linux-kernel - [PATCH] of: replace of_match_node() macro by a function when !CONFIG

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Message-Id: <20240708-of-match-node-v1-1-90aaa7c2d21d@bootlin.com>
Date: Mon, 08 Jul 2024 10:55:31 +0200
From: Théo Lebrun <theo.lebrun@...tlin.com>
To: Rob Herring <robh@...nel.org>, Saravana Kannan <saravanak@...gle.com>
Cc: devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, 
 Vladimir Kondratiev <vladimir.kondratiev@...ileye.com>, 
 Grégory Clement <gregory.clement@...tlin.com>, 
 Thomas Petazzoni <thomas.petazzoni@...tlin.com>, 
 Tawfik Bayouk <tawfik.bayouk@...ileye.com>, 
 Théo Lebrun <theo.lebrun@...tlin.com>
Subject: [PATCH] of: replace of_match_node() macro by a function when
 !CONFIG_OF

In the !CONFIG_OF case, replace the of_match_node() macro implementation
by a static function. This ensures drivers calling of_match_node() can
be COMPILE_TESTed.

include/linux/of.h declares of_match_node() like this:

	#ifdef CONFIG_OF
	extern const struct of_device_id *of_match_node(
		const struct of_device_id *matches, const struct device_node *node);
	#else
	#define of_match_node(_matches, _node)	NULL
	#endif

When used inside an expression, those two implementations behave truly
differently. The macro implementation has (at least) two pitfalls:

 - Arguments are removed by the preprocessor meaning they do not appear
   to the compiler. This can give "defined but not used" warnings.

 - The returned value type is (void *)
   versus (const struct of_device_id *).
   It works okay if the value is stored in a variable, thanks to C's
   implicit void pointer casting rules. It causes build errors if used
   like `of_match_data(...)->data`.

Signed-off-by: Théo Lebrun <theo.lebrun@...tlin.com>
---
 include/linux/of.h | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/include/linux/of.h b/include/linux/of.h
index a0bedd038a05..f973ae119504 100644
--- a/include/linux/of.h
+++ b/include/linux/of.h
@@ -891,7 +891,13 @@ static inline const void *of_device_get_match_data(const struct device *dev)
 }
 
 #define of_match_ptr(_ptr)	NULL
-#define of_match_node(_matches, _node)	NULL
+
+static inline const struct of_device_id *of_match_node(
+	const struct of_device_id *matches, const struct device_node *node)
+{
+	return NULL;
+}
+
 #endif /* CONFIG_OF */
 
 /* Default string compare functions, Allow arch asm/prom.h to override */

---
base-commit: 256abd8e550ce977b728be79a74e1729438b4948
change-id: 20240708-of-match-node-ad30140a0a9c

Best regards,
-- 
Théo Lebrun <theo.lebrun@...tlin.com>