[PATCH V2 2/6] coresight: tmc-etr: Properly set AUX buffer head in snapshot mode

[Mathieu Poirier <mathieu.poirier@linaro.org>]

Unify amongst sink drivers how the AUX ring buffer head is communicated
to user space.  That way the same algorithm in cs_etm_find_snapshot()
can be used to determine where the latest data is and how much of it
to access.

Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
---
 drivers/hwtracing/coresight/coresight-tmc-etr.c | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/drivers/hwtracing/coresight/coresight-tmc-etr.c b/drivers/hwtracing/coresight/coresight-tmc-etr.c
index df6e4b0b84e9..cc8401c76c39 100644
--- a/drivers/hwtracing/coresight/coresight-tmc-etr.c
+++ b/drivers/hwtracing/coresight/coresight-tmc-etr.c
@@ -1501,14 +1501,13 @@ tmc_update_etr_buffer(struct coresight_device *csdev,
 	tmc_etr_sync_perf_buffer(etr_perf);
 
 	/*
-	 * Update handle->head in snapshot mode. Also update the size to the
-	 * hardware buffer size if there was an overflow.
+	 * In snapshot mode we simply increment the head by the number of byte
+	 * that were written.  User space function  cs_etm_find_snapshot() will
+	 * figure out how many bytes to get from the AUX buffer based on the
+	 * position of the head.
 	 */
-	if (etr_perf->snapshot) {
+	if (etr_perf->snapshot)
 		handle->head += size;
-		if (etr_buf->full)
-			size = etr_buf->size;
-	}
 
 	lost |= etr_buf->full;
 out:
-- 
2.17.1


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