coresight: Add helper for atomically taking the device

Now that mode is in struct coresight_device, this pattern can be wrapped
in a helper.
Signed-off-by: James Clark <james.clark@arm.com>
Link: https://lore.kernel.org/r/20240129154050.569566-11-james.clark@arm.comSigned-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>

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:

drivers/hwtracing/coresight/coresight-etm4x-core.c

@@ -840,13 +840,11 @@ 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:

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);
 

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);