target/linux/brcm2708/patches-4.4/0299-bcm2835-i2s-Reduce-the-TX-DREQ-threshold.patch

   1 From c2dd47a309d6eee486191ef7805ba3f544ff3dae Mon Sep 17 00:00:00 2001
   2 From: Phil Elwell <phil@raspberrypi.org>
   3 Date: Thu, 21 Apr 2016 15:44:14 +0100
   4 Subject: [PATCH 299/423] bcm2835-i2s: Reduce the TX DREQ threshold
   5
   6 TX FIFO overrun is thought to be the cause of channel swapping, so
   7 reducing the DREQ threshold seems reasonable and appears to be
   8 effective.
   9
  10 See: https://github.com/raspberrypi/linux/issues/1417
  11
  12 Signed-off-by: Phil Elwell <phil@raspberrypi.org>
  13 ---
  14  sound/soc/bcm/bcm2835-i2s.c | 21 ++++++++++++++-------
  15  1 file changed, 14 insertions(+), 7 deletions(-)
  16
  17 --- a/sound/soc/bcm/bcm2835-i2s.c
  18 +++ b/sound/soc/bcm/bcm2835-i2s.c
  19 @@ -555,15 +555,22 @@ static int bcm2835_i2s_hw_params(struct
  20
  21         /* Setup the DMA parameters */
  22         regmap_update_bits(dev->i2s_regmap, BCM2835_I2S_CS_A_REG,
  23 -                       BCM2835_I2S_RXTHR(1)
  24 -                       | BCM2835_I2S_TXTHR(1)
  25 -                       | BCM2835_I2S_DMAEN, 0xffffffff);
  26 +                          BCM2835_I2S_RXTHR(3)
  27 +                          | BCM2835_I2S_TXTHR(3)
  28 +                          | BCM2835_I2S_DMAEN,
  29 +                          BCM2835_I2S_RXTHR(1)
  30 +                          | BCM2835_I2S_TXTHR(1)
  31 +                          | BCM2835_I2S_DMAEN);
  32
  33         regmap_update_bits(dev->i2s_regmap, BCM2835_I2S_DREQ_A_REG,
  34 -                         BCM2835_I2S_TX_PANIC(0x10)
  35 -                       | BCM2835_I2S_RX_PANIC(0x30)
  36 -                       | BCM2835_I2S_TX(0x30)
  37 -                       | BCM2835_I2S_RX(0x20), 0xffffffff);
  38 +                          BCM2835_I2S_TX_PANIC(0x7f)
  39 +                          | BCM2835_I2S_RX_PANIC(0x7f)
  40 +                          | BCM2835_I2S_TX(0x7f)
  41 +                          | BCM2835_I2S_RX(0x7f),
  42 +                          BCM2835_I2S_TX_PANIC(0x10)
  43 +                          | BCM2835_I2S_RX_PANIC(0x30)
  44 +                          | BCM2835_I2S_TX(0x20)
  45 +                          | BCM2835_I2S_RX(0x20));
  46
  47         /* Clear FIFOs */
  48         bcm2835_i2s_clear_fifos(dev, true, true);