HID: hid-sensor-hub: don't use stale platform-data on remove

The hid-sensor-hub creates the individual device structs and transfers them
to the created mfd platform-devices via the platform_data in the mfd_cell.

Before e651a1da442a ("HID: hid-sensor-hub: Allow parallel synchronous reads")
the sensor-hub was managing access centrally, with one "completion" in the
hub's data structure, which needed to be finished on removal at the latest.

The mentioned commit then moved this central management to each hid sensor
device, resulting on a completion in each struct hid_sensor_hub_device.
The remove procedure was adapted to go through all sensor devices and
finish any pending "completion".

What this didn't take into account was, platform_device_add_data() that is
used by mfd_add{_hotplug}_devices() does a kmemdup on the submitted
platform-data. So the data the platform-device gets is a copy of the
original data, meaning that the device worked on a different completion
than what sensor_hub_remove() currently wants to access.

To fix that, use device_for_each_child() to go through each child-device
similar to how mfd_remove_devices() unregisters the devices later and
with that get the live platform_data to finalize the correct completion.

Fixes: e651a1da442a ("HID: hid-sensor-hub: Allow parallel synchronous reads")
Cc: [e-mail]
Signed-off-by: Heiko Stuebner <[e-mail]>
Acked-by: Benjamin Tissoires <[e-mail]>
Acked-by: Srinivas Pandruvada <[e-mail]>
Acked-by: Jiri Kosina <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Lee Jones <[e-mail]>

drivers/hid/hid-sensor-hub.c

···
 	return ret;
 }
 
+static int sensor_hub_finalize_pending_fn(struct device *dev, void *data)
+{
+	struct hid_sensor_hub_device *hsdev = dev->platform_data;
+
+	if (hsdev->pending.status)
+		complete(&hsdev->pending.ready);
+
+	return 0;
+}
+
 static void sensor_hub_remove(struct hid_device *hdev)
 {
 	struct sensor_hub_data *data = hid_get_drvdata(hdev);
 	unsigned long flags;
-	int i;
 
 	hid_dbg(hdev, " hardware removed\n");
 	hid_hw_close(hdev);
 	hid_hw_stop(hdev);
+
 	spin_lock_irqsave(&data->lock, flags);
-	for (i = 0; i < data->hid_sensor_client_cnt; ++i) {
-		struct hid_sensor_hub_device *hsdev =
-			data->hid_sensor_hub_client_devs[i].platform_data;
-		if (hsdev->pending.status)
-			complete(&hsdev->pending.ready);
-	}
+	device_for_each_child(&hdev->dev, NULL,
+			      sensor_hub_finalize_pending_fn);
 	spin_unlock_irqrestore(&data->lock, flags);
+
 	mfd_remove_devices(&hdev->dev);
 	mutex_destroy(&data->mutex);
 }