1 files changed, 24 insertions, 2 deletions

diff --git a/drivers/dma/edma.c b/drivers/dma/edma.c
index 5d9f57f27ffb..18c833fa1646 100644
--- a/drivers/dma/edma.c
+++ b/drivers/dma/edma.c
@@ -70,12 +70,34 @@ struct edma_desc {
         int                             cyclic;
         int                             absync;
         int                             pset_nr;
+        struct edma_chan                *echan;
         int                             processed;
+
+        /*
+         * The following 4 elements are used for residue accounting.
+         *
+         * - processed_stat: the number of SG elements we have traversed
+         * so far to cover accounting. This is updated directly to processed
+         * during edma_callback and is always <= processed, because processed
+         * refers to the number of pending transfer (programmed to EDMA
+         * controller), where as processed_stat tracks number of transfers
+         * accounted for so far.
+         *
+         * - residue: The amount of bytes we have left to transfer for this desc
+         *
+         * - residue_stat: The residue in bytes of data we have covered
+         * so far for accounting. This is updated directly to residue
+         * during callbacks to keep it current.
+         *
+         * - sg_len: Tracks the length of the current intermediate transfer,
+         * this is required to update the residue during intermediate transfer
+         * completion callback.
+         */
         int                             processed_stat;
-        u32                             residue;
         u32                             sg_len;
+        u32                             residue;
         u32                             residue_stat;
-        struct edma_chan                *echan;
+
         struct edma_pset                pset[0];
 };