linux-kernel - [PATCH v1 1/2] driver core: Introduce device_find_first

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Message-Id: <20220607202058.8304-1-andriy.shevchenko@linux.intel.com>
Date:   Tue,  7 Jun 2022 23:20:57 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Mark Brown <broonie@...nel.org>, linux-kernel@...r.kernel.org,
        linux-spi@...r.kernel.org
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Subject: [PATCH v1 1/2] driver core: Introduce device_find_first_child() helper

There are several places in the kernel where this kind of functionality is
being used. Provide a generic helper for such cases.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
---
 drivers/base/core.c    | 24 ++++++++++++++++++++++++
 include/linux/device.h |  1 +
 2 files changed, 25 insertions(+)

diff --git a/drivers/base/core.c b/drivers/base/core.c
index 7cd789c4985d..972bfe975cd0 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -3832,6 +3832,30 @@ struct device *device_find_child_by_name(struct device *parent,
 }
 EXPORT_SYMBOL_GPL(device_find_child_by_name);
 
+/**
+ * device_find_first_child - device iterator for locating the fist child device.
+ * @parent: parent struct device
+ *
+ * This is similar to the device_find_child() function above, but it
+ * returns a reference to the first child device.
+ *
+ * NOTE: you will need to drop the reference with put_device() after use.
+ */
+struct device *device_find_first_child(struct device *parent)
+{
+	struct klist_iter i;
+	struct device *child;
+
+	if (!parent)
+		return NULL;
+
+	klist_iter_init(&parent->p->klist_children, &i);
+	child = get_device(next_device(&i));
+	klist_iter_exit(&i);
+	return child;
+}
+EXPORT_SYMBOL_GPL(device_find_first_child);
+
 int __init devices_init(void)
 {
 	devices_kset = kset_create_and_add("devices", &device_uevent_ops, NULL);
diff --git a/include/linux/device.h b/include/linux/device.h
index dc941997795c..20171a4358df 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -905,6 +905,7 @@ struct device *device_find_child(struct device *dev, void *data,
 				 int (*match)(struct device *dev, void *data));
 struct device *device_find_child_by_name(struct device *parent,
 					 const char *name);
+struct device *device_find_first_child(struct device *parent);
 int device_rename(struct device *dev, const char *new_name);
 int device_move(struct device *dev, struct device *new_parent,
 		enum dpm_order dpm_order);
-- 
2.35.1