[ALSA] snd-dummy - better realtime app support

when the time interval for a period is smaller than kernel HZ, then
snd-aloop and snd-dummy cannot call snd_pcm_period_elapsed as fast enough
annymore. this happens for example with games. but the app still needs to
see, that the buffer actually did go further, which is provided by these
patches.

Signed-off-by: Ahmet İnan <ainan <at> mathematik.uni-freiburg.de>
Signed-off-by: NTakashi Iwai <tiwai@suse.de>

sound/drivers/dummy.c

@@ -259,10 +259,10 @@ static void snd_card_dummy_pcm_timer_function(unsigned long data)
 	dpcm->timer.expires = 1 + jiffies;
 	add_timer(&dpcm->timer);
 	dpcm->pcm_irq_pos += dpcm->pcm_bps;
+	dpcm->pcm_buf_pos += dpcm->pcm_bps;
+	dpcm->pcm_buf_pos %= dpcm->pcm_buffer_size * dpcm->pcm_hz;
 	if (dpcm->pcm_irq_pos >= dpcm->pcm_period_size * dpcm->pcm_hz) {
 		dpcm->pcm_irq_pos %= dpcm->pcm_period_size * dpcm->pcm_hz;
-		dpcm->pcm_buf_pos += dpcm->pcm_period_size;
-		dpcm->pcm_buf_pos %= dpcm->pcm_buffer_size;
 		spin_unlock_irqrestore(&dpcm->lock, flags);
 		snd_pcm_period_elapsed(dpcm->substream);
 	} else
@@ -274,7 +274,7 @@ static snd_pcm_uframes_t snd_card_dummy_pcm_pointer(struct snd_pcm_substream *su
 	struct snd_pcm_runtime *runtime = substream->runtime;
 	struct snd_dummy_pcm *dpcm = runtime->private_data;
 
-	return bytes_to_frames(runtime, dpcm->pcm_buf_pos);
+	return bytes_to_frames(runtime, dpcm->pcm_buf_pos / dpcm->pcm_hz);
 }
 
 static struct snd_pcm_hardware snd_card_dummy_playback =