target/linux/brcm2708/patches-4.4/0129-bcm2835-restrict-channels-rate-to-8-960000.patch

   1 From 7e634c8f8fe70286e0b8b404494d3143aa7bc3fc Mon Sep 17 00:00:00 2001
   2 From: wm4 <wm4@nowhere>
   3 Date: Wed, 13 Jan 2016 19:42:18 +0100
   4 Subject: [PATCH 129/170] bcm2835: restrict channels*rate to 8*960000
   5
   6 This is required at least for SPDIF. If the bitrate goes above,
   7 videocore will either resample the audio or corrupt it due to
   8 underruns. Supposedly the hardware isn't designed to output
   9 higher rates, but it can still resample it down to supported
  10 rates.
  11
  12 Some code is based on ac97_pcm.c.
  13 ---
  14  sound/arm/bcm2835-pcm.c | 41 +++++++++++++++++++++++++++++++++++++++++
  15  1 file changed, 41 insertions(+)
  16
  17 --- a/sound/arm/bcm2835-pcm.c
  18 +++ b/sound/arm/bcm2835-pcm.c
  19 @@ -19,6 +19,9 @@
  20
  21  #include "bcm2835.h"
  22
  23 +/* The hardware can not do much more num_channels*samplerate then this value */
  24 +#define MAX_COMBINED_RATE 768000
  25 +
  26  /* hardware definition */
  27  static struct snd_pcm_hardware snd_bcm2835_playback_hw = {
  28         .info = (SNDRV_PCM_INFO_INTERLEAVED | SNDRV_PCM_INFO_BLOCK_TRANSFER |
  29 @@ -107,6 +110,31 @@ static irqreturn_t bcm2835_playback_fifo
  30         return IRQ_HANDLED;
  31  }
  32
  33 +
  34 +static int rate_hw_constraint_rate(struct snd_pcm_hw_params *params,
  35 +                                  struct snd_pcm_hw_rule *rule)
  36 +{
  37 +       struct snd_interval *channels = hw_param_interval(params, SNDRV_PCM_HW_PARAM_CHANNELS);
  38 +       struct snd_interval rates = {
  39 +               .min = 8000,
  40 +               .max = min(192000u, MAX_COMBINED_RATE / max(channels->min, 1u)),
  41 +       };
  42 +       struct snd_interval *rate = hw_param_interval(params, SNDRV_PCM_HW_PARAM_RATE);
  43 +       return snd_interval_refine(rate, &rates);
  44 +}
  45 +
  46 +static int rate_hw_constraint_channels(struct snd_pcm_hw_params *params,
  47 +                                      struct snd_pcm_hw_rule *rule)
  48 +{
  49 +       struct snd_interval *rate = hw_param_interval(params, SNDRV_PCM_HW_PARAM_RATE);
  50 +       struct snd_interval channels_interval = {
  51 +               .min = 1,
  52 +               .max = min(8u, MAX_COMBINED_RATE / max(rate->min, 1u)),
  53 +       };
  54 +       struct snd_interval *channels = hw_param_interval(params, SNDRV_PCM_HW_PARAM_CHANNELS);
  55 +       return snd_interval_refine(channels, &channels_interval);
  56 +}
  57 +
  58  /* open callback */
  59  static int snd_bcm2835_playback_open_generic(
  60                 struct snd_pcm_substream *substream, int spdif)
  61 @@ -188,6 +216,19 @@ static int snd_bcm2835_playback_open_gen
  62         snd_pcm_hw_constraint_step(runtime, 0, SNDRV_PCM_HW_PARAM_PERIOD_BYTES,
  63                                    16);
  64
  65 +       /* When playing PCM, pretend that we support the full range of channels
  66 +        * and sample rates. The GPU can't output it, but is able to resample
  67 +        * the data to a rate the hardware can handle it. This won't work with
  68 +        * compressed data; the resampler would just destroy it. */
  69 +       if (spdif) {
  70 +               err = snd_pcm_hw_rule_add(runtime, 0, SNDRV_PCM_HW_PARAM_RATE,
  71 +                                         rate_hw_constraint_rate, NULL,
  72 +                                         SNDRV_PCM_HW_PARAM_CHANNELS, -1);
  73 +               err = snd_pcm_hw_rule_add(runtime, 0, SNDRV_PCM_HW_PARAM_CHANNELS,
  74 +                                         rate_hw_constraint_channels, NULL,
  75 +                                         SNDRV_PCM_HW_PARAM_RATE, -1);
  76 +       }
  77 +
  78         chip->alsa_stream[idx] = alsa_stream;
  79
  80         chip->opened |= (1 << idx);