ALSA: emu10k1: fix PCM playback buffer size constraints

The period_bytes_min parameter and the buffer_bytes minimum constraint
made no sense at all, as they didn't reflect any hardware limitation.
Instead, apply a frame-based period_size minimum constraint, which is
derived from the cache size (it would be actually possible to go below
that, but it would require special handling, and it would be practically
impossible to keep up with the IRQ rate anyway).

Sync up the constraints of the EFX playback with those of the regular
playback, as there is no reason for them to diverge.

N.b., the maximum buffer size is actually arbitrary - the hardware could
go waay beyond 128 KiB.
Signed-off-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>
Link: https://lore.kernel.org/r/20230518092224.3696958-9-oswald.buddenhagen@gmx.deSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/pci/emu10k1/emupcm.c

@@ -444,9 +444,8 @@ static const struct snd_pcm_hardware snd_emu10k1_efx_playback =
 	.rate_max =		48000,
 	.channels_min =		NUM_EFX_PLAYBACK,
 	.channels_max =		NUM_EFX_PLAYBACK,
-	.buffer_bytes_max =	(64*1024),
-	.period_bytes_min =	64,
-	.period_bytes_max =	(64*1024),
+	.buffer_bytes_max =	(128*1024),
+	.period_bytes_max =	(128*1024),
 	.periods_min =		2,
 	.periods_max =		2,
 	.fifo_size =		0,
@@ -877,7 +876,6 @@ static const struct snd_pcm_hardware snd_emu10k1_playback =
 	.channels_min =		1,
 	.channels_max =		2,
 	.buffer_bytes_max =	(128*1024),
-	.period_bytes_min =	64,
 	.period_bytes_max =	(128*1024),
 	.periods_min =		1,
 	.periods_max =		1024,
@@ -982,13 +980,29 @@ static int snd_emu10k1_efx_playback_close(struct snd_pcm_substream *substream)
 	return 0;
 }
 
+static int snd_emu10k1_playback_set_constraints(struct snd_pcm_runtime *runtime)
+{
+	int err;
+
+	// The buffer size must be a multiple of the period size, to avoid a
+	// mismatch between the extra voice and the regular voices.
+	err = snd_pcm_hw_constraint_integer(runtime, SNDRV_PCM_HW_PARAM_PERIODS);
+	if (err < 0)
+		return err;
+	// The hardware is typically the cache's size of 64 frames ahead.
+	// Leave enough time for actually filling up the buffer.
+	err = snd_pcm_hw_constraint_minmax(
+			runtime, SNDRV_PCM_HW_PARAM_PERIOD_SIZE, 128, UINT_MAX);
+	return err;
+}
+
 static int snd_emu10k1_efx_playback_open(struct snd_pcm_substream *substream)
 {
 	struct snd_emu10k1 *emu = snd_pcm_substream_chip(substream);
 	struct snd_emu10k1_pcm *epcm;
 	struct snd_emu10k1_pcm_mixer *mix;
 	struct snd_pcm_runtime *runtime = substream->runtime;
-	int i, j;
+	int i, j, err;
 
 	epcm = kzalloc(sizeof(*epcm), GFP_KERNEL);
 	if (epcm == NULL)
@@ -1000,7 +1014,12 @@ static int snd_emu10k1_efx_playback_open(struct snd_pcm_substream *substream)
 	runtime->private_data = epcm;
 	runtime->private_free = snd_emu10k1_pcm_free_substream;
 	runtime->hw = snd_emu10k1_efx_playback;
-	
+	err = snd_emu10k1_playback_set_constraints(runtime);
+	if (err < 0) {
+		kfree(epcm);
+		return err;
+	}
+
 	for (i = 0; i < NUM_EFX_PLAYBACK; i++) {
 		mix = &emu->efx_pcm_mixer[i];
 		for (j = 0; j < 8; j++)
@@ -1031,12 +1050,7 @@ static int snd_emu10k1_playback_open(struct snd_pcm_substream *substream)
 	runtime->private_data = epcm;
 	runtime->private_free = snd_emu10k1_pcm_free_substream;
 	runtime->hw = snd_emu10k1_playback;
-	err = snd_pcm_hw_constraint_integer(runtime, SNDRV_PCM_HW_PARAM_PERIODS);
-	if (err < 0) {
-		kfree(epcm);
-		return err;
-	}
-	err = snd_pcm_hw_constraint_minmax(runtime, SNDRV_PCM_HW_PARAM_BUFFER_BYTES, 256, UINT_MAX);
+	err = snd_emu10k1_playback_set_constraints(runtime);
 	if (err < 0) {
 		kfree(epcm);
 		return err;