[PATCH] ASoC: codecs: wcd939x: read the SoundWire port switches per channel

[Joonhoe Kim <26rote@gmail.com>]

The "HPHL/HPHR", "ADCn" and "DMICn" switches are channels of shared
SoundWire ports (ADC1-4 are channels 0-3 of the ADC_1_4 port), but
wcd939x_get_swr_port() reports a per-port flag. Once one channel of a
port is switched on, every switch on that port reads back as on:

  amixer cset name='ADC1 Switch' on   -> ADC1..ADC4 Switch all read "on"

Setting one of the others then looks like a no-op to userspace, and
"alsactl store" saves all of them as on, so a later "alsactl restore"
really enables the unused channels of the port.

Read the channel's own bit in the port's channel mask instead, drop the
now unused port_enable[] and return 0 from the put handler when the
switch does not change, as ALSA expects.

Fixes: 10f514bd172a ("ASoC: codecs: Add WCD939x Codec driver")
Link: https://lore.kernel.org/all/20251124064850.15419-6-jonathan@marek.ca/
Assisted-by: LLM
Signed-off-by: Joonhoe Kim <26rote@gmail.com>
---
Jonathan Marek posted the same read-back change in November 2025 as
part of a wcd938x/wcd939x series [1]; the discussion stayed on the wsa
patches of that series and this one was not picked up. This version also
makes the put handler report "no change", which the original did not.
wcd938x and wcd937x keep the same per-port flag.

Tested on a Lenovo TB323FU (WCD9395, two-mic capture on ADC1/ADC3).
Before: with only ADC1 switched on, ADC1-4 all read back as on, and
after "alsactl store" and "alsactl restore" the TX port's ChannelEn was
0xf during capture. With this patch: ADC1-4 read on/off/on/off and
ChannelEn is 0x5. Writing the same value again no longer sends a change
event.

[1] https://lore.kernel.org/all/20251124064850.15419-1-jonathan@marek.ca/

 sound/soc/codecs/wcd939x.c | 10 +++++++---
 sound/soc/codecs/wcd939x.h |  1 -
 2 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/sound/soc/codecs/wcd939x.c b/sound/soc/codecs/wcd939x.c
index 26fe0b6313cd..2d463f062e6d 100644
--- a/sound/soc/codecs/wcd939x.c
+++ b/sound/soc/codecs/wcd939x.c
@@ -1794,8 +1794,9 @@ static int wcd939x_get_swr_port(struct snd_kcontrol *kcontrol,
 	struct wcd939x_priv *wcd939x = snd_soc_component_get_drvdata(comp);
 	struct wcd939x_sdw_priv *wcd = wcd939x->sdw_priv[mixer->shift];
 	unsigned int portidx = wcd->ch_info[mixer->reg].port_num;
+	u8 ch_mask = wcd->ch_info[mixer->reg].ch_mask;
 
-	ucontrol->value.integer.value[0] = wcd->port_enable[portidx] ? 1 : 0;
+	ucontrol->value.integer.value[0] = !!(wcd->port_config[portidx - 1].ch_mask & ch_mask);
 
 	return 0;
 }
@@ -1821,10 +1822,13 @@ static int wcd939x_set_swr_port(struct snd_kcontrol *kcontrol,
 	struct wcd939x_priv *wcd939x = snd_soc_component_get_drvdata(comp);
 	struct wcd939x_sdw_priv *wcd = wcd939x->sdw_priv[mixer->shift];
 	unsigned int portidx = wcd->ch_info[mixer->reg].port_num;
+	u8 ch_mask = wcd->ch_info[mixer->reg].ch_mask;
+	bool enable = !!ucontrol->value.integer.value[0];
 
-	wcd->port_enable[portidx] = !!ucontrol->value.integer.value[0];
+	if (enable == !!(wcd->port_config[portidx - 1].ch_mask & ch_mask))
+		return 0;
 
-	wcd939x_connect_port(wcd, portidx, mixer->reg, wcd->port_enable[portidx]);
+	wcd939x_connect_port(wcd, portidx, mixer->reg, enable);
 
 	return 1;
 }
diff --git a/sound/soc/codecs/wcd939x.h b/sound/soc/codecs/wcd939x.h
index 6bd2366587a8..dab7ef108b48 100644
--- a/sound/soc/codecs/wcd939x.h
+++ b/sound/soc/codecs/wcd939x.h
@@ -899,7 +899,6 @@ struct wcd939x_sdw_priv {
 	struct sdw_stream_runtime *sruntime;
 	struct sdw_port_config port_config[WCD939X_MAX_SWR_PORTS];
 	const struct wcd_sdw_ch_info *ch_info;
-	bool port_enable[WCD939X_MAX_SWR_CH_IDS];
 	int active_ports;
 	bool is_tx;
 	struct wcd939x_priv *wcd939x;
-- 
2.43.0