Hi Dirk-san, > From: Dirk Behme, Sent: Friday, April 12, 2019 2:29 PM > > From: Achim Dahlhoff <Achim.Dahlhoff@xxxxxxxxxxxx> > > The tx_status poll in the rcar_dmac driver reads the status register > which indicates which chunk is busy (DMACHCRB). Afterwards the point > inside the chunk is read from DMATCRB. It is possible that the chunk > has changed between the two reads. The result is a non-monotonous > increase of the residue. Fix this by introducing a 'safe read' logic. > > Fixes: 73a47bd0da66 ("dmaengine: rcar-dmac: use TCRB instead of TCR for residue") I guess this driver has this issue potencially from previous of the commit (maybe commit ccadee9b1e9 ("dmaengine: rcar-dmac: Implement support for hardware descriptor lists"?). But, this patch seems good to fix the issue. So, Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@xxxxxxxxxxx> Best regards, Yoshihiro Shimoda