target/linux/brcm2708/patches-4.9/950-0187-dmaengine-bcm2835-Fix-cyclic-DMA-period-splitting.patch

   1 From 9fd7a158ec098ab05b8d3ec2c2973b3dc7e498f3 Mon Sep 17 00:00:00 2001
   2 From: Matthias Reichl <hias@horus.com>
   3 Date: Mon, 20 Feb 2017 20:01:16 +0100
   4 Subject: [PATCH] dmaengine: bcm2835: Fix cyclic DMA period splitting
   5
   6 The code responsible for splitting periods into chunks that
   7 can be handled by the DMA controller missed to update total_len,
   8 the number of bytes processed in the current period, when there
   9 are more chunks to follow.
  10
  11 Therefore total_len was stuck at 0 and the code didn't work at all.
  12 This resulted in a wrong control block layout and audio issues because
  13 the cyclic DMA callback wasn't executing on period boundaries.
  14
  15 Fix this by adding the missing total_len update.
  16
  17 Signed-off-by: Matthias Reichl <hias@horus.com>
  18 Signed-off-by: Martin Sperl <kernel@martin.sperl.org>
  19 Tested-by: Clive Messer <clive.messer@digitaldreamtime.co.uk>
  20 Reviewed-by: Eric Anholt <eric@anholt.net>
  21 ---
  22  drivers/dma/bcm2835-dma.c | 5 ++++-
  23  1 file changed, 4 insertions(+), 1 deletion(-)
  24
  25 --- a/drivers/dma/bcm2835-dma.c
  26 +++ b/drivers/dma/bcm2835-dma.c
  27 @@ -253,8 +253,11 @@ static void bcm2835_dma_create_cb_set_le
  28          */
  29
  30         /* have we filled in period_length yet? */
  31 -       if (*total_len + control_block->length < period_len)
  32 +       if (*total_len + control_block->length < period_len) {
  33 +               /* update number of bytes in this period so far */
  34 +               *total_len += control_block->length;
  35                 return;
  36 +       }
  37
  38         /* calculate the length that remains to reach period_length */
  39         control_block->length = period_len - *total_len;