linux-kernel - [PATCH v3 1/4] device property: document device_for_each_child

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Message-Id: <20240805-device_for_each_child_node-available-v3-1-48243a4aa5c0@gmail.com>
Date: Mon, 05 Aug 2024 16:49:44 +0200
From: Javier Carrasco <javier.carrasco.cruz@...il.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
 "Rafael J. Wysocki" <rafael@...nel.org>, 
 Andy Shevchenko <andriy.shevchenko@...ux.intel.com>, 
 Jonathan Cameron <jic23@...nel.org>, Rob Herring <robh@...nel.org>, 
 Daniel Scally <djrscally@...il.com>, 
 Heikki Krogerus <heikki.krogerus@...ux.intel.com>, 
 Sakari Ailus <sakari.ailus@...ux.intel.com>, 
 Jean Delvare <jdelvare@...e.com>, Guenter Roeck <linux@...ck-us.net>, 
 Pavel Machek <pavel@....cz>, Lee Jones <lee@...nel.org>, 
 Marcin Wojtas <marcin.s.wojtas@...il.com>, 
 Russell King <linux@...linux.org.uk>, 
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
 Andreas Kemnade <andreas@...nade.info>
Cc: linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org, 
 linux-hwmon@...r.kernel.org, linux-leds@...r.kernel.org, 
 netdev@...r.kernel.org, Javier Carrasco <javier.carrasco.cruz@...il.com>, 
 Jonathan Cameron <Jonathan.Cameron@...wei.com>
Subject: [PATCH v3 1/4] device property: document
 device_for_each_child_node macro

There have been some misconceptions about this macro, which iterates
over available child nodes from different backends.

As that is not obvious by its name, some users have opted for the
`fwnode_for_each_available_child_node()` macro instead.
That requires an unnecessary, explicit access to the fwnode member
of the device structure.

Passing the device to `device_for_each_child_node()` is shorter,
reflects more clearly the nature of the child nodes, and renders the
same result.

In general, `fwnode_for_each_available_child_node()` should be used
whenever the parent node of the children to iterate over is a firmware
node, and not the device itself.

Document the `device_for_each_child node(dev, child)` macro to clarify
its functionality.

Suggested-by: Jonathan Cameron <jic23@...nel.org>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
Signed-off-by: Javier Carrasco <javier.carrasco.cruz@...il.com>
---
 include/linux/property.h | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/include/linux/property.h b/include/linux/property.h
index 61fc20e5f81f..da8f1208de38 100644
--- a/include/linux/property.h
+++ b/include/linux/property.h
@@ -171,6 +171,16 @@ struct fwnode_handle *fwnode_get_next_available_child_node(
 struct fwnode_handle *device_get_next_child_node(const struct device *dev,
 						 struct fwnode_handle *child);

+/**
+ * device_for_each_child_node - iterate over available child nodes of a device
+ * @dev: Pointer to the struct device
+ * @child: Pointer to an available child node in each loop iteration
+ *
+ * Unavailable nodes are skipped i.e. this macro is implicitly _available_.
+ * The reference to the child node must be dropped on early exits.
+ * See fwnode_handle_put().
+ * For a scoped version of this macro, use device_for_each_child_node_scoped().
+ */
 #define device_for_each_child_node(dev, child)				\
 	for (child = device_get_next_child_node(dev, NULL); child;	\
 	     child = device_get_next_child_node(dev, child))

-- 
2.43.0