ASoC: SOF: add a power_down_notify method

This patch adds a snd_sof_dsp_power_down_notify() method which aims to
prepare the DSP for the upcoming power down.
This new function make use of SOF_IPC_PM_CTX_SAVE message.
Signed-off-by: Marcin Rajwa <marcin.rajwa@linux.intel.com>
Signed-off-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>
Reviewed-by: Ranjani Sridharan <ranjani.sridharan@linux.intel.com>
Link: https://lore.kernel.org/r/20200515135958.17511-3-kai.vehmanen@linux.intel.comSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/sof/pm.c

@@ -256,6 +256,15 @@ static int sof_suspend(struct device *dev, bool runtime_suspend)
 	return ret;
 }
 
+int snd_sof_dsp_power_down_notify(struct snd_sof_dev *sdev)
+{
+	/* Notify DSP of upcoming power down */
+	if (sof_ops(sdev)->remove)
+		return sof_send_pm_ctx_ipc(sdev, SOF_IPC_PM_CTX_SAVE);
+
+	return 0;
+}
+
 int snd_sof_runtime_suspend(struct device *dev)
 {
 	return sof_suspend(dev, true);

sound/soc/sof/sof-priv.h

@@ -453,6 +453,7 @@ int snd_sof_runtime_resume(struct device *dev);
 int snd_sof_runtime_idle(struct device *dev);
 int snd_sof_resume(struct device *dev);
 int snd_sof_suspend(struct device *dev);
+int snd_sof_dsp_power_down_notify(struct snd_sof_dev *sdev);
 int snd_sof_prepare(struct device *dev);
 void snd_sof_complete(struct device *dev);