audio/pw: improve channel position code

Follow PulseAudio backend comment and code, and only implement the
channels QEMU actually supports at this point, and add the same comment
about limits and future mappings. Simplify a bit the code.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Volker Rümelin <vr_qemu@t-online.de>
Message-Id: <20230506163735.3481387-13-marcandre.lureau@redhat.com>

audio/pwaudio.c

@@ -417,8 +417,8 @@ pw_to_audfmt(enum spa_audio_format fmt, int *endianness,
 }
 
 static int
-create_stream(pwaudio *c, PWVoice *v, const char *stream_name,
-              const char *name, enum spa_direction dir)
+qpw_stream_new(pwaudio *c, PWVoice *v, const char *stream_name,
+               const char *name, enum spa_direction dir)
 {
     int res;
     uint32_t n_params;
@@ -482,62 +482,37 @@ create_stream(pwaudio *c, PWVoice *v, const char *stream_name,
     return 0;
 }
 
-static int
-qpw_stream_new(pwaudio *c, PWVoice *v, const char *stream_name,
-               const char *name, enum spa_direction dir)
+static void
+qpw_set_position(uint32_t channels, uint32_t position[SPA_AUDIO_MAX_CHANNELS])
 {
-    switch (v->info.channels) {
+    memcpy(position, (uint32_t[SPA_AUDIO_MAX_CHANNELS]) { SPA_AUDIO_CHANNEL_UNKNOWN, },
+           sizeof(uint32_t) * SPA_AUDIO_MAX_CHANNELS);
+    /*
+     * TODO: This currently expects the only frontend supporting more than 2
+     * channels is the usb-audio.  We will need some means to set channel
+     * order when a new frontend gains multi-channel support.
+     */
+    switch (channels) {
     case 8:
-        v->info.position[0] = SPA_AUDIO_CHANNEL_FL;
-        v->info.position[1] = SPA_AUDIO_CHANNEL_FR;
-        v->info.position[2] = SPA_AUDIO_CHANNEL_FC;
-        v->info.position[3] = SPA_AUDIO_CHANNEL_LFE;
-        v->info.position[4] = SPA_AUDIO_CHANNEL_RL;
-        v->info.position[5] = SPA_AUDIO_CHANNEL_RR;
-        v->info.position[6] = SPA_AUDIO_CHANNEL_SL;
-        v->info.position[7] = SPA_AUDIO_CHANNEL_SR;
-        break;
+        position[6] = SPA_AUDIO_CHANNEL_SL;
+        position[7] = SPA_AUDIO_CHANNEL_SR;
+        /* fallthrough */
     case 6:
-        v->info.position[0] = SPA_AUDIO_CHANNEL_FL;
-        v->info.position[1] = SPA_AUDIO_CHANNEL_FR;
-        v->info.position[2] = SPA_AUDIO_CHANNEL_FC;
-        v->info.position[3] = SPA_AUDIO_CHANNEL_LFE;
-        v->info.position[4] = SPA_AUDIO_CHANNEL_RL;
-        v->info.position[5] = SPA_AUDIO_CHANNEL_RR;
-        break;
-    case 5:
-        v->info.position[0] = SPA_AUDIO_CHANNEL_FL;
-        v->info.position[1] = SPA_AUDIO_CHANNEL_FR;
-        v->info.position[2] = SPA_AUDIO_CHANNEL_FC;
-        v->info.position[3] = SPA_AUDIO_CHANNEL_LFE;
-        v->info.position[4] = SPA_AUDIO_CHANNEL_RC;
-        break;
-    case 4:
-        v->info.position[0] = SPA_AUDIO_CHANNEL_FL;
-        v->info.position[1] = SPA_AUDIO_CHANNEL_FR;
-        v->info.position[2] = SPA_AUDIO_CHANNEL_FC;
-        v->info.position[3] = SPA_AUDIO_CHANNEL_RC;
-        break;
-    case 3:
-        v->info.position[0] = SPA_AUDIO_CHANNEL_FL;
-        v->info.position[1] = SPA_AUDIO_CHANNEL_FR;
-        v->info.position[2] = SPA_AUDIO_CHANNEL_LFE;
-        break;
+        position[2] = SPA_AUDIO_CHANNEL_FC;
+        position[3] = SPA_AUDIO_CHANNEL_LFE;
+        position[4] = SPA_AUDIO_CHANNEL_RL;
+        position[5] = SPA_AUDIO_CHANNEL_RR;
+        /* fallthrough */
     case 2:
-        v->info.position[0] = SPA_AUDIO_CHANNEL_FL;
-        v->info.position[1] = SPA_AUDIO_CHANNEL_FR;
+        position[0] = SPA_AUDIO_CHANNEL_FL;
+        position[1] = SPA_AUDIO_CHANNEL_FR;
         break;
     case 1:
-        v->info.position[0] = SPA_AUDIO_CHANNEL_MONO;
+        position[0] = SPA_AUDIO_CHANNEL_MONO;
         break;
     default:
-        for (size_t i = 0; i < v->info.channels; i++) {
-            v->info.position[i] = SPA_AUDIO_CHANNEL_UNKNOWN;
-        }
-        break;
+        dolog("Internal error: unsupported channel count %d\n", channels);
     }
-
-    return create_stream(c, v, stream_name, name, dir);
 }
 
 static int
@@ -555,6 +530,7 @@ qpw_init_out(HWVoiceOut *hw, struct audsettings *as, void *drv_opaque)
 
     v->info.format = audfmt_to_pw(as->fmt, as->endianness);
     v->info.channels = as->nchannels;
+    qpw_set_position(as->nchannels, v->info.position);
     v->info.rate = as->freq;
 
     obt_as.fmt =
@@ -601,6 +577,7 @@ qpw_init_in(HWVoiceIn *hw, struct audsettings *as, void *drv_opaque)
 
     v->info.format = audfmt_to_pw(as->fmt, as->endianness);
     v->info.channels = as->nchannels;
+    qpw_set_position(as->nchannels, v->info.position);
     v->info.rate = as->freq;
 
     obt_as.fmt =