[SRU][N][PATCH 10/13] coresight: Add helper for atomically taking the device

[Noah Wager]

From: James Clark <james.clark at arm.com>

BugLink: https://bugs.launchpad.net/bugs/2142336

Now that mode is in struct coresight_device, this pattern can be wrapped
in a helper.

Signed-off-by: James Clark <james.clark at arm.com>
Link: https://lore.kernel.org/r/20240129154050.569566-11-james.clark@arm.com
Signed-off-by: Suzuki K Poulose <suzuki.poulose at arm.com>
(cherry picked from commit d724f65218b994da234081df5dfe417c23802a65)
Signed-off-by: Noah Wager <noah.wager at canonical.com>
---
 drivers/hwtracing/coresight/coresight-etm3x-core.c |  8 +++-----
 drivers/hwtracing/coresight/coresight-etm4x-core.c |  8 +++-----
 drivers/hwtracing/coresight/coresight-stm.c        |  8 +++-----
 include/linux/coresight.h                          | 11 +++++++++++
 4 files changed, 20 insertions(+), 15 deletions(-)

diff --git a/drivers/hwtracing/coresight/coresight-etm3x-core.c b/drivers/hwtracing/coresight/coresight-etm3x-core.c
index a8be115636f0..ce2b3ed90fb9 100644
--- a/drivers/hwtracing/coresight/coresight-etm3x-core.c
+++ b/drivers/hwtracing/coresight/coresight-etm3x-core.c
@@ -556,14 +556,12 @@ static int etm_enable(struct coresight_device *csdev, struct perf_event *event,
 		      enum cs_mode mode)
 {
 	int ret;
-	u32 val;
 	struct etm_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
 
-	val = local_cmpxchg(&drvdata->csdev->mode, CS_MODE_DISABLED, mode);
-
-	/* Someone is already using the tracer */
-	if (val)
+	if (!coresight_take_mode(csdev, mode)) {
+		/* Someone is already using the tracer */
 		return -EBUSY;
+	}
 
 	switch (mode) {
 	case CS_MODE_SYSFS:
diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
index 898dc2cafeec..26213f8c25fc 100644
--- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
+++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
@@ -864,13 +864,11 @@ static int etm4_enable(struct coresight_device *csdev, struct perf_event *event,
 		       enum cs_mode mode)
 {
 	int ret;
-	u32 val;
 
-	val = local_cmpxchg(&csdev->mode, CS_MODE_DISABLED, mode);
-
-	/* Someone is already using the tracer */
-	if (val)
+	if (!coresight_take_mode(csdev, mode)) {
+		/* Someone is already using the tracer */
 		return -EBUSY;
+	}
 
 	switch (mode) {
 	case CS_MODE_SYSFS:
diff --git a/drivers/hwtracing/coresight/coresight-stm.c b/drivers/hwtracing/coresight/coresight-stm.c
index af9b21224246..80fed4c377f1 100644
--- a/drivers/hwtracing/coresight/coresight-stm.c
+++ b/drivers/hwtracing/coresight/coresight-stm.c
@@ -193,17 +193,15 @@ static void stm_enable_hw(struct stm_drvdata *drvdata)
 static int stm_enable(struct coresight_device *csdev, struct perf_event *event,
 		      enum cs_mode mode)
 {
-	u32 val;
 	struct stm_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
 
 	if (mode != CS_MODE_SYSFS)
 		return -EINVAL;
 
-	val = local_cmpxchg(&csdev->mode, CS_MODE_DISABLED, mode);
-
-	/* Someone is already using the tracer */
-	if (val)
+	if (!coresight_take_mode(csdev, mode)) {
+		/* Someone is already using the tracer */
 		return -EBUSY;
+	}
 
 	pm_runtime_get_sync(csdev->dev.parent);
 
diff --git a/include/linux/coresight.h b/include/linux/coresight.h
index c8f41d9c17a9..9f1a78246a88 100644
--- a/include/linux/coresight.h
+++ b/include/linux/coresight.h
@@ -580,6 +580,17 @@ static inline bool coresight_is_percpu_sink(struct coresight_device *csdev)
 	       (csdev->subtype.sink_subtype == CORESIGHT_DEV_SUBTYPE_SINK_PERCPU_SYSMEM);
 }
 
+/*
+ * Atomically try to take the device and set a new mode. Returns true on
+ * success, false if the device is already taken by someone else.
+ */
+static inline bool coresight_take_mode(struct coresight_device *csdev,
+				       enum cs_mode new_mode)
+{
+	return local_cmpxchg(&csdev->mode, CS_MODE_DISABLED, new_mode) ==
+	       CS_MODE_DISABLED;
+}
+
 extern struct coresight_device *
 coresight_register(struct coresight_desc *desc);
 extern void coresight_unregister(struct coresight_device *csdev);
-- 
2.43.0