[PATCH V2 3/6] coresight: tmc-etf: Properly set AUX buffer head in snapshot mode

Mathieu Poirier
2019-05-14T19:41:03Z

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-etf.c | 14 +++++++++-----
1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/drivers/hwtracing/coresight/coresight-tmc-etf.c b/drivers/hwtracing/coresight/coresight-tmc-etf.c
index 2527b5d3b65e..d026bd04a6af 100644
--- a/drivers/hwtracing/coresight/coresight-tmc-etf.c
+++ b/drivers/hwtracing/coresight/coresight-tmc-etf.c
@@ -542,11 +542,15 @@ static unsigned long tmc_update_etf_buffer(struct coresight_device *csdev,
}
}

- /* In snapshot mode we have to update the head */
- if (buf->snapshot) {
- handle->head = (cur * PAGE_SIZE) + offset;
- to_read = buf->nr_pages << PAGE_SHIFT;
- }
+ /*
+ * 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 (buf->snapshot)
+ handle->head += to_read;
+
CS_LOCK(drvdata->base);
out:
spin_unlock_irqrestore(&drvdata->spinlock, flags);
--
2.17.1