From 1e98d531f2eef6a331512e89629518c57a832c30 Mon Sep 17 00:00:00 2001
From: RichardG867 <richardg867@gmail.com>
Date: Sat, 20 Nov 2021 22:59:08 -0300
Subject: [PATCH] Fix hijacking of the CD audio filter by VIA AC97

---
 src/chipset/via_pipc.c   |  3 +++
 src/sound/snd_ac97_via.c | 15 ++++++++++-----
 src/sound/snd_cs423x.c   |  4 ++--
 src/sound/snd_sb.c       |  1 -
 4 files changed, 15 insertions(+), 8 deletions(-)

diff --git a/src/chipset/via_pipc.c b/src/chipset/via_pipc.c
index 3829e337c..a2f3dc774 100644
--- a/src/chipset/via_pipc.c
+++ b/src/chipset/via_pipc.c
@@ -824,6 +824,9 @@ pipc_sb_handlers(pipc_t *dev, uint8_t modem)
 	sb_dsp_setirq(&dev->sb->dsp, (irq == 11) ? 10 : irq);
 
 	sb_dsp_setdma8(&dev->sb->dsp, (dev->ac97_regs[0][0x43] >> 4) & 0x03);
+
+	/* Set up CD audio filter. This might not actually work if VIAUDIO writes to CD volume through AC97. */
+	sound_set_cd_audio_filter(sbpro_filter_cd_audio, dev->sb);
     }
 
     if (dev->ac97_regs[0][0x42] & 0x02) {
diff --git a/src/sound/snd_ac97_via.c b/src/sound/snd_ac97_via.c
index de12edf75..aea9d6ee0 100644
--- a/src/sound/snd_ac97_via.c
+++ b/src/sound/snd_ac97_via.c
@@ -87,6 +87,7 @@ ac97_via_log(const char *fmt, ...)
 static void	ac97_via_sgd_process(void *priv);
 static void	ac97_via_update_codec(ac97_via_t *dev);
 static void	ac97_via_speed_changed(void *priv);
+static void	ac97_via_filter_cd_audio(int channel, double *buffer, void *priv);
 
 
 void
@@ -390,8 +391,15 @@ ac97_via_sgd_write(uint16_t addr, uint8_t val, void *priv)
 						*((uint16_t *) &dev->codec_shadow[modem].regs_codec[i][val & 0x7f]) = *((uint16_t *) &dev->sgd_regs[0x80]));
 
 					/* Update primary audio codec state if that codec was written to. */
-					if (!modem && !i)
+					if (!modem && !i) {
 						ac97_via_update_codec(dev);
+
+						/* Set up CD audio filter if CD volume was written to. Setting it
+						   up at init prevents CD audio from working on other cards, but
+						   this works as the CD channel is muted by default per AC97 spec. */
+						if (val == 0x12)
+							sound_set_cd_audio_filter(ac97_via_filter_cd_audio, dev);
+					}
 				}
 			}
 
@@ -741,7 +749,7 @@ ac97_via_get_buffer(int32_t *buffer, int len, void *priv)
 
 
 static void
-via_ac97_filter_cd_audio(int channel, double *buffer, void *priv)
+ac97_via_filter_cd_audio(int channel, double *buffer, void *priv)
 {
     ac97_via_t *dev = (ac97_via_t *) priv;
     double c, volume = channel ? dev->cd_vol_r : dev->cd_vol_l;
@@ -806,9 +814,6 @@ ac97_via_init(const device_t *info)
     /* Set up playback handler. */
     sound_add_handler(ac97_via_get_buffer, dev);
 
-    /* Set up CD audio filter. */
-    sound_set_cd_audio_filter(via_ac97_filter_cd_audio, dev);
-
     return dev;
 }
 
diff --git a/src/sound/snd_cs423x.c b/src/sound/snd_cs423x.c
index f3d95828d..c5b349c9e 100644
--- a/src/sound/snd_cs423x.c
+++ b/src/sound/snd_cs423x.c
@@ -779,9 +779,9 @@ cs423x_init(const device_t *info)
     /* Initialize ISAPnP. */
     dev->pnp_card = isapnp_add_card(NULL, 0, cs423x_pnp_config_changed, NULL, NULL, NULL, dev);
 
-    /* Initialize SBPro codec first to get the correct CD audio filter for the default
-       context, which is SBPro. The WSS codec is initialized later by cs423x_reset */
+    /* Initialize SBPro codec. The WSS codec is initialized later by cs423x_reset */
     dev->sb = device_add(&sb_pro_compat_device);
+    sound_set_cd_audio_filter(sbpro_filter_cd_audio, dev->sb); /* CD audio filter for the default context */
 
     /* Initialize RAM, registers and WSS codec. */
     cs423x_reset(dev);
diff --git a/src/sound/snd_sb.c b/src/sound/snd_sb.c
index f52e78c6c..ef0fa626d 100644
--- a/src/sound/snd_sb.c
+++ b/src/sound/snd_sb.c
@@ -1615,7 +1615,6 @@ sb_pro_compat_init(const device_t *info)
  
     sb->mixer_enabled = 1;
     sound_add_handler(sb_get_buffer_sbpro, sb);
-    sound_set_cd_audio_filter(sbpro_filter_cd_audio, sb);
 
     sb->mpu = (mpu_t *) malloc(sizeof(mpu_t));
     memset(sb->mpu, 0, sizeof(mpu_t));