ALSA: emu10k1: fix PCM playback cache and interrupt handling

The cache causes a fixed delay regardless of stream parameters.
Consequently, all that "cache invalidate size" calculation stuff was
garbage (which can be traced right back to Creative's OSS driver).

This also removes the definitions of registers CD1..CDF, because they
are accessed only relative to CD0 anyway.

Signed-off-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>
Link: https://lore.kernel.org/r/20230517174256.3657060-5-oswald.buddenhagen@gmx.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>

1 files changed, 23 insertions, 44 deletions

diff --git a/sound/pci/emu10k1/emupcm.c b/sound/pci/emu10k1/emupcm.c
index a6c4f1895a08..feb575922738 100644
--- a/sound/pci/emu10k1/emupcm.c
+++ b/sound/pci/emu10k1/emupcm.c
@@ -112,6 +112,10 @@ static int snd_emu10k1_pcm_channel_alloc(struct snd_emu10k1_pcm * epcm, int voic
 		}
 	}
 	if (epcm->extra == NULL) {
+		// The hardware supports only (half-)loop interrupts, so to support an
+		// arbitrary number of periods per buffer, we use an extra voice with a
+		// period-sized loop as the interrupt source. Additionally, the interrupt
+		// timing of the hardware is "suboptimal" and needs some compensation.
 		err = snd_emu10k1_voice_alloc(epcm->emu,
 					      epcm->type == PLAYBACK_EMUVOICE ? EMU10K1_PCM : EMU10K1_EFX,
 					      1,
@@ -232,23 +236,6 @@ static unsigned int emu10k1_select_interprom(unsigned int pitch_target)
 		return CCCA_INTERPROM_2;
 }
 
-/*
- * calculate cache invalidate size 
- *
- * stereo: channel is stereo
- * w_16: using 16bit samples
- *
- * returns: cache invalidate size in samples
- */
-static inline int emu10k1_ccis(int stereo, int w_16)
-{
-	if (w_16) {
-		return stereo ? 24 : 26;
-	} else {
-		return stereo ? 24*2 : 26*2;
-	}
-}
-
 static void snd_emu10k1_pcm_init_voice(struct snd_emu10k1 *emu,
 				       int master, int extra,
 				       struct snd_emu10k1_voice *evoice,
@@ -264,7 +251,6 @@ static void snd_emu10k1_pcm_init_voice(struct snd_emu10k1 *emu,
 	unsigned char send_routing[8];
 	unsigned long flags;
 	unsigned int pitch_target;
-	unsigned int ccis;
 
 	voice = evoice->number;
 	stereo = runtime->channels == 2;
@@ -284,10 +270,8 @@ static void snd_emu10k1_pcm_init_voice(struct snd_emu10k1 *emu,
 		memcpy(send_amount, &mix->send_volume[tmp][0], 8);
 	}
 
-	ccis = emu10k1_ccis(stereo, w_16);
-	
 	if (master) {
-		evoice->epcm->ccca_start_addr = start_addr + ccis;
+		evoice->epcm->ccca_start_addr = start_addr + 64 - 3;
 	}
 	if (stereo && !extra) {
 		// Not really necessary for the slave, but it doesn't hurt
@@ -317,11 +301,11 @@ static void snd_emu10k1_pcm_init_voice(struct snd_emu10k1 *emu,
 	else 
 		pitch_target = emu10k1_calc_pitch_target(runtime->rate);
 	if (extra)
-		snd_emu10k1_ptr_write(emu, CCCA, voice, start_addr |
+		snd_emu10k1_ptr_write(emu, CCCA, voice, (end_addr - 3) |
 			      emu10k1_select_interprom(pitch_target) |
 			      (w_16 ? 0 : CCCA_8BITSELECT));
 	else
-		snd_emu10k1_ptr_write(emu, CCCA, voice, (start_addr + ccis) |
+		snd_emu10k1_ptr_write(emu, CCCA, voice, (start_addr + 64 - 3) |
 			      emu10k1_select_interprom(pitch_target) |
 			      (w_16 ? 0 : CCCA_8BITSELECT));
 	/* Clear filter delay memory */
@@ -532,35 +516,30 @@ static void snd_emu10k1_playback_invalidate_cache(struct snd_emu10k1 *emu,
 						  struct snd_emu10k1_voice *evoice)
 {
 	struct snd_pcm_runtime *runtime;
-	unsigned int voice, stereo, i, ccis, cra = 64, cs, sample;
+	unsigned voice, stereo, sample;
+	u32 ccr;
 
 	runtime = evoice->epcm->substream->runtime;
 	voice = evoice->number;
 	stereo = (runtime->channels == 2);
 	sample = snd_pcm_format_width(runtime->format) == 16 ? 0 : 0x80808080;
-	ccis = emu10k1_ccis(stereo, sample == 0);
-	/* set cs to 2 * number of cache registers beside the invalidated */
-	cs = (sample == 0) ? (32-ccis) : (64-ccis+1) >> 1;
-	if (cs > 16) cs = 16;
-	for (i = 0; i < cs; i++) {
+
+	// We assume that the cache is resting at this point (i.e.,
+	// CCR_CACHEINVALIDSIZE is very small).
+
+	// Clear leading frames. For simplicitly, this does too much,
+	// except for 16-bit stereo. And the interpolator will actually
+	// access them at all only when we're pitch-shifting.
+	for (int i = 0; i < 3; i++)
 		snd_emu10k1_ptr_write(emu, CD0 + i, voice, sample);
-		if (stereo) {
-			snd_emu10k1_ptr_write(emu, CD0 + i, voice + 1, sample);
-		}
-	}
-	/* reset cache */
-	snd_emu10k1_ptr_write(emu, CCR_CACHEINVALIDSIZE, voice, 0);
-	snd_emu10k1_ptr_write(emu, CCR_READADDRESS, voice, cra);
-	if (stereo) {
-		snd_emu10k1_ptr_write(emu, CCR_CACHEINVALIDSIZE, voice + 1, 0);
-		// The engine goes haywire if this one is out of sync
-		snd_emu10k1_ptr_write(emu, CCR_READADDRESS, voice + 1, cra);
-	}
-	/* fill cache */
-	snd_emu10k1_ptr_write(emu, CCR_CACHEINVALIDSIZE, voice, ccis);
+
+	// Fill cache
+	ccr = (64 - 3) << REG_SHIFT(CCR_CACHEINVALIDSIZE);
 	if (stereo) {
-		snd_emu10k1_ptr_write(emu, CCR_CACHEINVALIDSIZE, voice+1, ccis);
+		// The engine goes haywire if CCR_READADDRESS is out of sync
+		snd_emu10k1_ptr_write(emu, CCR, voice + 1, ccr);
 	}
+	snd_emu10k1_ptr_write(emu, CCR, voice, ccr);
 }
 
 static void snd_emu10k1_playback_commit_volume(struct snd_emu10k1 *emu,