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

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

[Roman Prucha via B4 Relay]

From: Roman Prucha <zorgan.roman@gmail.com>

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 <zorgan.roman@gmail.com>
---
 sound/pci/ctxfi/cthw20k2.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/sound/pci/ctxfi/cthw20k2.c b/sound/pci/ctxfi/cthw20k2.c
index 07e1490a6d17..36066ffe8784 100644
--- a/sound/pci/ctxfi/cthw20k2.c
+++ b/sound/pci/ctxfi/cthw20k2.c
@@ -994,6 +994,7 @@ static int daio_mgr_dao_init(struct hw *hw, void *blk, unsigned int idx, unsigne
 		/* S/PDIF output */
 		switch ((conf & 0xf)) {
 		case 1:
+		case 9:
 			set_field(&ctl->txctl[idx], ATXCTL_NUC, 0);
 			break;
 		case 2:

---
base-commit: 7f71fd44a1089b362eacf87e1f451ddd4fb7df62
change-id: 20260903-ctxfi-spdif-conf9-fix-b909f7e366dc

Best regards,
-- 
Roman Prucha <zorgan.roman@gmail.com>

Re: [PATCH] ALSA: ctxfi: Fix CA20K2 S/PDIF passthrough

[Takashi Iwai]

On Thu, 03 Sep 2026 23:14:44 +0200,
Roman Prucha via B4 Relay wrote:
> 
> From: Roman Prucha <zorgan.roman@gmail.com>
> 
> 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 <zorgan.roman@gmail.com>

Applied now.  Thanks.


Takashi