coresight: tmc-etr: Properly set AUX buffer head in snapshot mode

Unify amongst sink drivers how the AUX ring buffer head is communicated
to user space.  That way the same algorithm in user space 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>
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Tested-by: Leo Yan <leo.yan@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/hwtracing/coresight/coresight-tmc-etr.c b/drivers/hwtracing/coresight/coresight-tmc-etr.c
index df6e4b0b84e9319eb32a7f91830e9add166ce46a..cc8401c76c399e52c79cf9edf6318eb376e45dfe 100644 (file)
--- 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: