[PATCH v2 1/2] ASoC: sdw_utils: prepare the stream again when resuming

A peripheral loses its Data Port configuration when the controller is
power-gated during system suspend, so the ports have to be prepared
again before the stream can be enabled.  That happens on its own when
userspace calls snd_pcm_prepare() after SNDRV_PCM_STATE_SUSPENDED, but
an application is also allowed to restart the stream with
SNDRV_PCM_IOCTL_RESUME on a card that advertises SNDRV_PCM_INFO_RESUME,
as the AMD ACP platforms do.  That path only reaches the trigger
callback, sdw_enable_stream() writes the channels of ports that were
never prepared, and playback silently produces nothing: the PCM keeps
running, no error is reported anywhere, and the speakers stay quiet
until the stream is torn down and set up again.

Prepare the stream on SNDRV_PCM_TRIGGER_RESUME, before enabling it.
The SoundWire core expects exactly this: sdw_prepare_stream() accepts a
disabled stream and then reapplies the bus parameters without
recomputing them, which it documents as the resume case.

Signed-off-by: Andrey Golovko <[email protected]>
---
New in v2, after Mark Brown and Vijendar Mukunda pointed out that a stream
restarted with SNDRV_PCM_IOCTL_RESUME never prepares its ports again.

Measured on an ASUS ProArt PX13 HN7306EAC: without this patch a tone that
is resumed with snd_pcm_resume() alone comes back inaudible with DP1
PrepareCtrl at 0x0 and PDE23 at PS3, with it the ports are prepared again
and the tone returns at its pre-suspend level.  Numbers are in the cover
letter.
 sound/soc/sdw_utils/soc_sdw_utils.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/sound/soc/sdw_utils/soc_sdw_utils.c b/sound/soc/sdw_utils/soc_sdw_utils.c
index 8a07ba2a29e5..3e091e78d8c2 100644
--- a/sound/soc/sdw_utils/soc_sdw_utils.c
+++ b/sound/soc/sdw_utils/soc_sdw_utils.c
@@ -1510,9 +1510,24 @@ int asoc_sdw_trigger(struct snd_pcm_substream *substream, int cmd)
 	}
 
 	switch (cmd) {
+	case SNDRV_PCM_TRIGGER_RESUME:
+		/*
+		 * The peripherals lose their port configuration when the
+		 * controller is power-gated during system suspend, and an
+		 * application that restarts the stream with
+		 * SNDRV_PCM_IOCTL_RESUME - which platforms advertising
+		 * SNDRV_PCM_INFO_RESUME allow - never goes through
+		 * .prepare() again.  Prepare the stream here so that the
+		 * ports are reprogrammed before they are enabled;
+		 * sdw_prepare_stream() reapplies the parameters without
+		 * recomputing them when the stream is disabled.
+		 */
+		ret = sdw_prepare_stream(sdw_stream);
+		if (ret)
+			break;
+		fallthrough;
 	case SNDRV_PCM_TRIGGER_START:
 	case SNDRV_PCM_TRIGGER_PAUSE_RELEASE:
-	case SNDRV_PCM_TRIGGER_RESUME:
 		ret = sdw_enable_stream(sdw_stream);
 		break;
 
-- 
2.53.0