[alsa-devel] [RFC PATCH 5/5] ASoC: omap-mcbsp: Place correct constraints for streams

[Peter Ujfalusi]

OMAP McBSP FIFO is word structured:
McBSP2 has 1024 + 256 = 1280 word long buffer,
McBSP1,3,4,5 has 128 word long buffer

This means, that the size of the FIFO
depends on the McBSP word size configuration.
For example on McBSP3:
16bit samples: size is 128 * 2 = 256 bytes
32bit samples: size is 128 * 4 = 512 bytes
It is simpler to place constraint for buffer and period based on channels.
McBSP3 as example again (16 or 32 bit samples):
1 channel (mono): size is 128 frames (128 words)
2 channels (stereo): size is 128 / 2 = 64 frames (2 * 64 words)
4 channels: size is 128 / 4 = 32 frames (4 * 32 words)

Use the second method to place hw_rule on buffer size, and in threshold
mode to period size.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi at nokia.com>
---
 sound/soc/omap/omap-mcbsp.c |   98 +++++++++++++++++++++++++++++++++---------
 1 files changed, 77 insertions(+), 21 deletions(-)

diff --git a/sound/soc/omap/omap-mcbsp.c b/sound/soc/omap/omap-mcbsp.c
index b06d8f1..d6ed761 100644
--- a/sound/soc/omap/omap-mcbsp.c
+++ b/sound/soc/omap/omap-mcbsp.c
@@ -173,6 +173,52 @@ static void omap_mcbsp_set_threshold(struct snd_pcm_substream *substream)
 		omap_mcbsp_set_rx_threshold(mcbsp_data->bus_id, words);
 }
 
+static int hw_rule_bsize_by_channels(struct snd_pcm_hw_params *params,
+				    struct snd_pcm_hw_rule *rule)
+{
+	struct snd_interval *bs = hw_param_interval(params,
+					SNDRV_PCM_HW_PARAM_BUFFER_SIZE);
+	struct snd_interval *c = hw_param_interval(params,
+					SNDRV_PCM_HW_PARAM_CHANNELS);
+	struct omap_mcbsp_data *mcbsp_data = rule->private;
+	struct snd_interval frames;
+	int size;
+
+	snd_interval_any(&frames);
+	size = omap_mcbsp_get_fifo_size(mcbsp_data->bus_id);
+
+	frames.min = size / c->min;
+	frames.integer = 1;
+	return snd_interval_refine(bs, &frames);
+
+}
+
+static int hw_rule_psize_by_channels(struct snd_pcm_hw_params *params,
+				    struct snd_pcm_hw_rule *rule)
+{
+	struct snd_interval *ps = hw_param_interval(params,
+					SNDRV_PCM_HW_PARAM_PERIOD_SIZE);
+	struct snd_interval *c = hw_param_interval(params,
+					SNDRV_PCM_HW_PARAM_CHANNELS);
+	struct snd_pcm_substream *substream = rule->private;
+	struct snd_soc_pcm_runtime *rtd = substream->private_data;
+	struct snd_soc_dai *cpu_dai = rtd->dai->cpu_dai;
+	struct omap_mcbsp_data *mcbsp_data = to_mcbsp(cpu_dai->private_data);
+	struct snd_interval frames;
+	int size;
+
+	snd_interval_any(&frames);
+	if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK)
+		size = omap_mcbsp_get_max_tx_threshold(mcbsp_data->bus_id);
+	else
+		size = omap_mcbsp_get_max_rx_threshold(mcbsp_data->bus_id);
+
+	frames.min = 8;
+	frames.max = size / c->min;
+	frames.integer = 1;
+	return snd_interval_refine(ps, &frames);
+}
+
 static int omap_mcbsp_dai_startup(struct snd_pcm_substream *substream,
 				  struct snd_soc_dai *dai)
 {
@@ -185,33 +231,43 @@ static int omap_mcbsp_dai_startup(struct snd_pcm_substream *substream,
 	if (!cpu_dai->active)
 		err = omap_mcbsp_request(bus_id);
 
+	/*
+	 * OMAP McBSP FIFO is word structured.
+	 * McBSP2 has 1024 + 256 = 1280 word long buffer,
+	 * McBSP1,3,4,5 has 128 word long buffer
+	 * This means that the size of the FIFO depends on the sample format.
+	 * For example on McBSP3:
+	 * 16bit samples: size is 128 * 2 = 256 bytes
+	 * 32bit samples: size is 128 * 4 = 512 bytes
+	 * It is simpler to place constraint for buffer and period based on
+	 * channels.
+	 * McBSP3 as example again (16 or 32 bit samples):
+	 * 1 channel (mono): size is 128 frames (128 words)
+	 * 2 channels (stereo): size is 128 / 2 = 64 frames (2 * 64 words)
+	 * 4 channels: size is 128 / 4 = 32 frames (4 * 32 words)
+	 */
+
+	/*
+	 * The first rule is for the buffer size, we should not allow smaller
+	 * buffer than the FIFO size to avoid underruns
+	 */
+	snd_pcm_hw_rule_add(substream->runtime, 0, SNDRV_PCM_HW_PARAM_CHANNELS,
+				    hw_rule_bsize_by_channels, mcbsp_data,
+				    SNDRV_PCM_HW_PARAM_BUFFER_SIZE, -1);
+
 	if (cpu_is_omap343x()) {
 		int dma_op_mode = omap_mcbsp_get_dma_op_mode(bus_id);
-		int max_period;
 
 		/*
-		 * McBSP2 in OMAP3 has 1024 * 32-bit internal audio buffer.
-		 * Set constraint for minimum buffer size to the same than FIFO
-		 * size in order to avoid underruns in playback startup because
-		 * HW is keeping the DMA request active until FIFO is filled.
+		 * In case os threshold mode, the rule will ensure, that the
+		 * period size is not bigger than the maximum allowed threshold
+		 * value.
 		 */
-		if (bus_id == 1)
-			snd_pcm_hw_constraint_minmax(substream->runtime,
-					SNDRV_PCM_HW_PARAM_BUFFER_BYTES,
-					4096, UINT_MAX);
-
-		if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK)
-			max_period = omap_mcbsp_get_max_tx_threshold(bus_id);
-		else
-			max_period = omap_mcbsp_get_max_rx_threshold(bus_id);
-
-		max_period++;
-		max_period <<= 1;
-
 		if (dma_op_mode == MCBSP_DMA_MODE_THRESHOLD)
-			snd_pcm_hw_constraint_minmax(substream->runtime,
-						SNDRV_PCM_HW_PARAM_PERIOD_BYTES,
-						32, max_period);
+			snd_pcm_hw_rule_add(substream->runtime, 0,
+					SNDRV_PCM_HW_PARAM_CHANNELS,
+					hw_rule_psize_by_channels, substream,
+					SNDRV_PCM_HW_PARAM_PERIOD_SIZE, -1);
 	}
 
 	return err;
-- 
1.7.1