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>

1 files changed, 82 insertions, 0 deletions

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;