linux-kernel - [PATCH] of/platform: Avoid compilation warning

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Date:   Thu, 14 May 2020 19:07:07 +0200
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        <devicetree@...r.kernel.org>
Cc:     Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        <linux-kernel@...r.kernel.org>,
        Miquel Raynal <miquel.raynal@...tlin.com>
Subject: [PATCH] of/platform: Avoid compilation warning

The of_find_device_by_node() helper has its dummy counterpart for when
CONFIG_OF is not enabled. However, it is clearly stated in the kernel
documentation that it "takes a reference to the embedded struct device
which needs to be dropped after use". Which means the of_dev_put()
helper might have to be called afterwards. Unfortunately, there is no
of_dev_put() dummy function if OF_CONFIG is not enabled which seems
odd in this case. The of_dev_put() helper is pretty simple, it just
checks the validity of the single argument and calls put_device() on
it. One can just call put_device() directly to avoid any build issue
but I find much more accurate in this case to create the dummy
helper.

With this helper, a file using of_find_device_by_node() can also call
of_dev_put() without triggering the following:

error: implicit declaration of function ‘of_dev_put’; did you mean ‘of_node_put’? [-Werror=implicit-function-declaration]

Signed-off-by: Miquel Raynal <miquel.raynal@...tlin.com>
---
 include/linux/of_platform.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/include/linux/of_platform.h b/include/linux/of_platform.h
index 84a966623e78..84d9e60e517e 100644
--- a/include/linux/of_platform.h
+++ b/include/linux/of_platform.h
@@ -54,11 +54,13 @@ extern struct platform_device *of_device_alloc(struct device_node *np,
 					 struct device *parent);
 #ifdef CONFIG_OF
 extern struct platform_device *of_find_device_by_node(struct device_node *np);
+extern void of_dev_put(struct platform_device *dev);
 #else
 static inline struct platform_device *of_find_device_by_node(struct device_node *np)
 {
 	return NULL;
 }
+static inline void of_dev_put(struct platform_device *dev) { }
 #endif

 /* Platform devices and busses creation */
-- 
2.20.1