+/*
+ * 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;
+ }
+}
+