[RFC] dpcm_fe_dai_do_trigger: implicit removal of _DRAIN cmd since v5.4

[Cezary Rojewski <cezary.rojewski@intel.com>]

Hello,

Till v5.4 dpcm_fe_dai_do_trigger was supporting all pcm cmds as each 
case: SND_SOC_DPCM_TRIGGER_PRE/ _POST/ _BESPOKE was simply passing cmd's 
value to appropriate variant of _trigger().

Since the addition of:
	acbf27746ecfa96b290b54cc7f05273482ea128a
	ASoC: pcm: update FE/BE trigger order based on the command

additional filters have been introduced for _PRE and _POST cases:

	switch (cmd) {
	case SNDRV_PCM_TRIGGER_START:
	case SNDRV_PCM_TRIGGER_RESUME:
	case SNDRV_PCM_TRIGGER_PAUSE_RELEASE:
		ret = dpcm_dai_trigger_fe_be(substream, cmd, true);
		break;
	case SNDRV_PCM_TRIGGER_STOP:
	case SNDRV_PCM_TRIGGER_SUSPEND:
	case SNDRV_PCM_TRIGGER_PAUSE_PUSH:
		ret = dpcm_dai_trigger_fe_be(substream, cmd, false);
		break;
	default:
		ret = -EINVAL;
		break;
	}

effectively removing support for _DRAIN command - all requests will 
yield -EINVAL. _BESPOKE was left alone so support remained there.

Now, is DPCM no longer supporting _DRAIN and that's how things should be 
-or- DPCM still intends to support _DRAIN and mentioned change is 
unintended regression?

Czarek