target/linux/brcm2708/patches-4.4/0024-bcm2835-dma-Limit-cyclic-transfers-on-lite-channels-.patch

   1 From 8eb5210cea099d814f9e583358343d8680c5d05d Mon Sep 17 00:00:00 2001
   2 From: Matthias Reichl <hias@horus.com>
   3 Date: Sun, 11 Oct 2015 12:28:30 +0200
   4 Subject: [PATCH 024/423] bcm2835-dma: Limit cyclic transfers on lite channels
   5  to 32k
   6
   7 Transfers larger than 32k cause repeated clicking with I2S soundcards.
   8 The exact reason is yet unknown, so limit to 32k as bcm2708-dmaengine
   9 did as an intermediate fix.
  10 ---
  11  drivers/dma/bcm2835-dma.c | 8 +++++++-
  12  1 file changed, 7 insertions(+), 1 deletion(-)
  13
  14 --- a/drivers/dma/bcm2835-dma.c
  15 +++ b/drivers/dma/bcm2835-dma.c
  16 @@ -144,6 +144,12 @@ struct bcm2835_desc {
  17   */
  18  #define MAX_LITE_TRANSFER      (SZ_64K - 4)
  19
  20 +/*
  21 + * Transfers larger than 32k cause issues with the bcm2708-i2s driver,
  22 + * so limit transfer size to 32k as bcm2708-dmaengine did.
  23 + */
  24 +#define MAX_CYCLIC_LITE_TRANSFER       SZ_32K
  25 +
  26  static inline struct bcm2835_dmadev *to_bcm2835_dma_dev(struct dma_device *d)
  27  {
  28         return container_of(d, struct bcm2835_dmadev, ddev);
  29 @@ -412,7 +418,7 @@ static struct dma_async_tx_descriptor *b
  30         d->c = c;
  31         d->dir = direction;
  32         if (c->ch >= 8) /* LITE channel */
  33 -               max_size = MAX_LITE_TRANSFER;
  34 +               max_size = MAX_CYCLIC_LITE_TRANSFER;
  35         else
  36                 max_size = MAX_NORMAL_TRANSFER;
  37         period_len = min(period_len, max_size);