From 64aaf8a832c4615af165abeb3b2db85a33f10642 Mon Sep 17 00:00:00 2001
From: Pauli Virtanen <pav@iki.fi>
Date: Sat, 6 Sep 2025 16:06:53 +0300
Subject: [PATCH] alsa: set minimum period count before automatic period size

Some devices (FireWire) fail to produce audio if period count is < 3,
and also have small buffer size. When quantum is too large, we might
then get too few periods and broken sound.

Set minimum for the period count in ALSA, to determine the maximum
period size we can use. If smaller than what we were going to use, round
down to power-of-2.

See #4785
---
 spa/plugins/alsa/alsa-pcm.c | 41 +++++++++++++++++++++++++++----------
 1 file changed, 30 insertions(+), 11 deletions(-)

diff --git a/spa/plugins/alsa/alsa-pcm.c b/spa/plugins/alsa/alsa-pcm.c
index 2c785872e..299f752b6 100644
--- a/spa/plugins/alsa/alsa-pcm.c
+++ b/spa/plugins/alsa/alsa-pcm.c
@@ -2328,6 +2328,35 @@ int spa_alsa_set_format(struct state *state, struct spa_audio_info *fmt, uint32_
 		}
 	}
 
+	if (state->default_period_num != 0) {
+		/* period number given use that */
+		periods = state->default_period_num;
+	} else if (state->disable_tsched) {
+		/* IRQ mode, use 3 periods. This is a bit of a workaround
+		 * for Firewire devices, which seem to only work with 3 periods.
+		 * For PipeWire it does not actually matter how many periods
+		 * are used, we will always keep 1 filled, so we can work fine
+		 * with anything from 2 periods to MAX. */
+		periods = 3;
+	} else {
+		periods = UINT_MAX;
+	}
+
+	if (state->default_period_size == 0) {
+		/* Some devices (FireWire) don't produce audio if period number is too
+		 * small, so force a minimum. This will restrict possible period sizes if
+		 * the device has small buffer (like FireWire), so force it only if
+		 * period size was not set manually.
+		 */
+		snd_pcm_uframes_t period_size_max;
+		unsigned int periods_min = (periods == UINT_MAX) ? 3 : periods;
+
+		CHECK(snd_pcm_hw_params_set_periods_min(hndl, params, &periods_min, &dir), "set_periods_min");
+		CHECK(snd_pcm_hw_params_get_period_size_max(params, &period_size_max, &dir), "get_period_size_max");
+		if (period_size > period_size_max)
+			period_size = SPA_MIN(period_size, flp2(period_size_max));
+	}
+
 	CHECK(snd_pcm_hw_params_set_period_size_near(hndl, params, &period_size, &dir), "set_period_size_near");
 
 	if (period_size == 0) {
@@ -2337,17 +2366,7 @@ int spa_alsa_set_format(struct state *state, struct spa_audio_info *fmt, uint32_
 
 	state->period_frames = period_size;
 
-	if (state->default_period_num != 0 || state->disable_tsched) {
-		if (state->default_period_num != 0)
-			/* period number given use that */
-			periods = state->default_period_num;
-		else
-			/* IRQ mode, use 3 periods. This is a bit of a workaround
-			 * for Firewire devices, which seem to only work with 3 periods.
-			 * For PipeWire it does not actually matter how many periods
-			 * are used, we will always keep 1 filled, so we can work fine
-			 * with anything from 2 periods to MAX. */
-			periods = 3;
+	if (periods != UINT_MAX) {
 		CHECK(snd_pcm_hw_params_set_periods_near(hndl, params, &periods, &dir), "set_periods");
 		state->buffer_frames = period_size * periods;
 	} else {