[v5] ASoC: qcom: lpass-cpu: Fix pop noise during audio capture begin

[Judy Hsiao <judyhsiao@chromium.org>]

From: Srinivasa Rao Mandadapu <srivasam@codeaurora.org>

This patch fixes PoP noise of around 15ms observed during audio
capture begin.
Enables BCLK and LRCLK in snd_soc_dai_ops prepare call for
introducing some delay before capture start.

Co-developed-by: Judy Hsiao <judyhsiao@chromium.org>
Signed-off-by: Judy Hsiao <judyhsiao@chromium.org>
Signed-off-by: Srinivasa Rao Mandadapu <srivasam@codeaurora.org>
(am from https://patchwork.kernel.org/patch/12276369/)
(also found at https://lore.kernel.org/r/20210524142114.18676-1-srivasam@codeaurora.org)

---
Changes Since V4:
        -- Replaced the __clk_is_enabled(BCLK) check by the self maintained 
           mi2s_was_prepared bool state.
        -- Removed unrelated changes.
        -- Refined comments.
Changes Since V3:
        -- Checked BCLK is off before enabling it in lpass_cpu_daiops_prepare as
           lpass_cpu_daiops_prepare can be called multiple times
        -- Checked BCLK is on before disabling it in lpass_cpu_daiops_shutdown to
           fix the WARN. It is because BCLK may not be enabled if
           lpass_cpu_daiops_prepare is not called before lpass_cpu_daiops_shutdown
        -- Added more comments
Changes Since V2:
        -- Updated comments as per linux style
        -- Removed unrelated changes
Changes Since V1:
        -- Enabled BCLK and LRCLK in dai ops prepare API instead of startup API
        -- Added comments

 sound/soc/qcom/lpass-cpu.c | 80 ++++++++++++++++++++++++++++++++++++++
 sound/soc/qcom/lpass.h     |  4 ++
 2 files changed, 84 insertions(+)

diff --git a/sound/soc/qcom/lpass-cpu.c b/sound/soc/qcom/lpass-cpu.c
index af8cb64924a0..3129e7cc25a4 100644
--- a/sound/soc/qcom/lpass-cpu.c
+++ b/sound/soc/qcom/lpass-cpu.c
@@ -93,8 +93,30 @@ static void lpass_cpu_daiops_shutdown(struct snd_pcm_substream *substream,
 		struct snd_soc_dai *dai)
 {
 	struct lpass_data *drvdata = snd_soc_dai_get_drvdata(dai);
+	struct lpaif_i2sctl *i2sctl = drvdata->i2sctl;
+	unsigned int id = dai->driver->id;
 
 	clk_disable_unprepare(drvdata->mi2s_osr_clk[dai->driver->id]);
+	/*
+	 * Ensure LRCLK is disabled even in device node validation.
+	 * Will not impact if disabled in lpass_cpu_daiops_trigger()
+	 * suspend.
+	 */
+	if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK)
+		regmap_fields_write(i2sctl->spken, id, LPAIF_I2SCTL_SPKEN_DISABLE);
+	else
+		regmap_fields_write(i2sctl->micen, id, LPAIF_I2SCTL_MICEN_DISABLE);
+
+	/*
+	 * BCLK may not be enabled if lpass_cpu_daiops_prepare is called before
+	 * lpass_cpu_daiops_shutdown. It's paired with the clk_enable in
+	 * lpass_cpu_daiops_prepare.
+	 */
+	if (drvdata->mi2s_was_prepared[dai->driver->id]) {
+		drvdata->mi2s_was_prepared[dai->driver->id] = false;
+		clk_disable(drvdata->mi2s_bit_clk[dai->driver->id]);
+	}
+
 	clk_unprepare(drvdata->mi2s_bit_clk[dai->driver->id]);
 }
 
@@ -275,6 +297,18 @@ static int lpass_cpu_daiops_trigger(struct snd_pcm_substream *substream,
 	case SNDRV_PCM_TRIGGER_START:
 	case SNDRV_PCM_TRIGGER_RESUME:
 	case SNDRV_PCM_TRIGGER_PAUSE_RELEASE:
+		/*
+		 * Ensure lpass BCLK/LRCLK is enabled during
+		 * device resume as lpass_cpu_daiops_prepare() is not called
+		 * after the device resumes. We don't check mi2s_was_prepared before
+		 * enable/disable BCLK in trigger events because:
+		 *  1. These trigger events are paired, so the BCLK
+		 *     enable_count is balanced.
+		 *  2. the BCLK can be shared (ex: headset and headset mic),
+		 *     we need to increase the enable_count so that we don't
+		 *     turn off the shared BCLK while other devices are using
+		 *     it.
+		 */
 		if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK) {
 			ret = regmap_fields_write(i2sctl->spken, id,
 						 LPAIF_I2SCTL_SPKEN_ENABLE);
@@ -296,6 +330,10 @@ static int lpass_cpu_daiops_trigger(struct snd_pcm_substream *substream,
 	case SNDRV_PCM_TRIGGER_STOP:
 	case SNDRV_PCM_TRIGGER_SUSPEND:
 	case SNDRV_PCM_TRIGGER_PAUSE_PUSH:
+		/*
+		 * To ensure lpass BCLK/LRCLK is disabled during
+		 * device suspend.
+		 */
 		if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK) {
 			ret = regmap_fields_write(i2sctl->spken, id,
 						 LPAIF_I2SCTL_SPKEN_DISABLE);
@@ -315,12 +353,54 @@ static int lpass_cpu_daiops_trigger(struct snd_pcm_substream *substream,
 	return ret;
 }
 
+static int lpass_cpu_daiops_prepare(struct snd_pcm_substream *substream,
+		struct snd_soc_dai *dai)
+{
+	struct lpass_data *drvdata = snd_soc_dai_get_drvdata(dai);
+	struct lpaif_i2sctl *i2sctl = drvdata->i2sctl;
+	unsigned int id = dai->driver->id;
+	int ret;
+	/*
+	 * Ensure lpass BCLK/LRCLK is enabled bit before playback/capture
+	 * data flow starts. This allows other codec to have some delay before
+	 * the data flow.
+	 * (ex: to drop start up pop noise before capture starts).
+	 */
+	if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK)
+		ret = regmap_fields_write(i2sctl->spken, id, LPAIF_I2SCTL_SPKEN_ENABLE);
+	else
+		ret = regmap_fields_write(i2sctl->micen, id, LPAIF_I2SCTL_MICEN_ENABLE);
+
+	if (ret) {
+		dev_err(dai->dev, "error writing to i2sctl reg: %d\n", ret);
+		return ret;
+	}
+
+	/*
+	 * Check mi2s_was_prepared before enabling BCLK as lpass_cpu_daiops_prepare can
+	 * be called multiple times. It's paired with the clk_disable in
+	 * lpass_cpu_daiops_shutdown.
+	 */
+	if (!drvdata->mi2s_was_prepared[dai->driver->id]) {
+		drvdata->mi2s_was_prepared[dai->driver->id] = true;
+		ret = clk_enable(drvdata->mi2s_bit_clk[id]);
+		if (ret) {
+			dev_err(dai->dev, "error in enabling mi2s bit clk: %d\n", ret);
+			clk_disable(drvdata->mi2s_osr_clk[id]);
+			drvdata->mi2s_was_prepared[dai->driver->id] = false;
+			return ret;
+		}
+	}
+	return 0;
+}
+
 const struct snd_soc_dai_ops asoc_qcom_lpass_cpu_dai_ops = {
 	.set_sysclk	= lpass_cpu_daiops_set_sysclk,
 	.startup	= lpass_cpu_daiops_startup,
 	.shutdown	= lpass_cpu_daiops_shutdown,
 	.hw_params	= lpass_cpu_daiops_hw_params,
 	.trigger	= lpass_cpu_daiops_trigger,
+	.prepare	= lpass_cpu_daiops_prepare,
 };
 EXPORT_SYMBOL_GPL(asoc_qcom_lpass_cpu_dai_ops);
 
diff --git a/sound/soc/qcom/lpass.h b/sound/soc/qcom/lpass.h
index 83b2e08ade06..7f72214404ba 100644
--- a/sound/soc/qcom/lpass.h
+++ b/sound/soc/qcom/lpass.h
@@ -67,6 +67,10 @@ struct lpass_data {
 	/* MI2S SD lines to use for playback/capture */
 	unsigned int mi2s_playback_sd_mode[LPASS_MAX_MI2S_PORTS];
 	unsigned int mi2s_capture_sd_mode[LPASS_MAX_MI2S_PORTS];
+
+	/* The state of MI2S prepare dai_ops was called */
+	bool mi2s_was_prepared[LPASS_MAX_MI2S_PORTS];
+
 	int hdmi_port_enable;
 
 	/* low-power audio interface (LPAIF) registers */
-- 
2.31.0