coresight: tmc-etr: Introduce the notion of reference counting to ETR devices

This patch adds reference counting to struct etr_buf so that, in CPU-wide
trace scenarios, shared buffers can be disposed of when no longer used.
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Tested-by: Leo Yan <leo.yan@linaro.org>
Tested-by: Robert Walker <robert.walker@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/hwtracing/coresight/coresight-tmc-etr.c

@@ -8,6 +8,7 @@
 #include <linux/coresight.h>
 #include <linux/dma-mapping.h>
 #include <linux/iommu.h>
+#include <linux/refcount.h>
 #include <linux/slab.h>
 #include <linux/types.h>
 #include <linux/vmalloc.h>
@@ -1222,7 +1223,11 @@ get_perf_etr_buf_per_thread(struct tmc_drvdata *drvdata,
 	 * with memory allocation.
 	 */
 	etr_buf = alloc_etr_buf(drvdata, event, nr_pages, pages, snapshot);
+	if (IS_ERR(etr_buf))
+		goto out;
 
+	refcount_set(&etr_buf->refcount, 1);
+out:
 	return etr_buf;
 }
 

drivers/hwtracing/coresight/coresight-tmc.h

@@ -9,6 +9,7 @@
 
 #include <linux/dma-mapping.h>
 #include <linux/miscdevice.h>
+#include <linux/refcount.h>
 
 #define TMC_RSZ			0x004
 #define TMC_STS			0x00c
@@ -133,6 +134,7 @@ struct etr_buf_operations;
 
 /**
  * struct etr_buf - Details of the buffer used by ETR
+ * refcount	; Number of sources currently using this etr_buf.
  * @mode	: Mode of the ETR buffer, contiguous, Scatter Gather etc.
  * @full	: Trace data overflow
  * @size	: Size of the buffer.
@@ -143,6 +145,7 @@ struct etr_buf_operations;
  * @private	: Backend specific information for the buf
  */
 struct etr_buf {
+	refcount_t			refcount;
 	enum etr_mode			mode;
 	bool				full;
 	ssize_t				size;