ASoC: nau8540: Implement hw constraint for rates

nau8540 driver restricts the sample rate with over sampling rate, but
currently it barely bails out at hw_params with -EINVAL error (with a
kernel message); this doesn't help for user-space to recognize which
rate can be actually used.

This patch introduces the proper hw constraint for adjusting the
available range of the sample rate depending on the OSR setup, as well
as some code cleanup, for improving the communication with
user-space.  Now applications can know the valid rate beforehand and
reduces the rate appropriately without errors.
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Link: https://lore.kernel.org/r/20220823081000.2965-6-tiwai@suse.deSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/codecs/nau8540.c

@@ -357,17 +357,32 @@ static const struct snd_soc_dapm_route nau8540_dapm_routes[] = {
 	{"AIFTX", NULL, "Digital CH4 Mux"},
 };
 
-static int nau8540_clock_check(struct nau8540 *nau8540, int rate, int osr)
+static const struct nau8540_osr_attr *
+nau8540_get_osr(struct nau8540 *nau8540)
 {
+	unsigned int osr;
+
+	regmap_read(nau8540->regmap, NAU8540_REG_ADC_SAMPLE_RATE, &osr);
+	osr &= NAU8540_ADC_OSR_MASK;
 	if (osr >= ARRAY_SIZE(osr_adc_sel))
-		return -EINVAL;
+		return NULL;
+	return &osr_adc_sel[osr];
+}
+
+static int nau8540_dai_startup(struct snd_pcm_substream *substream,
+			       struct snd_soc_dai *dai)
+{
+	struct snd_soc_component *component = dai->component;
+	struct nau8540 *nau8540 = snd_soc_component_get_drvdata(component);
+	const struct nau8540_osr_attr *osr;
 
-	if (rate * osr > CLK_ADC_MAX) {
-		dev_err(nau8540->dev, "exceed the maximum frequency of CLK_ADC\n");
+	osr = nau8540_get_osr(nau8540);
+	if (!osr || !osr->osr)
 		return -EINVAL;
-	}
 
-	return 0;
+	return snd_pcm_hw_constraint_minmax(substream->runtime,
+					    SNDRV_PCM_HW_PARAM_RATE,
+					    0, CLK_ADC_MAX / osr->osr);
 }
 
 static int nau8540_hw_params(struct snd_pcm_substream *substream,
@@ -375,7 +390,8 @@ static int nau8540_hw_params(struct snd_pcm_substream *substream,
 {
 	struct snd_soc_component *component = dai->component;
 	struct nau8540 *nau8540 = snd_soc_component_get_drvdata(component);
-	unsigned int val_len = 0, osr;
+	unsigned int val_len = 0;
+	const struct nau8540_osr_attr *osr;
 
 	/* CLK_ADC = OSR * FS
 	 * ADC clock frequency is defined as Over Sampling Rate (OSR)
@@ -383,13 +399,14 @@ static int nau8540_hw_params(struct snd_pcm_substream *substream,
 	 * values must be selected such that the maximum frequency is less
 	 * than 6.144 MHz.
 	 */
-	regmap_read(nau8540->regmap, NAU8540_REG_ADC_SAMPLE_RATE, &osr);
-	osr &= NAU8540_ADC_OSR_MASK;
-	if (nau8540_clock_check(nau8540, params_rate(params), osr))
+	osr = nau8540_get_osr(nau8540);
+	if (!osr || !osr->osr)
+		return -EINVAL;
+	if (params_rate(params) * osr->osr > CLK_ADC_MAX)
 		return -EINVAL;
 	regmap_update_bits(nau8540->regmap, NAU8540_REG_CLOCK_SRC,
 		NAU8540_CLK_ADC_SRC_MASK,
-		osr_adc_sel[osr].clk_src << NAU8540_CLK_ADC_SRC_SFT);
+		osr->clk_src << NAU8540_CLK_ADC_SRC_SFT);
 
 	switch (params_width(params)) {
 	case 16:
@@ -515,6 +532,7 @@ static int nau8540_set_tdm_slot(struct snd_soc_dai *dai,
 
 
 static const struct snd_soc_dai_ops nau8540_dai_ops = {
+	.startup = nau8540_dai_startup,
 	.hw_params = nau8540_hw_params,
 	.set_fmt = nau8540_set_fmt,
 	.set_tdm_slot = nau8540_set_tdm_slot,