coresight: tmc-etr: Decouple buffer sync and barrier packet insertion

If less space is available in the perf ring buffer than the ETR buffer,
barrier packets inserted in the trace stream by tmc_sync_etr_buf() are
skipped over when the head of the buffer is moved forward, resulting in
traces that can't be decoded.

This patch decouples the process of syncing ETR buffers and the addition
of barrier packets in order to perform the latter once the offset in the
trace buffer has been properly computed.
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Reviewed-by: Leo Yan <leo.yan@linaro.org>
Link: https://lore.kernel.org/r/20190829202842.580-17-mathieu.poirier@linaro.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

@@ -946,10 +946,6 @@ static void tmc_sync_etr_buf(struct tmc_drvdata *drvdata)
 	WARN_ON(!etr_buf->ops || !etr_buf->ops->sync);
 
 	etr_buf->ops->sync(etr_buf, rrp, rwp);
-
-	/* Insert barrier packets at the beginning, if there was an overflow */
-	if (etr_buf->full)
-		tmc_etr_buf_insert_barrier_packet(etr_buf, etr_buf->offset);
 }
 
 static void __tmc_etr_enable_hw(struct tmc_drvdata *drvdata)
@@ -1086,6 +1082,13 @@ static void tmc_etr_sync_sysfs_buf(struct tmc_drvdata *drvdata)
 		drvdata->sysfs_buf = NULL;
 	} else {
 		tmc_sync_etr_buf(drvdata);
+		/*
+		 * Insert barrier packets at the beginning, if there was
+		 * an overflow.
+		 */
+		if (etr_buf->full)
+			tmc_etr_buf_insert_barrier_packet(etr_buf,
+							  etr_buf->offset);
 	}
 }
 
@@ -1502,11 +1505,16 @@ tmc_update_etr_buffer(struct coresight_device *csdev,
 	CS_LOCK(drvdata->base);
 	spin_unlock_irqrestore(&drvdata->spinlock, flags);
 
+	lost = etr_buf->full;
 	size = etr_buf->len;
 	if (!etr_perf->snapshot && size > handle->size) {
 		size = handle->size;
 		lost = true;
 	}
+
+	/* Insert barrier packets at the beginning, if there was an overflow */
+	if (lost)
+		tmc_etr_buf_insert_barrier_packet(etr_buf, etr_buf->offset);
 	tmc_etr_sync_perf_buffer(etr_perf, size);
 
 	/*
@@ -1517,8 +1525,6 @@ tmc_update_etr_buffer(struct coresight_device *csdev,
 	 */
 	if (etr_perf->snapshot)
 		handle->head += size;
-
-	lost |= etr_buf->full;
 out:
 	/*
 	 * Don't set the TRUNCATED flag in snapshot mode because 1) the