target/linux/brcm2708/patches-4.4/0404-dmaengine-bcm2835-Fix-cyclic-DMA-period-splitting.patch

   1 From 9c9db58d0b33e3fd7e67a3fc9910184e6f4d2f95 Mon Sep 17 00:00:00 2001
   2 From: Matthias Reichl <hias@horus.com>
   3 Date: Tue, 7 Jun 2016 19:37:10 +0200
   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 ---
  21  drivers/dma/bcm2835-dma.c | 5 ++++-
  22  1 file changed, 4 insertions(+), 1 deletion(-)
  23
  24 --- a/drivers/dma/bcm2835-dma.c
  25 +++ b/drivers/dma/bcm2835-dma.c
  26 @@ -252,8 +252,11 @@ static void bcm2835_dma_create_cb_set_le
  27          */
  28
  29         /* have we filled in period_length yet? */
  30 -       if (*total_len + control_block->length < period_len)
  31 +       if (*total_len + control_block->length < period_len) {
  32 +               /* update number of bytes in this period so far */
  33 +               *total_len += control_block->length;
  34                 return;
  35 +       }
  36
  37         /* calculate the length that remains to reach period_length */
  38         control_block->length = period_len - *total_len;