linux-kernel - [PATCH v3] staging: vme_user: simplify bus number allocation using ffz()

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Message-ID: <20251210094207.33671-2-dharanitharan725@gmail.com>
Date: Wed, 10 Dec 2025 09:42:08 +0000
From: Dharanitharan R <dharanitharan725@...il.com>
To: gregkh@...uxfoundation.org
Cc: linux-staging@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	david.laight.linux@...il.com,
	dharanitharan725@...il.com
Subject: [PATCH v3] staging: vme_user: simplify bus number allocation using ffz()

David Laight pointed out that the loop in vme_register_bridge()
is effectively searching for the first zero bit in vme_bus_numbers.
Add a check for vme_bus_numbers == ~0UL before calling ffz().

Replace the manual loop with ffz() and use BIT(n) for consistency.

Suggested-by: David Laight <david.laight.linux@...il.com>
Signed-off-by: Dharanitharan R <dharanitharan725@...il.com>
---
 drivers/staging/vme_user/vme.c | 15 +++++++++++++----------
 1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/drivers/staging/vme_user/vme.c b/drivers/staging/vme_user/vme.c
index 2095de72596a..45381e677475 100644
--- a/drivers/staging/vme_user/vme.c
+++ b/drivers/staging/vme_user/vme.c
@@ -1765,16 +1765,19 @@ int vme_register_bridge(struct vme_bridge *bridge)
 	int ret = -1;
 
 	mutex_lock(&vme_buses_lock);
-	for (i = 0; i < sizeof(vme_bus_numbers) * 8; i++){
-		if ((vme_bus_numbers & (1 << i)) == 0) {
-			vme_bus_numbers |= (1 << i);
-			bridge->num = i;
-			INIT_LIST_HEAD(&bridge->devices);
-			list_add_tail(&bridge->bus_list, &vme_bus_list);
-			ret = 0;
-			break;
-		}
+	/* Ensure we have a free slot before using ffz() */
+	if (vme_bus_numbers == ~0UL)
+		goto out;   /* No free bus number */
+
+	/* Find the first clear bit */
+	i = ffz(vme_bus_numbers);
+
+	vme_bus_numbers |= BIT(i);
+	bridge->num = i;
+	INIT_LIST_HEAD(&bridge->devices);
+	list_add_tail(&bridge->bus_list, &vme_bus_list);
+	ret = 0;
+
+out:
 	mutex_unlock(&vme_buses_lock);
 
 	return ret;
@@ -1787,7 +1790,7 @@ void vme_unregister_bridge(struct vme_bridge *bridge)
 	struct vme_dev *tmp;
 
 	mutex_lock(&vme_buses_lock);
-	vme_bus_numbers &= ~(1 << bridge->num);
+	vme_bus_numbers &= ~BIT(bridge->num);
 	list_for_each_entry_safe(vdev, tmp, &bridge->devices, bridge_list) {
 		list_del(&vdev->drv_list);
 		list_del(&vdev->bridge_list);
-- 
2.43.0