ASoC: kirkwood: implement NO_PERIOD_WAKEUP support

Permit ALSA to run without hardware interrupts from the audio interface.
Instead, ALSA will use a kernel timer to decide when to check the buffer
state, resulting in a lighter workload for the CPU.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Tested-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Mark Brown <broonie@linaro.org>

sound/soc/kirkwood/kirkwood-dma.c

@@ -28,11 +28,12 @@ static struct kirkwood_dma_data *kirkwood_priv(struct snd_pcm_substream *subs)
 }
 
 static struct snd_pcm_hardware kirkwood_dma_snd_hw = {
-	.info = (SNDRV_PCM_INFO_INTERLEAVED |
-		 SNDRV_PCM_INFO_MMAP |
-		 SNDRV_PCM_INFO_MMAP_VALID |
-		 SNDRV_PCM_INFO_BLOCK_TRANSFER |
-		 SNDRV_PCM_INFO_PAUSE),
+	.info = SNDRV_PCM_INFO_INTERLEAVED |
+		SNDRV_PCM_INFO_MMAP |
+		SNDRV_PCM_INFO_MMAP_VALID |
+		SNDRV_PCM_INFO_BLOCK_TRANSFER |
+		SNDRV_PCM_INFO_PAUSE |
+		SNDRV_PCM_INFO_NO_PERIOD_WAKEUP,
 	.buffer_bytes_max	= KIRKWOOD_SND_MAX_BUFFER_BYTES,
 	.period_bytes_min	= KIRKWOOD_SND_MIN_PERIOD_BYTES,
 	.period_bytes_max	= KIRKWOOD_SND_MAX_PERIOD_BYTES,

sound/soc/kirkwood/kirkwood-i2s.c

@@ -234,6 +234,7 @@ static unsigned kirkwood_i2s_play_mute(unsigned ctl)
 static int kirkwood_i2s_play_trigger(struct snd_pcm_substream *substream,
 				int cmd, struct snd_soc_dai *dai)
 {
+	struct snd_pcm_runtime *runtime = substream->runtime;
 	struct kirkwood_dma_data *priv = snd_soc_dai_get_drvdata(dai);
 	uint32_t ctl, value;
 
@@ -271,9 +272,11 @@ static int kirkwood_i2s_play_trigger(struct snd_pcm_substream *substream,
 		writel(value, priv->io + KIRKWOOD_PLAYCTL);
 
 		/* enable interrupts */
-		value = readl(priv->io + KIRKWOOD_INT_MASK);
-		value |= KIRKWOOD_INT_CAUSE_PLAY_BYTES;
-		writel(value, priv->io + KIRKWOOD_INT_MASK);
+		if (!runtime->no_period_wakeup) {
+			value = readl(priv->io + KIRKWOOD_INT_MASK);
+			value |= KIRKWOOD_INT_CAUSE_PLAY_BYTES;
+			writel(value, priv->io + KIRKWOOD_INT_MASK);
+		}
 
 		/* enable playback */
 		writel(ctl, priv->io + KIRKWOOD_PLAYCTL);