forked from Minki/linux
ALSA: snd-aloop - improve the sample copy accurracy
Maintain both streams (playback, capture) synchronized. Previous code didn't take in account the small byte count drifts caused by the irq position rounding. Signed-off-by: Jaroslav Kysela <perex@perex.cz> Signed-off-by: Takashi Iwai <tiwai@suse.de>
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b012513c66
@ -117,6 +117,7 @@ struct loopback_pcm {
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/* timer stuff */
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unsigned int irq_pos; /* fractional IRQ position */
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unsigned int period_size_frac;
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unsigned int last_drift;
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unsigned long last_jiffies;
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struct timer_list timer;
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};
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@ -264,6 +265,7 @@ static int loopback_trigger(struct snd_pcm_substream *substream, int cmd)
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return err;
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dpcm->last_jiffies = jiffies;
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dpcm->pcm_rate_shift = 0;
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dpcm->last_drift = 0;
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spin_lock(&cable->lock);
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cable->running |= stream;
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cable->pause &= ~stream;
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@ -444,34 +446,30 @@ static void copy_play_buf(struct loopback_pcm *play,
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}
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}
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#define BYTEPOS_UPDATE_POSONLY 0
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#define BYTEPOS_UPDATE_CLEAR 1
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#define BYTEPOS_UPDATE_COPY 2
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static void loopback_bytepos_update(struct loopback_pcm *dpcm,
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unsigned int delta,
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unsigned int cmd)
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static inline unsigned int bytepos_delta(struct loopback_pcm *dpcm,
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unsigned int jiffies_delta)
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{
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unsigned int count;
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unsigned long last_pos;
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unsigned int delta;
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last_pos = byte_pos(dpcm, dpcm->irq_pos);
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dpcm->irq_pos += delta * dpcm->pcm_bps;
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count = byte_pos(dpcm, dpcm->irq_pos) - last_pos;
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if (!count)
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return;
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if (cmd == BYTEPOS_UPDATE_CLEAR)
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clear_capture_buf(dpcm, count);
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else if (cmd == BYTEPOS_UPDATE_COPY)
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copy_play_buf(dpcm->cable->streams[SNDRV_PCM_STREAM_PLAYBACK],
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dpcm->cable->streams[SNDRV_PCM_STREAM_CAPTURE],
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count);
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dpcm->buf_pos += count;
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dpcm->buf_pos %= dpcm->pcm_buffer_size;
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dpcm->irq_pos += jiffies_delta * dpcm->pcm_bps;
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delta = byte_pos(dpcm, dpcm->irq_pos) - last_pos;
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if (delta >= dpcm->last_drift)
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delta -= dpcm->last_drift;
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dpcm->last_drift = 0;
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if (dpcm->irq_pos >= dpcm->period_size_frac) {
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dpcm->irq_pos %= dpcm->period_size_frac;
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dpcm->period_update_pending = 1;
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}
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return delta;
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}
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static inline void bytepos_finish(struct loopback_pcm *dpcm,
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unsigned int delta)
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{
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dpcm->buf_pos += delta;
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dpcm->buf_pos %= dpcm->pcm_buffer_size;
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}
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static unsigned int loopback_pos_update(struct loopback_cable *cable)
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@ -481,7 +479,7 @@ static unsigned int loopback_pos_update(struct loopback_cable *cable)
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struct loopback_pcm *dpcm_capt =
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cable->streams[SNDRV_PCM_STREAM_CAPTURE];
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unsigned long delta_play = 0, delta_capt = 0;
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unsigned int running;
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unsigned int running, count1, count2;
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unsigned long flags;
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spin_lock_irqsave(&cable->lock, flags);
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@ -500,12 +498,13 @@ static unsigned int loopback_pos_update(struct loopback_cable *cable)
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goto unlock;
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if (delta_play > delta_capt) {
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loopback_bytepos_update(dpcm_play, delta_play - delta_capt,
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BYTEPOS_UPDATE_POSONLY);
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count1 = bytepos_delta(dpcm_play, delta_play - delta_capt);
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bytepos_finish(dpcm_play, count1);
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delta_play = delta_capt;
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} else if (delta_play < delta_capt) {
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loopback_bytepos_update(dpcm_capt, delta_capt - delta_play,
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BYTEPOS_UPDATE_CLEAR);
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count1 = bytepos_delta(dpcm_capt, delta_capt - delta_play);
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clear_capture_buf(dpcm_capt, count1);
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bytepos_finish(dpcm_capt, count1);
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delta_capt = delta_play;
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}
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@ -513,8 +512,17 @@ static unsigned int loopback_pos_update(struct loopback_cable *cable)
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goto unlock;
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/* note delta_capt == delta_play at this moment */
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loopback_bytepos_update(dpcm_capt, delta_capt, BYTEPOS_UPDATE_COPY);
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loopback_bytepos_update(dpcm_play, delta_play, BYTEPOS_UPDATE_POSONLY);
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count1 = bytepos_delta(dpcm_play, delta_play);
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count2 = bytepos_delta(dpcm_capt, delta_capt);
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if (count1 < count2) {
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dpcm_capt->last_drift = count2 - count1;
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count1 = count2;
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} else if (count1 > count2) {
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dpcm_play->last_drift = count1 - count2;
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}
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copy_play_buf(dpcm_play, dpcm_capt, count1);
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bytepos_finish(dpcm_play, count1);
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bytepos_finish(dpcm_capt, count1);
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unlock:
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spin_unlock_irqrestore(&cable->lock, flags);
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return running;
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