releases/4.14.111/dmaengine-tegra-avoid-overflow-of-byte-tracking.patch

   1 From fdec0ac5e8f3bf2a5ccb0cca2e4326eacb70ee02 Mon Sep 17 00:00:00 2001
   2 From: Ben Dooks <ben.dooks@codethink.co.uk>
   3 Date: Wed, 21 Nov 2018 16:13:19 +0000
   4 Subject: dmaengine: tegra: avoid overflow of byte tracking
   5
   6 [ Upstream commit e486df39305864604b7e25f2a95d51039517ac57 ]
   7
   8 The dma_desc->bytes_transferred counter tracks the number of bytes
   9 moved by the DMA channel. This is then used to calculate the information
  10 passed back in the in the tegra_dma_tx_status callback, which is usually
  11 fine.
  12
  13 When the DMA channel is configured as continous, then the bytes_transferred
  14 counter will increase over time and eventually overflow to become negative
  15 so the residue count will become invalid and the ALSA sound-dma code will
  16 report invalid hardware pointer values to the application. This results in
  17 some users becoming confused about the playout position and putting audio
  18 data in the wrong place.
  19
  20 To fix this issue, always ensure the bytes_transferred field is modulo the
  21 size of the request. We only do this for the case of the cyclic transfer
  22 done ISR as anyone attempting to move 2GiB of DMA data in one transfer
  23 is unlikely.
  24
  25 Note, we don't fix the issue that we should /never/ transfer a negative
  26 number of bytes so we could make those fields unsigned.
  27
  28 Reviewed-by: Dmitry Osipenko <digetx@gmail.com>
  29 Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
  30 Acked-by: Jon Hunter <jonathanh@nvidia.com>
  31 Signed-off-by: Vinod Koul <vkoul@kernel.org>
  32 Signed-off-by: Sasha Levin <sashal@kernel.org>
  33 ---
  34  drivers/dma/tegra20-apb-dma.c | 5 ++++-
  35  1 file changed, 4 insertions(+), 1 deletion(-)
  36
  37 diff --git a/drivers/dma/tegra20-apb-dma.c b/drivers/dma/tegra20-apb-dma.c
  38 index b9d75a54c896..7db2766b5fe9 100644
  39 --- a/drivers/dma/tegra20-apb-dma.c
  40 +++ b/drivers/dma/tegra20-apb-dma.c
  41 @@ -635,7 +635,10 @@ static void handle_cont_sngl_cycle_dma_done(struct tegra_dma_channel *tdc,
  42
  43         sgreq = list_first_entry(&tdc->pending_sg_req, typeof(*sgreq), node);
  44         dma_desc = sgreq->dma_desc;
  45 -       dma_desc->bytes_transferred += sgreq->req_len;
  46 +       /* if we dma for long enough the transfer count will wrap */
  47 +       dma_desc->bytes_transferred =
  48 +               (dma_desc->bytes_transferred + sgreq->req_len) %
  49 +               dma_desc->bytes_requested;
  50
  51         /* Callback need to be call */
  52         if (!dma_desc->cb_count)
  53 --
  54 2.19.1
  55