iio: add child nodes support in iio backend framework

Add an API to support IIO generic channels binding:
http://devicetree.org/schemas/iio/adc/adc.yaml#
This new API is needed, as generic channel DT node isn't populated as a
device.
Add devm_iio_backend_fwnode_get() to allow an IIO device backend
consumer to reference backend phandles in its child nodes.
Signed-off-by: Olivier Moysan <olivier.moysan@foss.st.com>
Reviewed-by: Nuno Sa <nuno.sa@analog.com>
Link: https://patch.msgid.link/20240730084640.1307938-4-olivier.moysan@foss.st.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/industrialio-backend.c

@@ -718,19 +718,10 @@ static int __devm_iio_backend_get(struct device *dev, struct iio_backend *back)
 	return 0;
 }
 
-/**
- * devm_iio_backend_get - Device managed backend device get
- * @dev: Consumer device for the backend
- * @name: Backend name
- *
- * Get's the backend associated with @dev.
- *
- * RETURNS:
- * A backend pointer, negative error pointer otherwise.
- */
-struct iio_backend *devm_iio_backend_get(struct device *dev, const char *name)
+static struct iio_backend *__devm_iio_backend_fwnode_get(struct device *dev, const char *name,
+							 struct fwnode_handle *fwnode)
 {
-	struct fwnode_handle *fwnode;
+	struct fwnode_handle *fwnode_back;
 	struct iio_backend *back;
 	unsigned int index;
 	int ret;
@@ -745,17 +736,17 @@ struct iio_backend *devm_iio_backend_get(struct device *dev, const char *name)
 		index = 0;
 	}
 
-	fwnode = fwnode_find_reference(dev_fwnode(dev), "io-backends", index);
+	fwnode_back = fwnode_find_reference(fwnode, "io-backends", index);
 	if (IS_ERR(fwnode))
 		return dev_err_cast_probe(dev, fwnode,
 					  "Cannot get Firmware reference\n");
 
 	guard(mutex)(&iio_back_lock);
 	list_for_each_entry(back, &iio_back_list, entry) {
-		if (!device_match_fwnode(back->dev, fwnode))
+		if (!device_match_fwnode(back->dev, fwnode_back))
 			continue;
 
-		fwnode_handle_put(fwnode);
+		fwnode_handle_put(fwnode_back);
 		ret = __devm_iio_backend_get(dev, back);
 		if (ret)
 			return ERR_PTR(ret);
@@ -766,11 +757,45 @@ struct iio_backend *devm_iio_backend_get(struct device *dev, const char *name)
 		return back;
 	}
 
-	fwnode_handle_put(fwnode);
+	fwnode_handle_put(fwnode_back);
 	return ERR_PTR(-EPROBE_DEFER);
 }
+
+/**
+ * devm_iio_backend_get - Device managed backend device get
+ * @dev: Consumer device for the backend
+ * @name: Backend name
+ *
+ * Get's the backend associated with @dev.
+ *
+ * RETURNS:
+ * A backend pointer, negative error pointer otherwise.
+ */
+struct iio_backend *devm_iio_backend_get(struct device *dev, const char *name)
+{
+	return __devm_iio_backend_fwnode_get(dev, name, dev_fwnode(dev));
+}
 EXPORT_SYMBOL_NS_GPL(devm_iio_backend_get, IIO_BACKEND);
 
+/**
+ * devm_iio_backend_fwnode_get - Device managed backend firmware node get
+ * @dev: Consumer device for the backend
+ * @name: Backend name
+ * @fwnode: Firmware node of the backend consumer
+ *
+ * Get's the backend associated with a firmware node.
+ *
+ * RETURNS:
+ * A backend pointer, negative error pointer otherwise.
+ */
+struct iio_backend *devm_iio_backend_fwnode_get(struct device *dev,
+						const char *name,
+						struct fwnode_handle *fwnode)
+{
+	return __devm_iio_backend_fwnode_get(dev, name, fwnode);
+}
+EXPORT_SYMBOL_NS_GPL(devm_iio_backend_fwnode_get, IIO_BACKEND);
+
 /**
  * __devm_iio_backend_get_from_fwnode_lookup - Device managed fwnode backend device get
  * @dev: Consumer device for the backend

include/linux/iio/backend.h

@@ -176,6 +176,9 @@ int iio_backend_extend_chan_spec(struct iio_backend *back,
 				 struct iio_chan_spec *chan);
 void *iio_backend_get_priv(const struct iio_backend *conv);
 struct iio_backend *devm_iio_backend_get(struct device *dev, const char *name);
+struct iio_backend *devm_iio_backend_fwnode_get(struct device *dev,
+						const char *name,
+						struct fwnode_handle *fwnode);
 struct iio_backend *
 __devm_iio_backend_get_from_fwnode_lookup(struct device *dev,
 					  struct fwnode_handle *fwnode);