ASoC: SOF: imx8m: Add runtime PM / System PM support

We make use of common imx8m_suspend / imx8m_resume functions
for both system PM and runtime PM.

imx8m_suspend:
	- frees the MU channels
	- disables the clocks

imx8m_resume
	- enables the clocks
	- requests the MU channels

On i.MX8MP there is no dedicated functionality to put the DSP in reset.
The only way of doing this is to POWER DOWN the Audiomix domain.

We are able to do this because turning off the clocks and freeing the
channels makes the Audiomix to have no users thus PM kernel core turns
it down.

SOF core will not call system PM suspend handler if the DSP is already
down, but at resume it will call the system PM resume. So, we need to
keep track of the state via snd_sof_dsp_set_power_state

Few insights on how SOF core handles the PM:
 - SOF core uses PM runtime autosuspend (with a timeout of 2 secs)
 - at probe, SOF core boots the DSP and lets the PM runtime suspend to
   turn it off, if there is no activity
 - when someone opens the ALSA sound card (aplay/arecord, etc) ALSA core
   calls PM runtime resume to turn on the DSP
 - when the ALSA sound card is closed SOF core make use of PM subsystem
  to call PM runtime suspend and thus turning off the DSP.

Signed-off-by: Daniel Baluta <daniel.baluta@nxp.com>
Reviewed-by: Ranjani Sridharan <ranjani.sridharan@linux.intel.com>
Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20211119094319.81674-4-daniel.baluta@oss.nxp.com
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/sof/imx/imx8m.c

@@ -195,7 +195,9 @@ static int imx8m_probe(struct snd_sof_dev *sdev)
 	if (ret < 0)
 		goto exit_pdev_unregister;
 
-	imx8_enable_clocks(sdev, priv->clks);
+	ret = imx8_enable_clocks(sdev, priv->clks);
+	if (ret < 0)
+		goto exit_pdev_unregister;
 
 	return 0;
 
@@ -252,6 +254,100 @@ static struct snd_soc_dai_driver imx8m_dai[] = {
 },
 };
 
+static int imx8m_dsp_set_power_state(struct snd_sof_dev *sdev,
+				     const struct sof_dsp_power_state *target_state)
+{
+	sdev->dsp_power_state = *target_state;
+
+	return 0;
+}
+
+static int imx8m_resume(struct snd_sof_dev *sdev)
+{
+	struct imx8m_priv *priv = (struct imx8m_priv *)sdev->pdata->hw_pdata;
+	int ret;
+	int i;
+
+	ret = imx8_enable_clocks(sdev, priv->clks);
+	if (ret < 0)
+		return ret;
+
+	for (i = 0; i < DSP_MU_CHAN_NUM; i++)
+		imx_dsp_request_channel(priv->dsp_ipc, i);
+
+	return 0;
+}
+
+static void imx8m_suspend(struct snd_sof_dev *sdev)
+{
+	struct imx8m_priv *priv = (struct imx8m_priv *)sdev->pdata->hw_pdata;
+	int i;
+
+	for (i = 0; i < DSP_MU_CHAN_NUM; i++)
+		imx_dsp_free_channel(priv->dsp_ipc, i);
+
+	imx8_disable_clocks(sdev, priv->clks);
+}
+
+static int imx8m_dsp_runtime_resume(struct snd_sof_dev *sdev)
+{
+	int ret;
+	const struct sof_dsp_power_state target_dsp_state = {
+		.state = SOF_DSP_PM_D0,
+	};
+
+	ret = imx8m_resume(sdev);
+	if (ret < 0)
+		return ret;
+
+	return snd_sof_dsp_set_power_state(sdev, &target_dsp_state);
+}
+
+static int imx8m_dsp_runtime_suspend(struct snd_sof_dev *sdev)
+{
+	const struct sof_dsp_power_state target_dsp_state = {
+		.state = SOF_DSP_PM_D3,
+	};
+
+	imx8m_suspend(sdev);
+
+	return snd_sof_dsp_set_power_state(sdev, &target_dsp_state);
+}
+
+static int imx8m_dsp_resume(struct snd_sof_dev *sdev)
+{
+	int ret;
+	const struct sof_dsp_power_state target_dsp_state = {
+		.state = SOF_DSP_PM_D0,
+	};
+
+	ret = imx8m_resume(sdev);
+	if (ret < 0)
+		return ret;
+
+	if (pm_runtime_suspended(sdev->dev)) {
+		pm_runtime_disable(sdev->dev);
+		pm_runtime_set_active(sdev->dev);
+		pm_runtime_mark_last_busy(sdev->dev);
+		pm_runtime_enable(sdev->dev);
+		pm_runtime_idle(sdev->dev);
+	}
+
+	return snd_sof_dsp_set_power_state(sdev, &target_dsp_state);
+}
+
+static int imx8m_dsp_suspend(struct snd_sof_dev *sdev, unsigned int target_state)
+{
+	const struct sof_dsp_power_state target_dsp_state = {
+		.state = target_state,
+	};
+
+	if (!pm_runtime_suspended(sdev->dev))
+		imx8m_suspend(sdev);
+
+	return snd_sof_dsp_set_power_state(sdev, &target_dsp_state);
+}
+
 /* i.MX8 ops */
 struct snd_sof_dsp_ops sof_imx8m_ops = {
 	/* probe and remove */
@@ -297,6 +393,14 @@ struct snd_sof_dsp_ops sof_imx8m_ops = {
 	.drv = imx8m_dai,
 	.num_drv = ARRAY_SIZE(imx8m_dai),
 
+	.suspend	= imx8m_dsp_suspend,
+	.resume		= imx8m_dsp_resume,
+
+	.runtime_suspend = imx8m_dsp_runtime_suspend,
+	.runtime_resume = imx8m_dsp_runtime_resume,
+
+	.set_power_state = imx8m_dsp_set_power_state,
+
 	.hw_info = SNDRV_PCM_INFO_MMAP |
 		SNDRV_PCM_INFO_MMAP_VALID |
 		SNDRV_PCM_INFO_INTERLEAVED |