linux-kernel - [PATCH v2 02/17] firmware: arm_scmi: Reduce the scope of protocols mutex

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Message-ID: <20260114114638.2290765-3-cristian.marussi@arm.com>
Date: Wed, 14 Jan 2026 11:46:06 +0000
From: Cristian Marussi <cristian.marussi@....com>
To: linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	arm-scmi@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Cc: sudeep.holla@....com,
	james.quinlan@...adcom.com,
	f.fainelli@...il.com,
	vincent.guittot@...aro.org,
	etienne.carriere@...com,
	peng.fan@....nxp.com,
	michal.simek@....com,
	dan.carpenter@...aro.org,
	d-gole@...com,
	jonathan.cameron@...wei.com,
	elif.topuz@....com,
	lukasz.luba@....com,
	philip.radford@....com,
	souvik.chakravarty@....com,
	Cristian Marussi <cristian.marussi@....com>
Subject: [PATCH v2 02/17] firmware: arm_scmi: Reduce the scope of protocols mutex

Currently the mutex dedicated to the protection of the list of registered
protocols is held during all the protocol initialization phase.

Such a wide locking region is not needed and causes problem when trying to
initialize notifications from within a protocol initialization routine.

Reduce the scope of the protocol mutex.

Signed-off-by: Cristian Marussi <cristian.marussi@....com>
---
v1-->v2
 - Fixed improper mixed usage of cleanup and goto constructs
---
 drivers/firmware/arm_scmi/driver.c | 50 ++++++++++++++----------------
 1 file changed, 24 insertions(+), 26 deletions(-)

diff --git a/drivers/firmware/arm_scmi/driver.c b/drivers/firmware/arm_scmi/driver.c
index 7e5429eff35d..b198c58da1dd 100644
--- a/drivers/firmware/arm_scmi/driver.c
+++ b/drivers/firmware/arm_scmi/driver.c
@@ -17,6 +17,7 @@
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
 #include <linux/bitmap.h>
+#include <linux/cleanup.h>
 #include <linux/debugfs.h>
 #include <linux/device.h>
 #include <linux/export.h>
@@ -2123,7 +2124,6 @@ static int scmi_protocol_version_negotiate(struct scmi_protocol_handle *ph)
  * all resources management is handled via a dedicated per-protocol devres
  * group.
  *
- * Context: Assumes to be called with @protocols_mtx already acquired.
  * Return: A reference to a freshly allocated and initialized protocol instance
  *	   or ERR_PTR on failure. On failure the @proto reference is at first
  *	   put using @scmi_protocol_put() before releasing all the devres group.
@@ -2162,8 +2162,10 @@ scmi_alloc_init_protocol_instance(struct scmi_info *info,
 	if (ret)
 		goto clean;
 
-	ret = idr_alloc(&info->protocols, pi, proto->id, proto->id + 1,
-			GFP_KERNEL);
+	/* Finally register the initialized protocol */
+	mutex_lock(&info->protocols_mtx);
+	ret = idr_alloc(&info->protocols, pi, proto->id, proto->id + 1, GFP_KERNEL);
+	mutex_unlock(&info->protocols_mtx);
 	if (ret != proto->id)
 		goto clean;
 
@@ -2226,27 +2228,25 @@ scmi_alloc_init_protocol_instance(struct scmi_info *info,
 static struct scmi_protocol_instance * __must_check
 scmi_get_protocol_instance(const struct scmi_handle *handle, u8 protocol_id)
 {
-	struct scmi_protocol_instance *pi;
 	struct scmi_info *info = handle_to_scmi_info(handle);
+	const struct scmi_protocol *proto;
 
-	mutex_lock(&info->protocols_mtx);
-	pi = idr_find(&info->protocols, protocol_id);
-
-	if (pi) {
-		refcount_inc(&pi->users);
-	} else {
-		const struct scmi_protocol *proto;
+	scoped_guard(mutex, &info->protocols_mtx) {
+		struct scmi_protocol_instance *pi;
 
-		/* Fails if protocol not registered on bus */
-		proto = scmi_protocol_get(protocol_id, &info->version);
-		if (proto)
-			pi = scmi_alloc_init_protocol_instance(info, proto);
-		else
-			pi = ERR_PTR(-EPROBE_DEFER);
+		pi = idr_find(&info->protocols, protocol_id);
+		if (pi) {
+			refcount_inc(&pi->users);
+			return pi;
+		}
 	}
-	mutex_unlock(&info->protocols_mtx);
 
-	return pi;
+	/* Fails if protocol not registered on bus */
+	proto = scmi_protocol_get(protocol_id, &info->version);
+	if (!proto)
+		return ERR_PTR(-EPROBE_DEFER);
+
+	return scmi_alloc_init_protocol_instance(info, proto);
 }
 
 /**
@@ -2277,10 +2277,11 @@ void scmi_protocol_release(const struct scmi_handle *handle, u8 protocol_id)
 	struct scmi_info *info = handle_to_scmi_info(handle);
 	struct scmi_protocol_instance *pi;
 
-	mutex_lock(&info->protocols_mtx);
-	pi = idr_find(&info->protocols, protocol_id);
-	if (WARN_ON(!pi))
-		goto out;
+	scoped_guard(mutex, &info->protocols_mtx) {
+		pi = idr_find(&info->protocols, protocol_id);
+		if (WARN_ON(!pi))
+			return;
+	}
 
 	if (refcount_dec_and_test(&pi->users)) {
 		void *gid = pi->gid;
@@ -2299,9 +2300,6 @@ void scmi_protocol_release(const struct scmi_handle *handle, u8 protocol_id)
 		dev_dbg(handle->dev, "De-Initialized protocol: 0x%X\n",
 			protocol_id);
 	}
-
-out:
-	mutex_unlock(&info->protocols_mtx);
 }
 
 void scmi_setup_protocol_implemented(const struct scmi_protocol_handle *ph,
-- 
2.52.0