[PATCH v2 2/2] ASoC: tas2783-sdw: power the Function up before preparing the port

A Data Port cannot complete channel preparation while the SDCA Function
is powered down: the peripheral raises the channel's bit in
DPn_PrepareStatus and never clears it.

tas_sdw_hw_params() takes care of that for a stream that is being set
up, and the retry loop there says so - "ensure power on so that port
prepare succeeds".  Port preparation, however, also happens on a stream
that is merely re-prepared, without hw_params() running again.  That is
what userspace does after a suspend in which the peripheral lost power:
snd_pcm_prepare() reaches .prepare and sdw_prepare_stream(), the port is
prepared afresh, but PDE23 is still at the PS3 reset default because
nothing wrote it since the device came back.

The result is silence with no error anywhere.  The codec sets
simple_ch_prep_sm, so sdw_prep_deprep_slave_port() skips the
NOT_PREPARED poll, and a port that never prepares is indistinguishable
from a healthy one.

Power the Function up in the PRE_PREP callback, immediately before the
PrepareCtrl write it already performs, so that preparation has what it
needs on every path that prepares a port.

Measured on an ASUS ProArt PX13 (AMD ACP7.0, two TAS2783): after s2idle
with ~100 s of S0i3 residency, DPn_PrepareStatus stays at the channel
mask and there is no audio; writing PDE23 PS0 and re-issuing the prepare
clears it within 1 ms and audio returns.

Signed-off-by: Andrey Golovko <[email protected]>
---
v2: no functional change.  The comment no longer implies that a userspace
snd_pcm_prepare() is the only way into port preparation, since patch 1
now also reaches it from the resume trigger.
 sound/soc/codecs/tas2783-sdw.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/sound/soc/codecs/tas2783-sdw.c b/sound/soc/codecs/tas2783-sdw.c
index c217da5fccdf..d32d8f441651 100644
--- a/sound/soc/codecs/tas2783-sdw.c
+++ b/sound/soc/codecs/tas2783-sdw.c
@@ -1259,6 +1259,7 @@ static int tas_port_prep(struct sdw_slave *slave, struct sdw_prepare_ch *prep_ch
 			 enum sdw_port_prep_ops pre_ops)
 {
 	struct device *dev = &slave->dev;
+	struct tas2783_prv *tas_dev = dev_get_drvdata(dev);
 	struct sdw_dpn_prop *dpn_prop;
 	u32 addr;
 	int ret;
@@ -1270,6 +1271,25 @@ static int tas_port_prep(struct sdw_slave *slave, struct sdw_prepare_ch *prep_ch
 	addr = SDW_DPN_PREPARECTRL(prep_ch->num);
 	switch (pre_ops) {
 	case SDW_OPS_PORT_PRE_PREP:
+		/*
+		 * The Function has to be powered before the port can complete
+		 * channel preparation.  hw_params() does that when a stream is
+		 * set up, but a stream that is only re-prepared - as it is
+		 * after the peripheral lost power in S0i3 - does not go
+		 * through hw_params() again, and the peripheral is back at its
+		 * PS3 reset default.  Power it up here, where it is needed.
+		 */
+		scoped_guard(mutex, &tas_dev->pde_lock)
+			ret = regmap_write(tas_dev->regmap,
+					   SDW_SDCA_CTL(1, TAS2783_SDCA_ENT_PDE23,
+							TAS2783_SDCA_CTL_REQ_POW_STATE, 0),
+					   TAS2783_SDCA_POW_STATE_ON);
+		if (ret) {
+			dev_err(dev, "power up failed for port %d, err=%d\n",
+				prep_ch->num, ret);
+			return ret;
+		}
+
 		ret = sdw_write_no_pm(slave, addr, prep_ch->ch_mask);
 		if (ret)
 			dev_err(dev, "prep failed for port %d, err=%d\n",
-- 
2.53.0