2b1c6b21b5
As usual these patches were extracted and rebased from the raspberry pi repo: https://github.com/raspberrypi/linux/tree/rpi-4.4.y Also adds support for Raspberry Pi Compute Module 3 (untested). Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>
80 lines
2.9 KiB
Diff
80 lines
2.9 KiB
Diff
From 4b235ff95b0fcfa9731c1159402f4fef0e26f1d3 Mon Sep 17 00:00:00 2001
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From: wm4 <wm4@nowhere>
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Date: Wed, 13 Jan 2016 19:42:18 +0100
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Subject: [PATCH] bcm2835: restrict channels*rate to 8*960000
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This is required at least for SPDIF. If the bitrate goes above,
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videocore will either resample the audio or corrupt it due to
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underruns. Supposedly the hardware isn't designed to output
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higher rates, but it can still resample it down to supported
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rates.
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Some code is based on ac97_pcm.c.
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---
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sound/arm/bcm2835-pcm.c | 41 +++++++++++++++++++++++++++++++++++++++++
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1 file changed, 41 insertions(+)
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--- a/sound/arm/bcm2835-pcm.c
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+++ b/sound/arm/bcm2835-pcm.c
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@@ -19,6 +19,9 @@
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#include "bcm2835.h"
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+/* The hardware can not do much more num_channels*samplerate then this value */
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+#define MAX_COMBINED_RATE 768000
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+
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/* hardware definition */
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static struct snd_pcm_hardware snd_bcm2835_playback_hw = {
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.info = (SNDRV_PCM_INFO_INTERLEAVED | SNDRV_PCM_INFO_BLOCK_TRANSFER |
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@@ -107,6 +110,31 @@ static irqreturn_t bcm2835_playback_fifo
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return IRQ_HANDLED;
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}
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+
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+static int rate_hw_constraint_rate(struct snd_pcm_hw_params *params,
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+ struct snd_pcm_hw_rule *rule)
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+{
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+ struct snd_interval *channels = hw_param_interval(params, SNDRV_PCM_HW_PARAM_CHANNELS);
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+ struct snd_interval rates = {
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+ .min = 8000,
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+ .max = min(192000u, MAX_COMBINED_RATE / max(channels->min, 1u)),
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+ };
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+ struct snd_interval *rate = hw_param_interval(params, SNDRV_PCM_HW_PARAM_RATE);
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+ return snd_interval_refine(rate, &rates);
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+}
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+
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+static int rate_hw_constraint_channels(struct snd_pcm_hw_params *params,
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+ struct snd_pcm_hw_rule *rule)
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+{
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+ struct snd_interval *rate = hw_param_interval(params, SNDRV_PCM_HW_PARAM_RATE);
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+ struct snd_interval channels_interval = {
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+ .min = 1,
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+ .max = min(8u, MAX_COMBINED_RATE / max(rate->min, 1u)),
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+ };
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+ struct snd_interval *channels = hw_param_interval(params, SNDRV_PCM_HW_PARAM_CHANNELS);
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+ return snd_interval_refine(channels, &channels_interval);
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+}
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+
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/* open callback */
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static int snd_bcm2835_playback_open_generic(
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struct snd_pcm_substream *substream, int spdif)
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@@ -188,6 +216,19 @@ static int snd_bcm2835_playback_open_gen
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snd_pcm_hw_constraint_step(runtime, 0, SNDRV_PCM_HW_PARAM_PERIOD_BYTES,
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16);
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+ /* When playing PCM, pretend that we support the full range of channels
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+ * and sample rates. The GPU can't output it, but is able to resample
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+ * the data to a rate the hardware can handle it. This won't work with
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+ * compressed data; the resampler would just destroy it. */
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+ if (spdif) {
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+ err = snd_pcm_hw_rule_add(runtime, 0, SNDRV_PCM_HW_PARAM_RATE,
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+ rate_hw_constraint_rate, NULL,
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+ SNDRV_PCM_HW_PARAM_CHANNELS, -1);
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+ err = snd_pcm_hw_rule_add(runtime, 0, SNDRV_PCM_HW_PARAM_CHANNELS,
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+ rate_hw_constraint_channels, NULL,
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+ SNDRV_PCM_HW_PARAM_RATE, -1);
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+ }
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+
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chip->alsa_stream[idx] = alsa_stream;
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chip->opened |= (1 << idx);
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