The driver implements a message-based transport for I/O substream
operations. Before the start of the substream, the hardware buffer is
sliced into I/O messages, the number of which is equal to the current
number of periods. The size of each message is equal to the current
size of one period.
I/O messages are organized in an ordered queue. The completion of the
I/O message indicates an elapsed period (the only exception is the end
of the stream for the capture substream). Upon completion, the message
is automatically re-added to the end of the queue.
Signed-off-by: Anton Yakovlev <[email protected]>
---
sound/virtio/Makefile | 3 +-
sound/virtio/virtio_card.c | 18 +-
sound/virtio/virtio_card.h | 9 +
sound/virtio/virtio_pcm.c | 32 +++
sound/virtio/virtio_pcm.h | 42 ++++
sound/virtio/virtio_pcm_msg.c | 392 ++++++++++++++++++++++++++++++++++
6 files changed, 493 insertions(+), 3 deletions(-)
create mode 100644 sound/virtio/virtio_pcm_msg.c
diff --git a/sound/virtio/Makefile b/sound/virtio/Makefile
index 69162a545a41..626af3cc3ed7 100644
--- a/sound/virtio/Makefile
+++ b/sound/virtio/Makefile
@@ -5,5 +5,6 @@ obj-$(CONFIG_SND_VIRTIO) += virtio_snd.o
virtio_snd-objs := \
virtio_card.o \
virtio_ctl_msg.o \
- virtio_pcm.o
+ virtio_pcm.o \
+ virtio_pcm_msg.o
diff --git a/sound/virtio/virtio_card.c b/sound/virtio/virtio_card.c
index 235afc25fce7..a845978111d6 100644
--- a/sound/virtio/virtio_card.c
+++ b/sound/virtio/virtio_card.c
@@ -65,8 +65,16 @@ static void virtsnd_event_notify_cb(struct virtqueue *vqueue)
spin_lock_irqsave(&queue->lock, flags);
do {
virtqueue_disable_cb(vqueue);
- while ((event = virtqueue_get_buf(vqueue, &length)))
+ while ((event = virtqueue_get_buf(vqueue, &length))) {
+ switch (le32_to_cpu(event->hdr.code)) {
+ case VIRTIO_SND_EVT_PCM_PERIOD_ELAPSED:
+ case VIRTIO_SND_EVT_PCM_XRUN:
+ virtsnd_pcm_event(snd, event);
+ break;
+ }
+
virtsnd_event_send(vqueue, event, true, GFP_ATOMIC);
+ }
if (unlikely(virtqueue_is_broken(vqueue)))
break;
} while (!virtqueue_enable_cb(vqueue));
@@ -87,7 +95,9 @@ static int virtsnd_find_vqs(struct virtio_snd *snd)
struct virtio_device *vdev = snd->vdev;
vq_callback_t *callbacks[VIRTIO_SND_VQ_MAX] = {
[VIRTIO_SND_VQ_CONTROL] = virtsnd_ctl_notify_cb,
- [VIRTIO_SND_VQ_EVENT] = virtsnd_event_notify_cb
+ [VIRTIO_SND_VQ_EVENT] = virtsnd_event_notify_cb,
+ [VIRTIO_SND_VQ_TX] = virtsnd_pcm_tx_notify_cb,
+ [VIRTIO_SND_VQ_RX] = virtsnd_pcm_rx_notify_cb
};
const char *names[VIRTIO_SND_VQ_MAX] = {
[VIRTIO_SND_VQ_CONTROL] = "virtsnd-ctl",
@@ -299,6 +309,7 @@ static int virtsnd_probe(struct virtio_device *vdev)
static void virtsnd_remove(struct virtio_device *vdev)
{
struct virtio_snd *snd = vdev->priv;
+ unsigned int i;
/* Stop all the virtqueues. */
vdev->config->reset(vdev);
@@ -310,6 +321,9 @@ static void virtsnd_remove(struct virtio_device *vdev)
vdev->config->del_vqs(vdev);
+ for (i = 0; snd->substreams && i < snd->nsubstreams; ++i)
+ virtsnd_pcm_msg_free(&snd->substreams[i]);
+
kfree(snd->event_msgs);
}
diff --git a/sound/virtio/virtio_card.h b/sound/virtio/virtio_card.h
index f5e06a1ec033..3d8f5ad92f79 100644
--- a/sound/virtio/virtio_card.h
+++ b/sound/virtio/virtio_card.h
@@ -81,4 +81,13 @@ virtsnd_rx_queue(struct virtio_snd *snd)
return &snd->queues[VIRTIO_SND_VQ_RX];
}
+static inline struct virtio_snd_queue *
+virtsnd_pcm_queue(struct virtio_pcm_substream *vss)
+{
+ if (vss->direction == SNDRV_PCM_STREAM_PLAYBACK)
+ return virtsnd_tx_queue(vss->snd);
+ else
+ return virtsnd_rx_queue(vss->snd);
+}
+
#endif /* VIRTIO_SND_CARD_H */
diff --git a/sound/virtio/virtio_pcm.c b/sound/virtio/virtio_pcm.c
index 4348ead63c14..3cfd3520a9c0 100644
--- a/sound/virtio/virtio_pcm.c
+++ b/sound/virtio/virtio_pcm.c
@@ -337,6 +337,8 @@ int virtsnd_pcm_parse_cfg(struct virtio_snd *snd)
vss->snd = snd;
vss->sid = i;
+ init_waitqueue_head(&vss->msg_empty);
+ spin_lock_init(&vss->lock);
rc = virtsnd_pcm_build_hw(vss, &info[i]);
if (rc)
@@ -461,3 +463,33 @@ int virtsnd_pcm_build_devs(struct virtio_snd *snd)
return 0;
}
+
+/**
+ * virtsnd_pcm_event() - Handle the PCM device event notification.
+ * @snd: VirtIO sound device.
+ * @event: VirtIO sound event.
+ *
+ * Context: Interrupt context.
+ */
+void virtsnd_pcm_event(struct virtio_snd *snd, struct virtio_snd_event *event)
+{
+ struct virtio_pcm_substream *vss;
+ u32 sid = le32_to_cpu(event->data);
+
+ if (sid >= snd->nsubstreams)
+ return;
+
+ vss = &snd->substreams[sid];
+
+ switch (le32_to_cpu(event->hdr.code)) {
+ case VIRTIO_SND_EVT_PCM_PERIOD_ELAPSED:
+ /* TODO: deal with shmem elapsed period */
+ break;
+ case VIRTIO_SND_EVT_PCM_XRUN:
+ spin_lock(&vss->lock);
+ if (vss->xfer_enabled)
+ vss->xfer_xrun = true;
+ spin_unlock(&vss->lock);
+ break;
+ }
+}
diff --git a/sound/virtio/virtio_pcm.h b/sound/virtio/virtio_pcm.h
index a2aadc44dce9..c70e4fed9044 100644
--- a/sound/virtio/virtio_pcm.h
+++ b/sound/virtio/virtio_pcm.h
@@ -22,6 +22,19 @@ struct virtio_pcm_msg;
* @features: Stream VirtIO feature bit map (1 << VIRTIO_SND_PCM_F_XXX).
* @substream: Kernel ALSA substream.
* @hw: Kernel ALSA substream hardware descriptor.
+ * @frame_bytes: Current frame size in bytes.
+ * @period_size: Current period size in frames.
+ * @buffer_size: Current buffer size in frames.
+ * @lock: Spinlock that protects fields shared by interrupt handlers and
+ * substream operators.
+ * @hw_ptr: Substream hardware pointer value in frames [0 ... buffer_size).
+ * @xfer_enabled: Data transfer state (0 - off, 1 - on).
+ * @xfer_xrun: Data underflow/overflow state (0 - no xrun, 1 - xrun).
+ * @msgs: Allocated I/O messages.
+ * @nmsgs: Number of allocated I/O messages.
+ * @msg_last_enqueued: Index of the last I/O message added to the virtqueue.
+ * @msg_count: Number of pending I/O messages in the virtqueue.
+ * @msg_empty: Notify when msg_count is zero.
*/
struct virtio_pcm_substream {
struct virtio_snd *snd;
@@ -31,6 +44,18 @@ struct virtio_pcm_substream {
u32 features;
struct snd_pcm_substream *substream;
struct snd_pcm_hardware hw;
+ unsigned int frame_bytes;
+ snd_pcm_uframes_t period_size;
+ snd_pcm_uframes_t buffer_size;
+ spinlock_t lock;
+ snd_pcm_uframes_t hw_ptr;
+ bool xfer_enabled;
+ bool xfer_xrun;
+ struct virtio_pcm_msg **msgs;
+ unsigned int nmsgs;
+ int msg_last_enqueued;
+ unsigned int msg_count;
+ wait_queue_head_t msg_empty;
};
/**
@@ -63,8 +88,25 @@ int virtsnd_pcm_parse_cfg(struct virtio_snd *snd);
int virtsnd_pcm_build_devs(struct virtio_snd *snd);
+void virtsnd_pcm_event(struct virtio_snd *snd, struct virtio_snd_event *event);
+
+void virtsnd_pcm_tx_notify_cb(struct virtqueue *vqueue);
+
+void virtsnd_pcm_rx_notify_cb(struct virtqueue *vqueue);
+
struct virtio_pcm *virtsnd_pcm_find(struct virtio_snd *snd, u32 nid);
struct virtio_pcm *virtsnd_pcm_find_or_create(struct virtio_snd *snd, u32 nid);
+struct virtio_snd_msg *
+virtsnd_pcm_ctl_msg_alloc(struct virtio_pcm_substream *vss,
+ unsigned int command, gfp_t gfp);
+
+int virtsnd_pcm_msg_alloc(struct virtio_pcm_substream *vss,
+ unsigned int periods, unsigned int period_bytes);
+
+void virtsnd_pcm_msg_free(struct virtio_pcm_substream *vss);
+
+int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss);
+
#endif /* VIRTIO_SND_PCM_H */
diff --git a/sound/virtio/virtio_pcm_msg.c b/sound/virtio/virtio_pcm_msg.c
new file mode 100644
index 000000000000..8f29a9baf806
--- /dev/null
+++ b/sound/virtio/virtio_pcm_msg.c
@@ -0,0 +1,392 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * virtio-snd: Virtio sound device
+ * Copyright (C) 2021 OpenSynergy GmbH
+ */
+#include <sound/pcm_params.h>
+
+#include "virtio_card.h"
+
+/**
+ * struct virtio_pcm_msg - VirtIO I/O message.
+ * @substream: VirtIO PCM substream.
+ * @xfer: Request header payload.
+ * @status: Response header payload.
+ * @sgs: Payload scatter-gather table.
+ */
+struct virtio_pcm_msg {
+ struct virtio_pcm_substream *substream;
+ struct virtio_snd_pcm_xfer xfer;
+ struct virtio_snd_pcm_status status;
+ struct scatterlist sgs[0];
+};
+
+/**
+ * enum pcm_msg_sg_index - Index values for the virtio_pcm_msg->sgs field in
+ * an I/O message.
+ * @PCM_MSG_SG_XFER: Element containing a virtio_snd_pcm_xfer structure.
+ * @PCM_MSG_SG_STATUS: Element containing a virtio_snd_pcm_status structure.
+ * @PCM_MSG_SG_DATA: The first element containing a data buffer.
+ */
+enum pcm_msg_sg_index {
+ PCM_MSG_SG_XFER = 0,
+ PCM_MSG_SG_STATUS,
+ PCM_MSG_SG_DATA
+};
+
+/**
+ * virtsnd_pcm_sg_num() - Count the number of sg-elements required to represent
+ * vmalloc'ed buffer.
+ * @data: Pointer to vmalloc'ed buffer.
+ * @length: Buffer size.
+ *
+ * Context: Any context.
+ * Return: Number of physically contiguous parts in the @data.
+ */
+static int virtsnd_pcm_sg_num(u8 *data, unsigned int length)
+{
+ phys_addr_t sg_address;
+ unsigned int sg_length;
+ int num = 0;
+
+ while (length) {
+ struct page *pg = vmalloc_to_page(data);
+ phys_addr_t pg_address = page_to_phys(pg);
+ size_t pg_length;
+
+ pg_length = PAGE_SIZE - offset_in_page(data);
+ if (pg_length > length)
+ pg_length = length;
+
+ if (!num || sg_address + sg_length != pg_address) {
+ sg_address = pg_address;
+ sg_length = pg_length;
+ num++;
+ } else {
+ sg_length += pg_length;
+ }
+
+ data += pg_length;
+ length -= pg_length;
+ }
+
+ return num;
+}
+
+/**
+ * virtsnd_pcm_sg_from() - Build sg-list from vmalloc'ed buffer.
+ * @sgs: Preallocated sg-list to populate.
+ * @nsgs: The maximum number of elements in the @sgs.
+ * @data: Pointer to vmalloc'ed buffer.
+ * @length: Buffer size.
+ *
+ * Splits the buffer into physically contiguous parts and makes an sg-list of
+ * such parts.
+ *
+ * Context: Any context.
+ */
+static void virtsnd_pcm_sg_from(struct scatterlist *sgs, int nsgs, u8 *data,
+ unsigned int length)
+{
+ int idx = -1;
+
+ while (length) {
+ struct page *pg = vmalloc_to_page(data);
+ size_t pg_length;
+
+ pg_length = PAGE_SIZE - offset_in_page(data);
+ if (pg_length > length)
+ pg_length = length;
+
+ if (idx == -1 ||
+ sg_phys(&sgs[idx]) + sgs[idx].length != page_to_phys(pg)) {
+ if (idx + 1 == nsgs)
+ break;
+ sg_set_page(&sgs[++idx], pg, pg_length,
+ offset_in_page(data));
+ } else {
+ sgs[idx].length += pg_length;
+ }
+
+ data += pg_length;
+ length -= pg_length;
+ }
+
+ sg_mark_end(&sgs[idx]);
+}
+
+/**
+ * virtsnd_pcm_msg_alloc() - Allocate I/O messages.
+ * @vss: VirtIO PCM substream.
+ * @periods: Current number of periods.
+ * @period_bytes: Current period size in bytes.
+ *
+ * The function slices the buffer into @periods parts (each with the size of
+ * @period_bytes), and creates @periods corresponding I/O messages.
+ *
+ * Context: Any context that permits to sleep.
+ * Return: 0 on success, -ENOMEM on failure.
+ */
+int virtsnd_pcm_msg_alloc(struct virtio_pcm_substream *vss,
+ unsigned int periods, unsigned int period_bytes)
+{
+ struct snd_pcm_runtime *runtime = vss->substream->runtime;
+ unsigned int i;
+
+ /* Free previously allocated messages (if any). */
+ virtsnd_pcm_msg_free(vss);
+
+ vss->msgs = kcalloc(periods, sizeof(*vss->msgs), GFP_KERNEL);
+ if (!vss->msgs)
+ return -ENOMEM;
+
+ vss->nmsgs = periods;
+
+ for (i = 0; i < periods; ++i) {
+ u8 *data = runtime->dma_area + period_bytes * i;
+ int sg_num = virtsnd_pcm_sg_num(data, period_bytes);
+ struct virtio_pcm_msg *msg;
+
+ msg = kzalloc(sizeof(*msg) + sizeof(*msg->sgs) * (sg_num + 2),
+ GFP_KERNEL);
+ if (!msg)
+ return -ENOMEM;
+
+ msg->substream = vss;
+ sg_init_one(&msg->sgs[PCM_MSG_SG_XFER], &msg->xfer,
+ sizeof(msg->xfer));
+ sg_init_one(&msg->sgs[PCM_MSG_SG_STATUS], &msg->status,
+ sizeof(msg->status));
+ virtsnd_pcm_sg_from(&msg->sgs[PCM_MSG_SG_DATA], sg_num, data,
+ period_bytes);
+
+ vss->msgs[i] = msg;
+ }
+
+ return 0;
+}
+
+/**
+ * virtsnd_pcm_msg_free() - Free all allocated I/O messages.
+ * @vss: VirtIO PCM substream.
+ *
+ * Context: Any context.
+ */
+void virtsnd_pcm_msg_free(struct virtio_pcm_substream *vss)
+{
+ unsigned int i;
+
+ for (i = 0; i < vss->nmsgs; ++i)
+ kfree(vss->msgs[i]);
+ kfree(vss->msgs);
+
+ vss->msgs = NULL;
+ vss->nmsgs = 0;
+}
+
+/**
+ * virtsnd_pcm_msg_send() - Send asynchronous I/O messages.
+ * @vss: VirtIO PCM substream.
+ *
+ * All messages are organized in an ordered circular list. Each time the
+ * function is called, all currently non-enqueued messages are added to the
+ * virtqueue. For this, the function keeps track of two values:
+ *
+ * msg_last_enqueued = index of the last enqueued message,
+ * msg_count = # of pending messages in the virtqueue.
+ *
+ * Context: Any context. Expects the tx/rx queue and the VirtIO substream
+ * spinlocks to be held by caller.
+ * Return: 0 on success, -errno on failure.
+ */
+int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss)
+{
+ struct snd_pcm_runtime *runtime = vss->substream->runtime;
+ struct virtio_snd *snd = vss->snd;
+ struct virtio_device *vdev = snd->vdev;
+ struct virtqueue *vqueue = virtsnd_pcm_queue(vss)->vqueue;
+ int i;
+ int n;
+ bool notify = false;
+
+ i = (vss->msg_last_enqueued + 1) % runtime->periods;
+ n = runtime->periods - vss->msg_count;
+
+ for (; n; --n, i = (i + 1) % runtime->periods) {
+ struct virtio_pcm_msg *msg = vss->msgs[i];
+ struct scatterlist *psgs[] = {
+ &msg->sgs[PCM_MSG_SG_XFER],
+ &msg->sgs[PCM_MSG_SG_DATA],
+ &msg->sgs[PCM_MSG_SG_STATUS]
+ };
+ int rc;
+
+ msg->xfer.stream_id = cpu_to_le32(vss->sid);
+ memset(&msg->status, 0, sizeof(msg->status));
+
+ if (vss->direction == SNDRV_PCM_STREAM_PLAYBACK)
+ rc = virtqueue_add_sgs(vqueue, psgs, 2, 1, msg,
+ GFP_ATOMIC);
+ else
+ rc = virtqueue_add_sgs(vqueue, psgs, 1, 2, msg,
+ GFP_ATOMIC);
+
+ if (rc) {
+ dev_err(&vdev->dev,
+ "SID %u: failed to send I/O message\n",
+ vss->sid);
+ return rc;
+ }
+
+ vss->msg_last_enqueued = i;
+ vss->msg_count++;
+ }
+
+ if (!(vss->features & (1U << VIRTIO_SND_PCM_F_MSG_POLLING)))
+ notify = virtqueue_kick_prepare(vqueue);
+
+ if (notify)
+ virtqueue_notify(vqueue);
+
+ return 0;
+}
+
+/**
+ * virtsnd_pcm_msg_complete() - Complete an I/O message.
+ * @msg: I/O message.
+ * @size: Number of bytes written.
+ *
+ * Completion of the message means the elapsed period.
+ *
+ * Context: Interrupt context. Takes and releases the VirtIO substream spinlock.
+ */
+static void virtsnd_pcm_msg_complete(struct virtio_pcm_msg *msg, size_t size)
+{
+ struct virtio_pcm_substream *vss = msg->substream;
+
+ /*
+ * hw_ptr always indicates the buffer position of the first I/O message
+ * in the virtqueue. Therefore, on each completion of an I/O message,
+ * the hw_ptr value is unconditionally advanced.
+ */
+ spin_lock(&vss->lock);
+ /*
+ * If the capture substream returned an incorrect status, then just
+ * increase the hw_ptr by the period size.
+ */
+ if (vss->direction == SNDRV_PCM_STREAM_PLAYBACK ||
+ size <= sizeof(msg->status)) {
+ vss->hw_ptr += vss->period_size;
+ } else {
+ size -= sizeof(msg->status);
+ vss->hw_ptr += size / vss->frame_bytes;
+ }
+
+ vss->hw_ptr %= vss->buffer_size;
+ vss->xfer_xrun = false;
+ vss->msg_count--;
+
+ if (vss->xfer_enabled) {
+ struct snd_pcm_runtime *runtime = vss->substream->runtime;
+
+ runtime->delay =
+ bytes_to_frames(runtime,
+ le32_to_cpu(msg->status.latency_bytes));
+
+ spin_unlock(&vss->lock);
+ snd_pcm_period_elapsed(vss->substream);
+ spin_lock(&vss->lock);
+
+ virtsnd_pcm_msg_send(vss);
+ } else if (!vss->msg_count) {
+ wake_up_all(&vss->msg_empty);
+ }
+ spin_unlock(&vss->lock);
+}
+
+/**
+ * virtsnd_pcm_notify_cb() - Process all completed I/O messages.
+ * @queue: Underlying tx/rx virtqueue.
+ *
+ * If transmission is allowed, then each completed message is immediately placed
+ * back at the end of the queue.
+ *
+ * Context: Interrupt context. Takes and releases the tx/rx queue spinlock.
+ */
+static inline void virtsnd_pcm_notify_cb(struct virtio_snd_queue *queue)
+{
+ struct virtio_pcm_msg *msg;
+ u32 length;
+ unsigned long flags;
+
+ spin_lock_irqsave(&queue->lock, flags);
+ do {
+ virtqueue_disable_cb(queue->vqueue);
+ while ((msg = virtqueue_get_buf(queue->vqueue, &length)))
+ virtsnd_pcm_msg_complete(msg, length);
+ if (unlikely(virtqueue_is_broken(queue->vqueue)))
+ break;
+ } while (!virtqueue_enable_cb(queue->vqueue));
+ spin_unlock_irqrestore(&queue->lock, flags);
+}
+
+/**
+ * virtsnd_pcm_tx_notify_cb() - Process all completed TX messages.
+ * @vqueue: Underlying tx virtqueue.
+ *
+ * Context: Interrupt context.
+ */
+void virtsnd_pcm_tx_notify_cb(struct virtqueue *vqueue)
+{
+ struct virtio_snd *snd = vqueue->vdev->priv;
+
+ virtsnd_pcm_notify_cb(virtsnd_tx_queue(snd));
+}
+
+/**
+ * virtsnd_pcm_rx_notify_cb() - Process all completed RX messages.
+ * @vqueue: Underlying rx virtqueue.
+ *
+ * Context: Interrupt context.
+ */
+void virtsnd_pcm_rx_notify_cb(struct virtqueue *vqueue)
+{
+ struct virtio_snd *snd = vqueue->vdev->priv;
+
+ virtsnd_pcm_notify_cb(virtsnd_rx_queue(snd));
+}
+
+/**
+ * virtsnd_pcm_ctl_msg_alloc() - Allocate and initialize the PCM device control
+ * message for the specified substream.
+ * @vss: VirtIO PCM substream.
+ * @command: Control request code (VIRTIO_SND_R_PCM_XXX).
+ * @gfp: Kernel flags for memory allocation.
+ *
+ * Context: Any context. May sleep if @gfp flags permit.
+ * Return: Allocated message on success, NULL on failure.
+ */
+struct virtio_snd_msg *
+virtsnd_pcm_ctl_msg_alloc(struct virtio_pcm_substream *vss,
+ unsigned int command, gfp_t gfp)
+{
+ size_t request_size = sizeof(struct virtio_snd_pcm_hdr);
+ size_t response_size = sizeof(struct virtio_snd_hdr);
+ struct virtio_snd_msg *msg;
+
+ switch (command) {
+ case VIRTIO_SND_R_PCM_SET_PARAMS:
+ request_size = sizeof(struct virtio_snd_pcm_set_params);
+ break;
+ }
+
+ msg = virtsnd_ctl_msg_alloc(request_size, response_size, gfp);
+ if (msg) {
+ struct virtio_snd_pcm_hdr *hdr = virtsnd_ctl_msg_request(msg);
+
+ hdr->hdr.code = cpu_to_le32(command);
+ hdr->stream_id = cpu_to_le32(vss->sid);
+ }
+
+ return msg;
+}
--
2.30.0
On Mon, 22 Feb 2021 16:34:40 +0100,
Anton Yakovlev wrote:
>
> +void virtsnd_pcm_event(struct virtio_snd *snd, struct virtio_snd_event *event)
> +{
> + struct virtio_pcm_substream *vss;
> + u32 sid = le32_to_cpu(event->data);
> +
> + if (sid >= snd->nsubstreams)
> + return;
> +
> + vss = &snd->substreams[sid];
> +
> + switch (le32_to_cpu(event->hdr.code)) {
> + case VIRTIO_SND_EVT_PCM_PERIOD_ELAPSED:
> + /* TODO: deal with shmem elapsed period */
> + break;
> + case VIRTIO_SND_EVT_PCM_XRUN:
> + spin_lock(&vss->lock);
> + if (vss->xfer_enabled)
> + vss->xfer_xrun = true;
> + spin_unlock(&vss->lock);
You can stop the stream at xrun, too.
But it often messes up with the locking, so it's no mandatory
implementation. You seem to pass the xrun state at the pointer
callback, and this should be enough for normal uses.
thanks,
Takashi