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Author: Cuda-Chen

virtio-snd.c

@@ -499,11 +499,19 @@ static void virtio_snd_read_pcm_prepare(const virtio_snd_pcm_hdr_t *query,
     uint32_t channels = props->pp.channels;
     uint32_t rate = pcm_rate_tbl[props->pp.rate];
 
-    // Calculate bps rate
+    /* Rather use the period_bytes/buffer_bytes set by driver,
+     * we calculate bps rate to achieve the strema's desired parameters
+     * suggested by [1].
+     */
+    /* Reference:
+     * [1]
+     * https://github.com/rust-vmm/vhost-device/blob/main/vhost-device-sound/src/audio_backends/alsa.rs#L153
+     */
+    /* Calculate bps rate. */
     uint32_t bps_rate = channels * VSND_CNFA_FRAME_SZ * rate;
-    // Calculate period bytes for ~100ms interrupt period
+    /* Calculate period bytes for ~100ms interrupt period. */
     uint32_t cnfa_period_bytes = bps_rate / 10;
-    // Calculate the period size (in frames) for CNFA
+    /* Calculate the period size (in frames) for CNFA . */
     uint32_t cnfa_period_frames = cnfa_period_bytes / VSND_CNFA_FRAME_SZ;
     uint32_t period_frames = period_bytes / VSND_CNFA_FRAME_SZ;
 
@@ -774,8 +782,17 @@ static void __virtio_snd_frame_enqueue(void *payload,
         pthread_cond_wait(&props->lock.writable, &props->lock.lock);
 
     /* Add a PCM frame to queue */
-    /* TODO: add description of the speciality of Linux Kernel VirtIO sound
-     * driver */
+    /* As stated in Linux Kernel mailing list [1], we keep the pointer
+     * points to the payload [2] so that we can always get up-to-date
+     * contents of PCM frames.
+     * References:
+     * [1] https://lore.kernel.org/all/[email protected]/T/
+     * [2]
+     * https://github.com/rust-vmm/vhost-device/blob/eb2e2227e41d48a52e4e6346189b772c5363879d/staging/vhost-device-sound/src/device.rs#L554
+     */
+    /* FIXME: locate the root case of repeating artifact even we
+     * keep the pointer of the payload.
+     */
     vsnd_buf_queue_node_t *node = malloc(sizeof(*node));
     node->addr = payload;
     node->len = n;