[PATCH] DO-NOT-MERGE: pipewire sample code

[Volker Rümelin]

Based-on: <20230306171020.381116-1-dbassey@redhat.com>
([PATCH v7] audio/pwaudio.c: Add Pipewire audio backend for QEMU)

This is sample code for the review of the pipewire backed. The
code actually works.

An email with explanations for the changes will follow.

Signed-off-by: Volker Rümelin <vr_qemu@t-online.de>
---
 audio/pwaudio.c | 67 +++++++++++++++++++++++++++++++++----------------
 qapi/audio.json | 10 +++-----
 2 files changed, 49 insertions(+), 28 deletions(-)

diff --git a/audio/pwaudio.c b/audio/pwaudio.c
index d357761152..8e2a38938f 100644
--- a/audio/pwaudio.c
+++ b/audio/pwaudio.c
@@ -23,7 +23,6 @@
 #define AUDIO_CAP "pipewire"
 #define RINGBUFFER_SIZE    (1u << 22)
 #define RINGBUFFER_MASK    (RINGBUFFER_SIZE - 1)
-#define BUFFER_SAMPLES    512
 
 #include "audio_int.h"
 
@@ -48,6 +47,7 @@ typedef struct PWVoice {
     struct pw_stream *stream;
     struct spa_hook stream_listener;
     struct spa_audio_info_raw info;
+    uint32_t highwater_mark;
     uint32_t frame_size;
     struct spa_ringbuffer ring;
     uint8_t buffer[RINGBUFFER_SIZE];
@@ -82,7 +82,7 @@ playback_on_process(void *data)
     void *p;
     struct pw_buffer *b;
     struct spa_buffer *buf;
-    uint32_t n_frames, req, index, n_bytes;
+    uint32_t req, index, n_bytes;
     int32_t avail;
 
     if (!v->stream) {
@@ -105,8 +105,7 @@ playback_on_process(void *data)
     if (req == 0) {
         req = 4096 * v->frame_size;
     }
-    n_frames = SPA_MIN(req, buf->datas[0].maxsize);
-    n_bytes = n_frames * v->frame_size;
+    n_bytes = SPA_MIN(req, buf->datas[0].maxsize);
 
     /* get no of available bytes to read data from buffer */
 
@@ -270,6 +269,30 @@ done_unlock:
     return l;
 }
 
+static size_t qpw_buffer_get_free(HWVoiceOut *hw)
+{
+    PWVoiceOut *pw = (PWVoiceOut *)hw;
+    PWVoice *v = &pw->v;
+    pwaudio *c = v->g;
+    const char *error = NULL;
+    int32_t filled, avail;
+    uint32_t index;
+
+    pw_thread_loop_lock(c->thread_loop);
+    if (pw_stream_get_state(v->stream, &error) != PW_STREAM_STATE_STREAMING) {
+        /* wait for stream to become ready */
+        avail = 0;
+        goto done_unlock;
+    }
+
+    filled = spa_ringbuffer_get_write_index(&v->ring, &index);
+    avail = v->highwater_mark - filled;
+
+done_unlock:
+    pw_thread_loop_unlock(c->thread_loop);
+    return avail;
+}
+
 static size_t
 qpw_write(HWVoiceOut *hw, void *data, size_t len)
 {
@@ -277,20 +300,18 @@ qpw_write(HWVoiceOut *hw, void *data, size_t len)
     PWVoice *v = &pw->v;
     pwaudio *c = v->g;
     const char *error = NULL;
-    const int periods = 3;
-    size_t l;
     int32_t filled, avail;
     uint32_t index;
 
     pw_thread_loop_lock(c->thread_loop);
     if (pw_stream_get_state(v->stream, &error) != PW_STREAM_STATE_STREAMING) {
         /* wait for stream to become ready */
-        l = 0;
+        len = 0;
         goto done_unlock;
     }
-    filled = spa_ringbuffer_get_write_index(&v->ring, &index);
 
-    avail = BUFFER_SAMPLES * v->frame_size * periods - filled;
+    filled = spa_ringbuffer_get_write_index(&v->ring, &index);
+    avail = v->highwater_mark - filled;
 
     trace_pw_write(filled, avail, index, len);
 
@@ -312,11 +333,10 @@ qpw_write(HWVoiceOut *hw, void *data, size_t len)
                                 index & RINGBUFFER_MASK, data, len);
     index += len;
     spa_ringbuffer_write_update(&v->ring, index);
-    l = len;
 
 done_unlock:
     pw_thread_loop_unlock(c->thread_loop);
-    return l;
+    return len;
 }
 
 static int
@@ -420,8 +440,13 @@ create_stream(pwaudio *c, PWVoice *v, const char *name)
     const struct spa_pod *params[2];
     uint8_t buffer[1024];
     struct spa_pod_builder b;
+    struct pw_properties *props;
 
-    v->stream = pw_stream_new(c->core, name, NULL);
+    props = pw_properties_new(NULL, NULL);
+    pw_properties_setf(props, PW_KEY_NODE_LATENCY, "%" PRIu64 "/%u",
+                       (uint64_t)v->g->dev->timer_period * v->info.rate
+                       * 3 / 4 / 1000000, v->info.rate);
+    v->stream = pw_stream_new(c->core, name, props);
 
     if (v->stream == NULL) {
         goto error;
@@ -563,7 +588,11 @@ qpw_init_out(HWVoiceOut *hw, struct audsettings *as, void 
*drv_opaque)
     audio_pcm_init_info(&hw->info, &obt_as);
 
     /* report the buffer size to qemu */
-    hw->samples = BUFFER_SAMPLES;
+    hw->samples = audio_buffer_frames(
+        qapi_AudiodevPipewirePerDirectionOptions_base(ppdo), &obt_as, 46440);
+    v->highwater_mark = MIN(RINGBUFFER_SIZE,
+                            (ppdo->has_latency ? ppdo->latency : 46440)
+                            * (uint64_t)v->info.rate / 1000000 * 
v->frame_size);
 
     pw_thread_loop_unlock(c->thread_loop);
     return 0;
@@ -606,7 +635,8 @@ qpw_init_in(HWVoiceIn *hw, struct audsettings *as, void 
*drv_opaque)
     audio_pcm_init_info(&hw->info, &obt_as);
 
     /* report the buffer size to qemu */
-    hw->samples = BUFFER_SAMPLES;
+    hw->samples = audio_buffer_frames(
+        qapi_AudiodevPipewirePerDirectionOptions_base(ppdo), &obt_as, 46440);
 
     pw_thread_loop_unlock(c->thread_loop);
     return 0;
@@ -695,15 +725,8 @@ qpw_audio_init(Audiodev *dev)
     pw = g_new0(pwaudio, 1);
     pw_init(NULL, NULL);
 
-    AudiodevPipewireOptions *popts;
     trace_pw_audio_init("Initialize Pipewire context\n");
     assert(dev->driver == AUDIODEV_DRIVER_PIPEWIRE);
-    popts = &dev->u.pipewire;
-
-    if (!popts->has_latency) {
-        popts->has_latency = true;
-        popts->latency = 15000;
-    }
 
     pw->dev = dev;
     pw->thread_loop = pw_thread_loop_new("Pipewire thread loop", NULL);
@@ -781,7 +804,7 @@ static struct audio_pcm_ops qpw_pcm_ops = {
     .init_out = qpw_init_out,
     .fini_out = qpw_fini_out,
     .write = qpw_write,
-    .buffer_get_free = audio_generic_buffer_get_free,
+    .buffer_get_free = qpw_buffer_get_free,
     .run_buffer_out = audio_generic_run_buffer_out,
     .enable_out = qpw_enable_out,
 
diff --git a/qapi/audio.json b/qapi/audio.json
index 9a0d7d9ece..d49a8a670b 100644
--- a/qapi/audio.json
+++ b/qapi/audio.json
@@ -337,6 +337,7 @@
 #               create multiple Pipewire devices or run multiple qemu
 #               instances (default: audiodev's id, since 7.1)
 #
+# @latency: Pipewire backend buffer size in microseconds (default 46440)
 #
 # Since: 8.0
 ##
@@ -344,7 +345,8 @@
   'base': 'AudiodevPerDirectionOptions',
   'data': {
     '*name': 'str',
-    '*stream-name': 'str' } }
+    '*stream-name': 'str',
+    '*latency': 'uint32' } }
 
 ##
 # @AudiodevPipewireOptions:
@@ -355,16 +357,12 @@
 #
 # @out: options of the playback stream
 #
-# @latency: add latency to playback in microseconds
-#           (default 15000)
-#
 # Since: 8.0
 ##
 { 'struct': 'AudiodevPipewireOptions',
   'data': {
     '*in':     'AudiodevPipewirePerDirectionOptions',
-    '*out':    'AudiodevPipewirePerDirectionOptions',
-    '*latency': 'uint32' } }
+    '*out':    'AudiodevPipewirePerDirectionOptions' } }
 
 ##
 # @AudiodevSdlPerDirectionOptions:
-- 
2.35.3