From: Leo Yan <leo.yan@arm.com>
Date: Fri, 15 May 2026 20:08:33 +0000 (+0100)
Subject: coresight: sysfs: Increment refcount only for software source
X-Git-Url: http://git.ipfire.org/gitweb/index.cgi?a=commitdiff_plain;h=bf64b06ede93a8b56bf4dce0809e4edd111ccf36;p=thirdparty%2Flinux.git

coresight: sysfs: Increment refcount only for software source

Except for software sources (e.g. STM), other sources treat multiple
enables as equivalent to a single enable. The device mode already
tracks the binary state, so it is redundant to operate refcount.

Introduce a helper coresight_is_software_source() for check software
source. Refactor to maintain the refcount only for software sources.
This simplifies future CPU PM handling without refcount logic.

Tested-by: James Clark <james.clark@linaro.org>
Reviewed-by: Yeoreum Yun <yeoreum.yun@arm.com>
Reviewed-by: James Clark <james.clark@linaro.org>
Tested-by: Jie Gan <jie.gan@oss.qualcomm.com>
Signed-off-by: Leo Yan <leo.yan@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/20260515-arm_coresight_path_power_management_improvement-v14-26-f88c4a3ecfe9@arm.com
---

diff --git a/drivers/hwtracing/coresight/coresight-sysfs.c b/drivers/hwtracing/coresight/coresight-sysfs.c
index 21196ee1d2bd..80b6b634a70d 100644
--- a/drivers/hwtracing/coresight/coresight-sysfs.c
+++ b/drivers/hwtracing/coresight/coresight-sysfs.c
@@ -39,6 +39,26 @@ ssize_t coresight_simple_show32(struct device *_dev,
 }
 EXPORT_SYMBOL_GPL(coresight_simple_show32);
 
+static void coresight_source_get_refcnt(struct coresight_device *csdev)
+{
+	/*
+	 * There could be multiple applications driving the software
+	 * source. So keep the refcount for each such user when the
+	 * source is already enabled.
+	 *
+	 * No need to increment the reference counter for other source
+	 * types, as multiple enables are the same as a single enable.
+	 */
+	if (coresight_is_software_source(csdev))
+		csdev->refcnt++;
+}
+
+static void coresight_source_put_refcnt(struct coresight_device *csdev)
+{
+	if (coresight_is_software_source(csdev))
+		csdev->refcnt--;
+}
+
 static int coresight_enable_source_sysfs(struct coresight_device *csdev,
 					 enum cs_mode mode,
 					 struct coresight_path *path)
@@ -57,14 +77,14 @@ static int coresight_enable_source_sysfs(struct coresight_device *csdev,
 			return ret;
 	}
 
-	csdev->refcnt++;
+	coresight_source_get_refcnt(csdev);
 
 	return 0;
 }
 
 /**
- *  coresight_disable_source_sysfs - Drop the reference count by 1 and disable
- *  the device if there are no users left.
+ *  coresight_disable_source_sysfs - Drop the reference count by 1 for software
+ *  sources. Disable the device if there are no users left.
  *
  *  @csdev: The coresight device to disable
  *  @data: Opaque data to pass on to the disable function of the source device.
@@ -79,7 +99,7 @@ static bool coresight_disable_source_sysfs(struct coresight_device *csdev,
 	if (coresight_get_mode(csdev) != CS_MODE_SYSFS)
 		return false;
 
-	csdev->refcnt--;
+	coresight_source_put_refcnt(csdev);
 	if (csdev->refcnt == 0) {
 		coresight_disable_source(csdev, data);
 		return true;
@@ -156,9 +176,6 @@ int coresight_enable_sysfs(struct coresight_device *csdev)
 	int ret = 0;
 	struct coresight_device *sink;
 	struct coresight_path *path;
-	enum coresight_dev_subtype_source subtype;
-
-	subtype = csdev->subtype.source_subtype;
 
 	mutex_lock(&coresight_mutex);
 
@@ -173,13 +190,7 @@ int coresight_enable_sysfs(struct coresight_device *csdev)
 	 * doesn't hold coresight_mutex.
 	 */
 	if (coresight_get_mode(csdev) == CS_MODE_SYSFS) {
-		/*
-		 * There could be multiple applications driving the software
-		 * source. So keep the refcount for each such user when the
-		 * source is already enabled.
-		 */
-		if (subtype == CORESIGHT_DEV_SUBTYPE_SOURCE_SOFTWARE)
-			csdev->refcnt++;
+		coresight_source_get_refcnt(csdev);
 		goto out;
 	}
 
diff --git a/include/linux/coresight.h b/include/linux/coresight.h
index 58d474b26980..76ef4c096512 100644
--- a/include/linux/coresight.h
+++ b/include/linux/coresight.h
@@ -611,6 +611,12 @@ static inline bool coresight_is_percpu_source(struct coresight_device *csdev)
 	       (csdev->subtype.source_subtype == CORESIGHT_DEV_SUBTYPE_SOURCE_PROC);
 }
 
+static inline bool coresight_is_software_source(struct coresight_device *csdev)
+{
+	return csdev && coresight_is_device_source(csdev) &&
+	       (csdev->subtype.source_subtype == CORESIGHT_DEV_SUBTYPE_SOURCE_SOFTWARE);
+}
+
 static inline bool coresight_is_percpu_sink(struct coresight_device *csdev)
 {
 	return csdev && (csdev->type == CORESIGHT_DEV_TYPE_SINK) &&