ASoC: max9867: Implement exact integer mode

For 8kHz and 16kHz sample rates and certain PCLK values
the codec can be programmed to operate in exact integer
mode. If available, use it to achieve the exact sample rate.
Signed-off-by: Pavel Dobias <dobias@2n.com>
Link: https://lore.kernel.org/r/20221123153818.24650-1-dobias@2n.comSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/codecs/max9867.c

@@ -323,7 +323,7 @@ static int max9867_startup(struct snd_pcm_substream *substream,
 static int max9867_dai_hw_params(struct snd_pcm_substream *substream,
 		struct snd_pcm_hw_params *params, struct snd_soc_dai *dai)
 {
-	int value;
+	int value, freq = 0;
 	unsigned long int rate, ratio;
 	struct snd_soc_component *component = dai->component;
 	struct max9867_priv *max9867 = snd_soc_component_get_drvdata(component);
@@ -373,6 +373,35 @@ static int max9867_dai_hw_params(struct snd_pcm_substream *substream,
 		}
 		regmap_update_bits(max9867->regmap, MAX9867_IFC1B,
 			MAX9867_IFC1B_BCLK_MASK, value);
+
+		/* Exact integer mode available for 8kHz and 16kHz sample rates
+		 * and certain PCLK (prescaled MCLK) values.
+		 */
+		if (params_rate(params) == 8000 ||
+		    params_rate(params) == 16000) {
+			switch (max9867->pclk) {
+			case 12000000:
+				freq = 0x08;
+				break;
+			case 13000000:
+				freq = 0x0A;
+				break;
+			case 16000000:
+				freq = 0x0C;
+				break;
+			case 19200000:
+				freq = 0x0E;
+				break;
+			}
+		}
+		if (freq && params_rate(params) == 16000)
+			freq++;
+
+		/* If exact integer mode not available, the freq value
+		 * remains zero, i.e. normal mode is used.
+		 */
+		regmap_update_bits(max9867->regmap, MAX9867_SYSCLK,
+				   MAX9867_FREQ_MASK, freq);
 	} else {
 		/*
 		 * digital pll locks on to any externally supplied LRCLK signal
@@ -428,8 +457,6 @@ static int max9867_set_dai_sysclk(struct snd_soc_dai *codec_dai,
 			 freq);
 	max9867->sysclk = freq;
 	value = value << MAX9867_PSCLK_SHIFT;
-	/* exact integer mode is not supported */
-	value &= ~MAX9867_FREQ_MASK;
 	regmap_update_bits(max9867->regmap, MAX9867_SYSCLK,
 			MAX9867_PSCLK_MASK, value);
 	return 0;