coresight: trbe: Add a helper to pad a given buffer area

Refactor the helper to pad a given AUX buffer area to allow
"filling" ignore packets, without moving any handle pointers.
This will be useful in working around errata, where we may
have to fill the buffer after a session.

Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Cc: Mike Leach <mike.leach@linaro.org>
Cc: Leo Yan <leo.yan@linaro.org>
Reviewed-by: NAnshuman Khandual <anshuman.khandual@arm.com>
Signed-off-by: NSuzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/20211019163153.3692640-7-suzuki.poulose@arm.comSigned-off-by: NMathieu Poirier <mathieu.poirier@linaro.org>

drivers/hwtracing/coresight/coresight-trbe.c

@@ -199,12 +199,18 @@ static void trbe_stop_and_truncate_event(struct perf_output_handle *handle)
  * consumed from the user space. The enabled TRBE buffer area is a moving subset of
  * the allocated perf auxiliary buffer.
  */
+
+static void __trbe_pad_buf(struct trbe_buf *buf, u64 offset, int len)
+{
+	memset((void *)buf->trbe_base + offset, ETE_IGNORE_PACKET, len);
+}
+
 static void trbe_pad_buf(struct perf_output_handle *handle, int len)
 {
 	struct trbe_buf *buf = etm_perf_sink_config(handle);
 	u64 head = PERF_IDX2OFF(handle->head, buf);
 
-	memset((void *)buf->trbe_base + head, ETE_IGNORE_PACKET, len);
+	__trbe_pad_buf(buf, head, len);
 	if (!buf->snapshot)
 		perf_aux_output_skip(handle, len);
 }