linux-kernel - [PATCH v2] driver core: auxiliary bus: Optimize logic of auxiliary_match

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Message-Id: <20250903-fix_auxbus-v2-1-3eae8374fd65@oss.qualcomm.com>
Date: Wed, 03 Sep 2025 19:37:22 +0800
From: Zijun Hu <zijun_hu@...oud.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
 Dave Ertman <david.m.ertman@...el.com>, Ira Weiny <ira.weiny@...el.com>, 
 Leon Romanovsky <leon@...nel.org>, "Rafael J. Wysocki" <rafael@...nel.org>, 
 Danilo Krummrich <dakr@...nel.org>
Cc: Zijun Hu <zijun_hu@...oud.com>, linux-kernel@...r.kernel.org, 
 Zijun Hu <zijun.hu@....qualcomm.com>
Subject: [PATCH v2] driver core: auxiliary bus: Optimize logic of
 auxiliary_match_id()

From: Zijun Hu <zijun.hu@....qualcomm.com>

auxiliary_match_id() repeatedly calculates variable @match_size in the
for loop, however, the variable is fixed actually, so it is enough to
only calculate the variable once.

Besides, the function should return directly if name of the @auxdev
does not include '.', but it still iterates over the ID table.

Additionally, statement 'dev_name(&auxdev->dev)' is fixed, but may be
evaluated more than 3 times.

Optimize logic of the function by:
- Move the logic calculating the variable out of the for loop
- Return NULL directly if @p == NULL
- Give the statement an dedicated local variable @auxdev_name

Signed-off-by: Zijun Hu <zijun.hu@....qualcomm.com>
---
Changes in v2:
- Give statement 'dev_name(&auxdev->dev)' a dedicated local variable
- Correct tile and commit message
- Link to v1: https://lore.kernel.org/r/20250902-fix_auxbus-v1-1-9ba6d8aff027@oss.qualcomm.com
---
 drivers/base/auxiliary.c | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/drivers/base/auxiliary.c b/drivers/base/auxiliary.c
index 12ffdd8437567f282374bbf3775d9de7ca0dc4c7..ed2537cf3b048149e784e5a582631db549050734 100644
--- a/drivers/base/auxiliary.c
+++ b/drivers/base/auxiliary.c
@@ -171,17 +171,18 @@
 static const struct auxiliary_device_id *auxiliary_match_id(const struct auxiliary_device_id *id,
 							    const struct auxiliary_device *auxdev)
 {
-	for (; id->name[0]; id++) {
-		const char *p = strrchr(dev_name(&auxdev->dev), '.');
-		int match_size;
+	const char *auxdev_name = dev_name(&auxdev->dev);
+	const char *p = strrchr(auxdev_name, '.');
+	int match_size;

-		if (!p)
-			continue;
-		match_size = p - dev_name(&auxdev->dev);
+	if (!p)
+		return NULL;
+	match_size = p - auxdev_name;

+	for (; id->name[0]; id++) {
 		/* use dev_name(&auxdev->dev) prefix before last '.' char to match to */
 		if (strlen(id->name) == match_size &&
-		    !strncmp(dev_name(&auxdev->dev), id->name, match_size))
+		    !strncmp(auxdev_name, id->name, match_size))
 			return id;
 	}
 	return NULL;

---
base-commit: 1b237f190eb3d36f52dffe07a40b5eb210280e00
change-id: 20250902-fix_auxbus-76bec91376db

Best regards,
-- 
Zijun Hu <zijun.hu@....qualcomm.com>