData *buffer_data;
 } DrvData;
@@ -156,7 +156,7 @@ iio_buffer_light_open (GUdevDevice *device)
 	drv_data = (DrvData *) sensor_device->priv;
 	drv_data->dev = g_object_ref (device);
 	drv_data->buffer_data = buffer_data;
-	drv_data->dev_path = g_udev_device_get_device_file (device);
+	drv_data->dev_path = get_device_file (device);
 
 	return sensor_device;
 }
@@ -175,10 +175,28 @@ iio_buffer_light_close (SensorDevice *sensor_device)
 static gboolean
 iio_buffer_light_discover (GUdevDevice *device)
 {
+	SensorDevice *sensor_device;
+	DrvData *drv_data;
+	gboolean buffer_usable = FALSE;
+
 	if (!drv_check_udev_sensor_type (device, "iio-buffer-als", NULL))
 		return FALSE;
 
-	if (!is_buffer_usable (device))
+	sensor_device = iio_buffer_light_open (device);
+	if (!sensor_device)
+		return FALSE;
+
+	/* Attempt to read from the sensor */
+	drv_data = (DrvData *) sensor_device->priv;
+	enable_ring_buffer (drv_data->buffer_data);
+
+	buffer_usable = is_buffer_usable(drv_data->dev_path);
+
+	/* Close the sensor until it has been claimed */
+	disable_ring_buffer (drv_data->buffer_data);
+	iio_buffer_light_close (sensor_device);
+
+	if (!buffer_usable)
 		return FALSE;
 
 	g_debug ("Found IIO buffer ALS at %s", g_udev_device_get_sysfs_path (device));
diff --git a/src/iio-buffer-utils.c b/src/iio-buffer-utils.c
index bc74e4c..29163ee 100644
--- a/src/iio-buffer-utils.c
+++ b/src/iio-buffer-utils.c
@@ -20,6 +20,7 @@
 #include <string.h>
 #include <errno.h>
 #include <stdio.h>
+#include <glib/gstdio.h>
 
 #define IIO_MIN_SAMPLING_FREQUENCY	10 /* Hz */
 
@@ -905,19 +906,28 @@ buffer_drv_data_new (GUdevDevice *device)
 }
 
 gboolean
-is_buffer_usable (GUdevDevice *device)
+is_buffer_usable (char *path)
 {
-	g_autofree char *trigger_name = NULL;
-	BufferDrvData *buffer_data;
+	gboolean buffer_usable = FALSE;
+	g_autofd int fp = -1;
+	GPollFD fds;
 
-	/* Temporarily enable the buffer to ensure the kernel driver is buffer-capable */
-	buffer_data = buffer_drv_data_new (device);
-	if (!buffer_data)
-		return FALSE;
+	/* Attempt to read from the sensor buffer */
+	fp = g_open (path, O_RDONLY | O_NONBLOCK);
+	if (fp == -1) {
+	        g_warning ("Failed to open '%s': %s", path, g_strerror (errno));
+	} else {
+	        fds.fd = fp;
+	        fds.events = G_IO_IN | G_IO_ERR;
+	        g_poll (&fds, 1, 500);
 
-	/* Destroy buffer information until actually needed (in the .open call) */
-	g_clear_pointer (&buffer_data, buffer_drv_data_free);
-	return TRUE;
+	        if (fds.revents & G_IO_IN)
+	                buffer_usable = TRUE;
+	        else
+	                g_warning ("Buffer '%s' did not have data within 0.5s", path);
+	}
+
+	return buffer_usable;
 }
 
 IIOSensorData *
diff --git a/src/iio-buffer-utils.h b/src/iio-buffer-utils.h
index 9c5e6db..2b95625 100644
--- a/src/iio-buffer-utils.h
+++ b/src/iio-buffer-utils.h
@@ -46,4 +46,4 @@ void           buffer_drv_data_free    (BufferDrvData *buffer_data);
 BufferDrvData *buffer_drv_data_new     (GUdevDevice *device);
 void     disable_ring_buffer           (BufferDrvData *data);
 gboolean enable_ring_buffer            (BufferDrvData *data);
-gboolean is_buffer_usable              (GUdevDevice *device);
+gboolean is_buffer_usable              (char *path);
diff --git a/tests/integration-test.py b/tests/integration-test.py
index 8910539..b596eaa 100755
--- a/tests/integration-test.py
+++ b/tests/integration-test.py
@@ -555,6 +555,9 @@ class Tests(dbusmock.DBusTestCase):
             ['name', 'accel_3d-dev0'],
             []
         )
+        data = self.read_file(top_srcdir + '/tests/iio-buffer-accel-data/orientation-normal.bin')
+        with open(mock_dev_data,'wb') as mock_file:
+            mock_file.write(data)
         self.start_daemon()
         self.assertEqual(self.get_dbus_property('HasAmbientLight'), False)
         self.assertEqual(self.get_dbus_property('HasAccelerometer'), True)
@@ -566,7 +569,6 @@ class Tests(dbusmock.DBusTestCase):
         self.assertEqual(self.read_sysfs_attr(accel, 'scan_elements/in_accel_y_en'), b'1')
         self.assertEqual(self.read_sysfs_attr(accel, 'scan_elements/in_accel_z_en'), b'1')
 
-        data = self.read_file(top_srcdir + '/tests/iio-buffer-accel-data/orientation-normal.bin')
         with open(mock_dev_data,'wb') as mock_file:
             mock_file.write(data)
         self.proxy.ClaimAccelerometer()
@@ -595,6 +597,8 @@ class Tests(dbusmock.DBusTestCase):
 
     def test_driver_buffer_without_trigger(self):
         '''buffer driver picking without trigger'''
+        top_srcdir = os.getenv('top_srcdir', '.')
+        mock_dev_data = self.testbed.get_root_dir() + '/iio-dev-data.bin'
         accel = self.testbed.add_device('iio', 'iio-buffer-accel0', None,
             ['name', 'IIO Test Accelerometer',
              'buffer/enable', '0',
@@ -615,6 +619,9 @@ class Tests(dbusmock.DBusTestCase):
              'IIO_SENSOR_PROXY_TYPE', 'iio-buffer-accel']
         )
 
+        data = self.read_file(top_srcdir + '/tests/iio-buffer-accel-data/orientation-normal.bin')
+        with open(mock_dev_data,'wb') as mock_file:
+            mock_file.write(data)
         self.start_daemon()
 
         self.assertEqual(self.get_dbus_property('HasAmbientLight'), False)
@@ -696,10 +703,12 @@ class Tests(dbusmock.DBusTestCase):
         )
         env = os.environ.copy()
         env['LC_NUMERIC'] = 'fr_FR.UTF-8'
+        data = self.read_file(top_srcdir + '/tests/iio-buffer-accel-data/orientation-normal.bin')
+        with open(mock_dev_data,'wb') as mock_file:
+            mock_file.write(data)
         self.start_daemon(env=env)
 
         self.assertEqual(self.get_dbus_property('HasAccelerometer'), True)
-        data = self.read_file(top_srcdir + '/tests/iio-buffer-accel-data/orientation-normal.bin')
         with open(mock_dev_data,'wb') as mock_file:
             mock_file.write(data)
         self.proxy.ClaimAccelerometer()
@@ -742,6 +751,9 @@ class Tests(dbusmock.DBusTestCase):
         )
         env = os.environ.copy()
         env['LC_NUMERIC'] = 'fr_FR.UTF-8'
+        data = self.read_file(top_srcdir + '/tests/iio-buffer-accel-data/orientation-normal.bin')
+        with open(mock_dev_data,'wb') as mock_file:
+            mock_file.write(data)
         self.start_daemon(env=env)
 
         self.assertEqual(self.get_dbus_property('HasAccelerometer'), True)