ALSA: emu10k1: add synchronized start of multi-channel playback

We use independent voices for the channels, so we need to make an effort
to ensure that they are actually in sync.

The hardware doesn't provide atomicity, so we may need to retry a few
times, due to NMIs, PCI contention, and the wrong phase of the moon.

Solution inspired by kX-project.

Signed-off-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>
Link: https://lore.kernel.org/r/20230523200709.236023-3-oswald.buddenhagen@gmx.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>

2 files changed, 164 insertions, 18 deletions

diff --git a/sound/pci/emu10k1/emupcm.c b/sound/pci/emu10k1/emupcm.c
index 2764e7867b33..4df6f5285993 100644
--- a/sound/pci/emu10k1/emupcm.c
+++ b/sound/pci/emu10k1/emupcm.c
@@ -560,7 +560,7 @@ static void snd_emu10k1_playback_prepare_voices(struct snd_emu10k1 *emu,
 	// we need to compensate for two circumstances:
 	// - The actual position is delayed by the cache size (64 frames)
 	// - The interpolator is centered around the 4th frame
-	loop_start += 64 - 3;
+	loop_start += (epcm->resume_pos + 64 - 3) % loop_size;
 	for (int i = 0; i < channels; i++) {
 		unsigned voice = epcm->voices[i]->number;
 		snd_emu10k1_ptr_write(emu, CCCA_CURRADDR, voice, loop_start);
@@ -584,7 +584,7 @@ static void snd_emu10k1_playback_prepare_voices(struct snd_emu10k1 *emu,
 	// This is why all other (open) drivers for these chips use timer-based
 	// interrupts.
 	//
-	eloop_start += eloop_size - 3;
+	eloop_start += (epcm->resume_pos + eloop_size - 3) % eloop_size;
 	snd_emu10k1_ptr_write(emu, CCCA_CURRADDR, epcm->extra->number, eloop_start);
 
 	// It takes a moment until the cache fills complete,
@@ -844,6 +844,49 @@ static snd_pcm_uframes_t snd_emu10k1_playback_pointer(struct snd_pcm_substream *
 	return ptr;
 }
 
+static u64 snd_emu10k1_efx_playback_voice_mask(struct snd_emu10k1_pcm *epcm,
+					       int channels)
+{
+	u64 mask = 0;
+
+	for (int i = 0; i < channels; i++) {
+		int voice = epcm->voices[i]->number;
+		mask |= 1ULL << voice;
+	}
+	return mask;
+}
+
+static void snd_emu10k1_efx_playback_freeze_voices(struct snd_emu10k1 *emu,
+						   struct snd_emu10k1_pcm *epcm,
+						   int channels)
+{
+	for (int i = 0; i < channels; i++) {
+		int voice = epcm->voices[i]->number;
+		snd_emu10k1_ptr_write(emu, CPF_STOP, voice, 1);
+		snd_emu10k1_playback_commit_pitch(emu, voice, PITCH_48000 << 16);
+	}
+}
+
+static void snd_emu10k1_efx_playback_unmute_voices(struct snd_emu10k1 *emu,
+						   struct snd_emu10k1_pcm *epcm,
+						   int channels)
+{
+	for (int i = 0; i < channels; i++)
+		snd_emu10k1_playback_unmute_voice(emu, epcm->voices[i], false, true,
+						  &emu->efx_pcm_mixer[i]);
+}
+
+static void snd_emu10k1_efx_playback_stop_voices(struct snd_emu10k1 *emu,
+						 struct snd_emu10k1_pcm *epcm,
+						 int channels)
+{
+	for (int i = 0; i < channels; i++)
+		snd_emu10k1_playback_stop_voice(emu, epcm->voices[i]);
+	snd_emu10k1_playback_set_stopped(emu, epcm);
+
+	for (int i = 0; i < channels; i++)
+		snd_emu10k1_playback_mute_voice(emu, epcm->voices[i]);
+}
 
 static int snd_emu10k1_efx_playback_trigger(struct snd_pcm_substream *substream,
 				        int cmd)
@@ -851,41 +894,62 @@ static int snd_emu10k1_efx_playback_trigger(struct snd_pcm_substream *substream,
 	struct snd_emu10k1 *emu = snd_pcm_substream_chip(substream);
 	struct snd_pcm_runtime *runtime = substream->runtime;
 	struct snd_emu10k1_pcm *epcm = runtime->private_data;
-	int i;
+	u64 mask;
 	int result = 0;
 
 	spin_lock(&emu->reg_lock);
 	switch (cmd) {
 	case SNDRV_PCM_TRIGGER_START:
-		snd_emu10k1_playback_prepare_voices(emu, epcm, true, false, NUM_EFX_PLAYBACK);
-		fallthrough;
 	case SNDRV_PCM_TRIGGER_PAUSE_RELEASE:
 	case SNDRV_PCM_TRIGGER_RESUME:
-		for (i = 0; i < NUM_EFX_PLAYBACK; i++)
-			snd_emu10k1_playback_unmute_voice(emu, epcm->voices[i], false, true,
-							  &emu->efx_pcm_mixer[i]);
+		mask = snd_emu10k1_efx_playback_voice_mask(
+				epcm, NUM_EFX_PLAYBACK);
+		for (int i = 0; i < 10; i++) {
+			// Note that the freeze is not interruptible, so we make no
+			// effort to reset the bits outside the error handling here.
+			snd_emu10k1_voice_set_loop_stop_multiple(emu, mask);
+			snd_emu10k1_efx_playback_freeze_voices(
+					emu, epcm, NUM_EFX_PLAYBACK);
+			snd_emu10k1_playback_prepare_voices(
+					emu, epcm, true, false, NUM_EFX_PLAYBACK);
+
+			// It might seem to make more sense to unmute the voices only after
+			// they have been started, to potentially avoid torturing the speakers
+			// if something goes wrong. However, we cannot unmute atomically,
+			// which means that we'd get some mild artifacts in the regular case.
+			snd_emu10k1_efx_playback_unmute_voices(emu, epcm, NUM_EFX_PLAYBACK);
+
+			snd_emu10k1_playback_set_running(emu, epcm);
+			result = snd_emu10k1_voice_clear_loop_stop_multiple_atomic(emu, mask);
+			if (result == 0) {
+				// The extra voice is allowed to lag a bit
+				snd_emu10k1_playback_trigger_voice(emu, epcm->extra);
+				goto leave;
+			}
 
-		snd_emu10k1_playback_set_running(emu, epcm);
-		for (i = 0; i < NUM_EFX_PLAYBACK; i++)
-			snd_emu10k1_playback_trigger_voice(emu, epcm->voices[i]);
-		snd_emu10k1_playback_trigger_voice(emu, epcm->extra);
+			snd_emu10k1_efx_playback_stop_voices(
+					emu, epcm, NUM_EFX_PLAYBACK);
+
+			if (result != -EAGAIN)
+				break;
+			// The sync start can legitimately fail due to NMIs, etc.
+		}
+		snd_emu10k1_voice_clear_loop_stop_multiple(emu, mask);
 		break;
 	case SNDRV_PCM_TRIGGER_SUSPEND:
 	case SNDRV_PCM_TRIGGER_STOP:
 	case SNDRV_PCM_TRIGGER_PAUSE_PUSH:
-		for (i = 0; i < NUM_EFX_PLAYBACK; i++) {	
-			snd_emu10k1_playback_stop_voice(emu, epcm->voices[i]);
-		}
 		snd_emu10k1_playback_stop_voice(emu, epcm->extra);
-		snd_emu10k1_playback_set_stopped(emu, epcm);
+		snd_emu10k1_efx_playback_stop_voices(
+				emu, epcm, NUM_EFX_PLAYBACK);
 
-		for (i = 0; i < NUM_EFX_PLAYBACK; i++)
-			snd_emu10k1_playback_mute_voice(emu, epcm->voices[i]);
+		epcm->resume_pos = snd_emu10k1_playback_pointer(substream);
 		break;
 	default:
 		result = -EINVAL;
 		break;
 	}
+leave:
 	spin_unlock(&emu->reg_lock);
 	return result;
 }
diff --git a/sound/pci/emu10k1/io.c b/sound/pci/emu10k1/io.c
index 6419719c739c..9a839e7d283f 100644
--- a/sound/pci/emu10k1/io.c
+++ b/sound/pci/emu10k1/io.c
@@ -505,6 +505,88 @@ void snd_emu10k1_voice_clear_loop_stop(struct snd_emu10k1 *emu, unsigned int voi
 }
 #endif
 
+void snd_emu10k1_voice_set_loop_stop_multiple(struct snd_emu10k1 *emu, u64 voices)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&emu->emu_lock, flags);
+	outl(SOLEL << 16, emu->port + PTR);
+	outl(inl(emu->port + DATA) | (u32)voices, emu->port + DATA);
+	outl(SOLEH << 16, emu->port + PTR);
+	outl(inl(emu->port + DATA) | (u32)(voices >> 32), emu->port + DATA);
+	spin_unlock_irqrestore(&emu->emu_lock, flags);
+}
+
+void snd_emu10k1_voice_clear_loop_stop_multiple(struct snd_emu10k1 *emu, u64 voices)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&emu->emu_lock, flags);
+	outl(SOLEL << 16, emu->port + PTR);
+	outl(inl(emu->port + DATA) & (u32)~voices, emu->port + DATA);
+	outl(SOLEH << 16, emu->port + PTR);
+	outl(inl(emu->port + DATA) & (u32)(~voices >> 32), emu->port + DATA);
+	spin_unlock_irqrestore(&emu->emu_lock, flags);
+}
+
+int snd_emu10k1_voice_clear_loop_stop_multiple_atomic(struct snd_emu10k1 *emu, u64 voices)
+{
+	unsigned long flags;
+	u32 soll, solh;
+	int ret = -EIO;
+
+	spin_lock_irqsave(&emu->emu_lock, flags);
+
+	outl(SOLEL << 16, emu->port + PTR);
+	soll = inl(emu->port + DATA);
+	outl(SOLEH << 16, emu->port + PTR);
+	solh = inl(emu->port + DATA);
+
+	soll &= (u32)~voices;
+	solh &= (u32)(~voices >> 32);
+
+	for (int tries = 0; tries < 1000; tries++) {
+		const u32 quart = 1U << (REG_SIZE(WC_CURRENTCHANNEL) - 2);
+		// First we wait for the third quarter of the sample cycle ...
+		u32 wc = inl(emu->port + WC);
+		u32 cc = REG_VAL_GET(WC_CURRENTCHANNEL, wc);
+		if (cc >= quart * 2 && cc < quart * 3) {
+			// ... and release the low voices, while the high ones are serviced.
+			outl(SOLEL << 16, emu->port + PTR);
+			outl(soll, emu->port + DATA);
+			// Then we wait for the first quarter of the next sample cycle ...
+			for (; tries < 1000; tries++) {
+				cc = REG_VAL_GET(WC_CURRENTCHANNEL, inl(emu->port + WC));
+				if (cc < quart)
+					goto good;
+				// We will block for 10+ us with interrupts disabled. This is
+				// not nice at all, but necessary for reasonable reliability.
+				udelay(1);
+			}
+			break;
+		good:
+			// ... and release the high voices, while the low ones are serviced.
+			outl(SOLEH << 16, emu->port + PTR);
+			outl(solh, emu->port + DATA);
+			// Finally we verify that nothing interfered in fact.
+			if (REG_VAL_GET(WC_SAMPLECOUNTER, inl(emu->port + WC)) ==
+			    ((REG_VAL_GET(WC_SAMPLECOUNTER, wc) + 1) & REG_MASK0(WC_SAMPLECOUNTER))) {
+				ret = 0;
+			} else {
+				ret = -EAGAIN;
+			}
+			break;
+		}
+		// Don't block for too long
+		spin_unlock_irqrestore(&emu->emu_lock, flags);
+		udelay(1);
+		spin_lock_irqsave(&emu->emu_lock, flags);
+	}
+
+	spin_unlock_irqrestore(&emu->emu_lock, flags);
+	return ret;
+}
+
 void snd_emu10k1_wait(struct snd_emu10k1 *emu, unsigned int wait)
 {
 	volatile unsigned count;