[PATCH v11 25/27] coresight: sysfs: Increment refcount only for system tracers

Leo Yan
2026-05-01T16:49:32Z

Except for system tracers (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.

Refactor to maintain the refcount only for system 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>
---
drivers/hwtracing/coresight/coresight-sysfs.c | 41 ++++++++++++++++++---------
1 file changed, 27 insertions(+), 14 deletions(-)

diff --git a/drivers/hwtracing/coresight/coresight-sysfs.c b/drivers/hwtracing/coresight/coresight-sysfs.c
index 0aebafcb8d0e8e699652244af5202e7c4dc4e9b1..42cf07b8d15a420e963650000dc32bbb38f0aa62 100644
--- a/drivers/hwtracing/coresight/coresight-sysfs.c
+++ b/drivers/hwtracing/coresight/coresight-sysfs.c
@@ -39,6 +39,28 @@ 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 (csdev->subtype.source_subtype ==
+ CORESIGHT_DEV_SUBTYPE_SOURCE_SOFTWARE)
+ csdev->refcnt++;
+}
+
+static void coresight_source_put_refcnt(struct coresight_device *csdev)
+{
+ if (csdev->subtype.source_subtype ==
+ CORESIGHT_DEV_SUBTYPE_SOURCE_SOFTWARE)
+ csdev->refcnt--;
+}
+
static int coresight_enable_source_sysfs(struct coresight_device *csdev,
enum cs_mode mode,
struct coresight_path *path)
@@ -57,14 +79,14 @@ 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 +101,7 @@ 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 +178,6 @@ 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 +192,7 @@ 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;
}

--
2.34.1