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

   1 From fc5bc111e65b27883284591aec9db5a290665ac9 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] bcm2835-dma: Limit cyclic transfers on lite channels to 32k
   5
   6 Transfers larger than 32k cause repeated clicking with I2S soundcards.
   7 The exact reason is yet unknown, so limit to 32k as bcm2708-dmaengine
   8 did as an intermediate fix.
   9 ---
  10  drivers/dma/bcm2835-dma.c | 8 +++++++-
  11  1 file changed, 7 insertions(+), 1 deletion(-)
  12
  13 --- a/drivers/dma/bcm2835-dma.c
  14 +++ b/drivers/dma/bcm2835-dma.c
  15 @@ -144,6 +144,12 @@ struct bcm2835_desc {
  16   */
  17  #define MAX_LITE_TRANSFER      (SZ_64K - 4)
  18
  19 +/*
  20 + * Transfers larger than 32k cause issues with the bcm2708-i2s driver,
  21 + * so limit transfer size to 32k as bcm2708-dmaengine did.
  22 + */
  23 +#define MAX_CYCLIC_LITE_TRANSFER       SZ_32K
  24 +
  25  static inline struct bcm2835_dmadev *to_bcm2835_dma_dev(struct dma_device *d)
  26  {
  27         return container_of(d, struct bcm2835_dmadev, ddev);
  28 @@ -412,7 +418,7 @@ static struct dma_async_tx_descriptor *b
  29         d->c = c;
  30         d->dir = direction;
  31         if (c->ch >= 8) /* LITE channel */
  32 -               max_size = MAX_LITE_TRANSFER;
  33 +               max_size = MAX_CYCLIC_LITE_TRANSFER;
  34         else
  35                 max_size = MAX_NORMAL_TRANSFER;
  36         period_len = min(period_len, max_size);