From 49cdb468c28ba366dbd08eef9cb6dbf2dea2a2e5 Mon Sep 17 00:00:00 2001
From: Wim Taymans <wtaymans@redhat.com>
Date: Mon, 20 Nov 2023 13:14:54 +0100
Subject: [PATCH] alsa: also use interpolated time as nsec in IRQ mode

Don't use the current time as the nsec field in the graph clock because
it can jitter a lot. Instead, use the smoothed next_time, like we do
for timer based scheduling.

Since we track the current time against the rate converted ideal time,
lock on to the first timestamp when we reset the dll.

See #3657
---
 spa/plugins/alsa/alsa-pcm.c | 32 +++++++++++++++++++-------------
 1 file changed, 19 insertions(+), 13 deletions(-)

diff --git a/spa/plugins/alsa/alsa-pcm.c b/spa/plugins/alsa/alsa-pcm.c
index 229b9b0b6..2830b1aca 100644
--- a/spa/plugins/alsa/alsa-pcm.c
+++ b/spa/plugins/alsa/alsa-pcm.c
@@ -2531,6 +2531,15 @@ static int get_status(struct state *state, uint64_t current_time, snd_pcm_uframe
 	return 0;
 }
 
+
+static uint64_t get_time_ns(struct state *state)
+{
+	struct timespec now;
+	if (spa_system_clock_gettime(state->data_system, CLOCK_MONOTONIC, &now) < 0)
+		return 0;
+	return SPA_TIMESPEC_TO_NSEC(&now);
+}
+
 static int update_time(struct state *state, uint64_t current_time, snd_pcm_sframes_t delay,
 		snd_pcm_sframes_t target, bool follower)
 {
@@ -2538,8 +2547,15 @@ static int update_time(struct state *state, uint64_t current_time, snd_pcm_sfram
 	int32_t diff;
 
 	if (state->disable_tsched && !follower) {
-		err = (int64_t)(current_time - state->next_time);
-		err = err / 1e9 * state->rate;
+		uint64_t now = get_time_ns(state);
+
+		if (SPA_UNLIKELY(state->dll.bw == 0.0)) {
+			current_time = now;
+			err = 0.0;
+		} else {
+			err = (int64_t)(now - current_time);
+			err = err / 1e9 * state->rate;
+		}
 	} else {
 		if (state->stream == SND_PCM_STREAM_PLAYBACK)
 			err = delay - target;
@@ -3166,14 +3182,6 @@ static int capture_ready(struct state *state)
 	return 0;
 }
 
-static uint64_t get_time_ns(struct state *state)
-{
-	struct timespec now;
-	if (spa_system_clock_gettime(state->data_system, CLOCK_MONOTONIC, &now) < 0)
-		return 0;
-	return SPA_TIMESPEC_TO_NSEC(&now);
-}
-
 static void alsa_wakeup_event(struct spa_source *source)
 {
 	struct state *state = source->data, *follower;
@@ -3185,8 +3193,6 @@ static void alsa_wakeup_event(struct spa_source *source)
 		int err;
 		unsigned short revents;
 
-		current_time = get_time_ns(state);
-
 		for (int i = 0; i < state->n_fds; i++) {
 			state->pfds[i].revents = state->source[i].rmask;
 			/* Reset so that we only handle all our sources' events once */
@@ -3222,8 +3228,8 @@ static void alsa_wakeup_event(struct spa_source *source)
 				return;
 			}
 		}
-		current_time = state->next_time;
 	}
+	current_time = state->next_time;
 
 	/* first do all the sync */
 	if (state->stream == SND_PCM_STREAM_CAPTURE)