ASoC: davinci-mcasp: Add rule to constrain the minimum period size

The minimum period size (in frames) must be not lower than the FIFO size
of McASP and in general too small period size would easily result underrun
in applications as eDMA - the most common DMA servicing McASP have support
for limited number of periods.
Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/davinci/davinci-mcasp.c

@@ -1242,6 +1242,20 @@ static int davinci_mcasp_hw_rule_format(struct snd_pcm_hw_params *params,
 	return snd_mask_refine(fmt, &nfmt);
 }
 
+static int davinci_mcasp_hw_rule_min_periodsize(
+		struct snd_pcm_hw_params *params, struct snd_pcm_hw_rule *rule)
+{
+	struct snd_interval *period_size = hw_param_interval(params,
+						SNDRV_PCM_HW_PARAM_PERIOD_SIZE);
+	struct snd_interval frames;
+
+	snd_interval_any(&frames);
+	frames.min = 64;
+	frames.integer = 1;
+
+	return snd_interval_refine(period_size, &frames);
+}
+
 static int davinci_mcasp_startup(struct snd_pcm_substream *substream,
 				 struct snd_soc_dai *cpu_dai)
 {
@@ -1333,6 +1347,11 @@ static int davinci_mcasp_startup(struct snd_pcm_substream *substream,
 			return ret;
 	}
 
+	snd_pcm_hw_rule_add(substream->runtime, 0,
+			    SNDRV_PCM_HW_PARAM_PERIOD_SIZE,
+			    davinci_mcasp_hw_rule_min_periodsize, NULL,
+			    SNDRV_PCM_HW_PARAM_PERIOD_SIZE, -1);
+
 	return 0;
 }