[PATCH 6.12 0810/1102] ALSA: ctxfi: Fix CA20K2 S/PDIF passthrough

6.12-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Roman Prucha <redacted>

commit b26a7a80e6bbf8dd17dacb127d12435d79375cf2 upstream.

dao_rsc_init() encodes the DAIO configuration as

    conf = (desc->msr & 0x7) | (desc->passthru << 3);

S/PDIF passthrough uses msr=1 and passthru=1, resulting in
conf=9.

daio_mgr_dao_init() masks conf with 0xf, but handles only values
1, 2, 4 and 8 when programming ATXCTL_NUC. As a result, conf=9
falls through to the default case and leaves NUC at its previous
setting.

On a Creative X-Fi Titanium HD SB1270 (CA20K2), this breaks AC3
IEC61937 passthrough when snd_ctxfi runs with
reference_rate=48000,multiple=2. The receiver detects a non-audio
stream but cannot decode the AC3 payload.

With the unmodified driver, multiple=1 makes the same stream work.
Handle conf=9 through the same NUC=0 path as conf=1.

The change was runtime tested on the SB1270 with multiple=2 using
IEC958 stereo PCM, pre-encoded AC3 IEC61937 passthrough and ALSA
A52 live 5.1 encoding.

Fixes: 26a9630c72eb ("ALSA: ctxfi: cthw20k2: fix mask on conf to allow 4 bits")
Cc: stable@vger.kernel.org
Assisted-by: LLM
Signed-off-by: Roman Prucha <redacted>
Link: https://patch.msgid.link/20260903-ctxfi-spdif-conf9-fix-v1-1-5e4e3e1f801c@gmail.com (local)
Signed-off-by: Takashi Iwai <redacted>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 sound/pci/ctxfi/cthw20k2.c |    1 +
 1 file changed, 1 insertion(+)

--- a/sound/pci/ctxfi/cthw20k2.c
+++ b/sound/pci/ctxfi/cthw20k2.c

@@ -993,6 +993,7 @@ static int daio_mgr_dao_init(void *blk,
 		/* S/PDIF output */
 		switch ((conf & 0xf)) {
 		case 1:
+		case 9:
 			set_field(&ctl->txctl[idx], ATXCTL_NUC, 0);
 			break;
 		case 2: