+/*
+ * acpi_companion_match() - Can we match via ACPI companion device
+ * @dev: Device in question
+ *
+ * Check if the given device has an ACPI companion and if that companion has
+ * a valid list of PNP IDs, and if the device is the first (primary) physical
+ * device associated with it.
+ *
+ * If multiple physical devices are attached to a single ACPI companion, we need
+ * to be careful. The usage scenario for this kind of relationship is that all
+ * of the physical devices in question use resources provided by the ACPI
+ * companion. A typical case is an MFD device where all the sub-devices share
+ * the parent's ACPI companion. In such cases we can only allow the primary
+ * (first) physical device to be matched with the help of the companion's PNP
+ * IDs.
+ *
+ * Additional physical devices sharing the ACPI companion can still use
+ * resources available from it but they will be matched normally using functions
+ * provided by their bus types (and analogously for their modalias).
+ */
+static bool acpi_companion_match(const struct device *dev)
+{
+ struct acpi_device *adev;
+ bool ret;
+
+ adev = ACPI_COMPANION(dev);
+ if (!adev)
+ return false;
+
+ if (list_empty(&adev->pnp.ids))
+ return false;
+
+ mutex_lock(&adev->physical_node_lock);
+ if (list_empty(&adev->physical_node_list)) {
+ ret = false;
+ } else {
+ const struct acpi_device_physical_node *node;
+
+ node = list_first_entry(&adev->physical_node_list,
+ struct acpi_device_physical_node, node);
+ ret = node->dev == dev;
+ }
+ mutex_unlock(&adev->physical_node_lock);
+
+ return ret;
+}
+