[ALSA] cmipci: fix distortion on rear channels
Clemens Ladisch [Mon, 17 Sep 2007 07:41:36 +0000 (09:41 +0200)]
When playing multichannel data, the rear channels can get distorted if
the last sample of the last played stereo stream was not zero.  To avoid
this, add a hack to play a few silence samples after the stream is
stopped.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>

sound/pci/cmipci.c

index 085a367..6832649 100644 (file)
@@ -434,6 +434,7 @@ struct cmipci_pcm {
        u8 running;             /* dac/adc running? */
        u8 fmt;                 /* format bits */
        u8 is_dac;
+       u8 needs_silencing;
        unsigned int dma_size;  /* in frames */
        unsigned int shift;
        unsigned int ch;        /* channel (0/1) */
@@ -903,6 +904,7 @@ static int snd_cmipci_pcm_trigger(struct cmipci *cm, struct cmipci_pcm *rec,
                cm->ctrl &= ~chen;
                snd_cmipci_write(cm, CM_REG_FUNCTRL0, cm->ctrl | reset);
                snd_cmipci_write(cm, CM_REG_FUNCTRL0, cm->ctrl & ~reset);
+               rec->needs_silencing = rec->is_dac;
                break;
        case SNDRV_PCM_TRIGGER_PAUSE_PUSH:
        case SNDRV_PCM_TRIGGER_SUSPEND:
@@ -1304,11 +1306,75 @@ static int snd_cmipci_playback_spdif_prepare(struct snd_pcm_substream *substream
        return snd_cmipci_pcm_prepare(cm, &cm->channel[CM_CH_PLAY], substream);
 }
 
+/*
+ * Apparently, the samples last played on channel A stay in some buffer, even
+ * after the channel is reset, and get added to the data for the rear DACs when
+ * playing a multichannel stream on channel B.  This is likely to generate
+ * wraparounds and thus distortions.
+ * To avoid this, we play at least one zero sample after the actual stream has
+ * stopped.
+ */
+static void snd_cmipci_silence_hack(struct cmipci *cm, struct cmipci_pcm *rec)
+{
+       struct snd_pcm_runtime *runtime = rec->substream->runtime;
+       unsigned int reg, val;
+
+       if (rec->needs_silencing && runtime && runtime->dma_area) {
+               /* set up a small silence buffer */
+               memset(runtime->dma_area, 0, PAGE_SIZE);
+               reg = rec->ch ? CM_REG_CH1_FRAME2 : CM_REG_CH0_FRAME2;
+               val = ((PAGE_SIZE / 4) - 1) | (((PAGE_SIZE / 4) / 2 - 1) << 16);
+               snd_cmipci_write(cm, reg, val);
+       
+               /* configure for 16 bits, 2 channels, 8 kHz */
+               if (runtime->channels > 2)
+                       set_dac_channels(cm, rec, 2);
+               spin_lock_irq(&cm->reg_lock);
+               val = snd_cmipci_read(cm, CM_REG_FUNCTRL1);
+               val &= ~(CM_ASFC_MASK << (rec->ch * 3));
+               val |= (4 << CM_ASFC_SHIFT) << (rec->ch * 3);
+               snd_cmipci_write(cm, CM_REG_FUNCTRL1, val);
+               val = snd_cmipci_read(cm, CM_REG_CHFORMAT);
+               val &= ~(CM_CH0FMT_MASK << (rec->ch * 2));
+               val |= (3 << CM_CH0FMT_SHIFT) << (rec->ch * 2);
+               if (cm->chip_version == 68) {
+                       val &= ~(CM_CH0_SRATE_88K << (rec->ch * 2));
+                       val &= ~(CM_CH0_SRATE_96K << (rec->ch * 2));
+               }
+               snd_cmipci_write(cm, CM_REG_CHFORMAT, val);
+       
+               /* start stream (we don't need interrupts) */
+               cm->ctrl |= CM_CHEN0 << rec->ch;
+               snd_cmipci_write(cm, CM_REG_FUNCTRL0, cm->ctrl);
+               spin_unlock_irq(&cm->reg_lock);
+
+               msleep(1);
+
+               /* stop and reset stream */
+               spin_lock_irq(&cm->reg_lock);
+               cm->ctrl &= ~(CM_CHEN0 << rec->ch);
+               val = CM_RST_CH0 << rec->ch;
+               snd_cmipci_write(cm, CM_REG_FUNCTRL0, cm->ctrl | val);
+               snd_cmipci_write(cm, CM_REG_FUNCTRL0, cm->ctrl & ~val);
+               spin_unlock_irq(&cm->reg_lock);
+
+               rec->needs_silencing = 0;
+       }
+}
+
 static int snd_cmipci_playback_hw_free(struct snd_pcm_substream *substream)
 {
        struct cmipci *cm = snd_pcm_substream_chip(substream);
        setup_spdif_playback(cm, substream, 0, 0);
        restore_mixer_state(cm);
+       snd_cmipci_silence_hack(cm, &cm->channel[0]);
+       return snd_cmipci_hw_free(substream);
+}
+
+static int snd_cmipci_playback2_hw_free(struct snd_pcm_substream *substream)
+{
+       struct cmipci *cm = snd_pcm_substream_chip(substream);
+       snd_cmipci_silence_hack(cm, &cm->channel[1]);
        return snd_cmipci_hw_free(substream);
 }
 
@@ -1736,7 +1802,7 @@ static struct snd_pcm_ops snd_cmipci_playback2_ops = {
        .close =        snd_cmipci_playback2_close,
        .ioctl =        snd_pcm_lib_ioctl,
        .hw_params =    snd_cmipci_playback2_hw_params,
-       .hw_free =      snd_cmipci_hw_free,
+       .hw_free =      snd_cmipci_playback2_hw_free,
        .prepare =      snd_cmipci_capture_prepare,     /* channel B */
        .trigger =      snd_cmipci_capture_trigger,     /* channel B */
        .pointer =      snd_cmipci_capture_pointer,     /* channel B */