Re: [PATCH v2 6/9] ALSA: virtio: PCM substream operators

On Sun, 24 Jan 2021, Anton Yakovlev wrote:

Introduce the operators required for the operation of substreams.

Signed-off-by: Anton Yakovlev anton.yakovlev@opensynergy.com

sound/virtio/Makefile | 3 +- sound/virtio/virtio_pcm.c | 5 +- sound/virtio/virtio_pcm.h | 2 + sound/virtio/virtio_pcm_ops.c | 513 ++++++++++++++++++++++++++++++++++ 4 files changed, 521 insertions(+), 2 deletions(-) create mode 100644 sound/virtio/virtio_pcm_ops.c

[snip]

diff --git a/sound/virtio/virtio_pcm_ops.c b/sound/virtio/virtio_pcm_ops.c new file mode 100644 index 000000000000..19882777fcd6 --- /dev/null +++ b/sound/virtio/virtio_pcm_ops.c @@ -0,0 +1,513 @@

[snip]

+/**

• • virtsnd_pcm_release() - Release the PCM substream on the device side.
• • @substream: VirtIO substream.
• • Context: Any context that permits to sleep.
• • Return: 0 on success, -errno on failure.
• */

+static inline bool virtsnd_pcm_released(struct virtio_pcm_substream *substream) +{

• /*

• * The spec states that upon receipt of the RELEASE command "the device
  

• * MUST complete all pending I/O messages for the specified stream ID".
  

• * Thus, we consider the absence of I/O messages in the queue as an
  

• * indication that the substream has been released.
  

• */
  

• return atomic_read(&substream->msg_count) == 0;

Also here having it atomic doesn't really seem to help. This just means, that at some point of time it was == 0.

+}

+static int virtsnd_pcm_release(struct virtio_pcm_substream *substream)

kernel-doc missing

+{

• struct virtio_snd *snd = substream->snd;
• struct virtio_snd_msg *msg;
• unsigned int js = msecs_to_jiffies(msg_timeout_ms);
• int rc;
• msg = virtsnd_pcm_ctl_msg_alloc(substream, VIRTIO_SND_R_PCM_RELEASE,

• 			GFP_KERNEL);
  

• if (IS_ERR(msg))

• return PTR_ERR(msg);
  

• rc = virtsnd_ctl_msg_send_sync(snd, msg);
• if (rc)

• return rc;
  

• return wait_event_interruptible_timeout(substream->msg_empty,

• 				virtsnd_pcm_released(substream),
  

• 				js);
  

+}

+/**

• • virtsnd_pcm_open() - Open the PCM substream.
• • @substream: Kernel ALSA substream.
• • Context: Any context.
• • Return: 0 on success, -errno on failure.
• */

+static int virtsnd_pcm_open(struct snd_pcm_substream *substream) +{

• struct virtio_pcm *pcm = snd_pcm_substream_chip(substream);
• struct virtio_pcm_substream *ss = NULL;
• if (pcm) {

• switch (substream->stream) {
  

• case SNDRV_PCM_STREAM_PLAYBACK:
  

• case SNDRV_PCM_STREAM_CAPTURE: {
  

• 	struct virtio_pcm_stream *stream =
  

• 		&pcm->streams[substream->stream];
  

• 	if (substream->number < stream->nsubstreams)
  

Can this condition ever be false?

• 		ss = stream->substreams[substream->number];
  

• 	break;
  

• }
  

• }
  

• }
• if (!ss)

• return -EBADFD;
  

• substream->runtime->hw = ss->hw;
• substream->private_data = ss;
• return 0;

+}

+/**

• • virtsnd_pcm_close() - Close the PCM substream.
• • @substream: Kernel ALSA substream.
• • Context: Any context.
• • Return: 0.
• */

+static int virtsnd_pcm_close(struct snd_pcm_substream *substream) +{

• return 0;

+}

+/**

• • virtsnd_pcm_hw_params() - Set the parameters of the PCM substream.
• • @substream: Kernel ALSA substream.
• • @hw_params: Hardware parameters (can be NULL).
• • The function can be called both from the upper level (in this case,
• • @hw_params is not NULL) or from the driver itself (in this case, @hw_params
• • is NULL, and the parameter values are taken from the runtime structure).
• • In all cases, the function:
• • 1. checks the state of the virtqueue and, if necessary, tries to fix it,
• • 2. sets the parameters on the device side,
• • 3. allocates a hardware buffer and I/O messages.
• • Context: Any context that permits to sleep.
• • Return: 0 on success, -errno on failure.
• */

+static int virtsnd_pcm_hw_params(struct snd_pcm_substream *substream,

• 		 struct snd_pcm_hw_params *hw_params)
  

+{

• struct snd_pcm_runtime *runtime = substream->runtime;
• struct virtio_pcm_substream *ss = snd_pcm_substream_chip(substream);
• struct virtio_device *vdev = ss->snd->vdev;
• struct virtio_snd_msg *msg;
• struct virtio_snd_pcm_set_params *request;
• snd_pcm_format_t format;
• unsigned int channels;
• unsigned int rate;
• unsigned int buffer_bytes;
• unsigned int period_bytes;
• unsigned int periods;
• unsigned int i;
• int vformat = -1;
• int vrate = -1;
• int rc;
• /*

• * If we got here after ops->trigger() was called, the queue may
  

• * still contain messages. In this case, we need to release the
  

• * substream first.
  

• */
  

• if (atomic_read(&ss->msg_count)) {

• rc = virtsnd_pcm_release(ss);
  

• if (rc) {
  

• 	dev_err(&vdev->dev,
  

• 		"SID %u: invalid I/O queue state\n",
  

• 		ss->sid);
  

• 	return rc;
  

• }
  

• }
• /* Set hardware parameters in device */
• if (hw_params) {

• format = params_format(hw_params);
  

• channels = params_channels(hw_params);
  

• rate = params_rate(hw_params);
  

• buffer_bytes = params_buffer_bytes(hw_params);
  

• period_bytes = params_period_bytes(hw_params);
  

• periods = params_periods(hw_params);
  

• } else {

• format = runtime->format;
  

• channels = runtime->channels;
  

• rate = runtime->rate;
  

• buffer_bytes = frames_to_bytes(runtime, runtime->buffer_size);
  

• period_bytes = frames_to_bytes(runtime, runtime->period_size);
  

• periods = runtime->periods;
  

• }
• for (i = 0; i < ARRAY_SIZE(g_a2v_format_map); ++i)

• if (g_a2v_format_map[i].alsa_bit == format) {
  

• 	vformat = g_a2v_format_map[i].vio_bit;
  

• 	break;
  

• }
  

• for (i = 0; i < ARRAY_SIZE(g_a2v_rate_map); ++i)

• if (g_a2v_rate_map[i].rate == rate) {
  

• 	vrate = g_a2v_rate_map[i].vio_bit;
  

• 	break;
  

• }
  

• if (vformat == -1 || vrate == -1)

• return -EINVAL;
  

• msg = virtsnd_pcm_ctl_msg_alloc(ss, VIRTIO_SND_R_PCM_SET_PARAMS,

• 			GFP_KERNEL);
  

• if (IS_ERR(msg))

• return PTR_ERR(msg);
  

• request = sg_virt(&msg->sg_request);
• request->buffer_bytes = cpu_to_virtio32(vdev, buffer_bytes);
• request->period_bytes = cpu_to_virtio32(vdev, period_bytes);
• request->channels = channels;
• request->format = vformat;
• request->rate = vrate;

I presume the latter three fields don't have to be endienness-converted, perhaps they're 8-bit wide only.

• if (ss->features & (1U << VIRTIO_SND_PCM_F_MSG_POLLING))

• request->features |=
  

• 	cpu_to_virtio32(vdev,
  

• 			1U << VIRTIO_SND_PCM_F_MSG_POLLING);
  

• if (ss->features & (1U << VIRTIO_SND_PCM_F_EVT_XRUNS))

• request->features |=
  

• 	cpu_to_virtio32(vdev,
  

• 			1U << VIRTIO_SND_PCM_F_EVT_XRUNS);
  

• rc = virtsnd_ctl_msg_send_sync(ss->snd, msg);

Wouldn't it be better to only try to send the message after below allocations completed successfully?

• if (rc)

• return rc;
  

• /* If the buffer was already allocated earlier, do nothing. */
• if (runtime->dma_area)

• return 0;
  

• /* Allocate hardware buffer */
• rc = snd_pcm_lib_malloc_pages(substream, buffer_bytes);
• if (rc < 0)

• return rc;
  

• /* Allocate and initialize I/O messages */
• rc = virtsnd_pcm_msg_alloc(ss, periods, runtime->dma_area,

• 		   period_bytes);
  

• if (rc)

• snd_pcm_lib_free_pages(substream);
  

• return rc;

+}

+/**

• • virtsnd_pcm_hw_free() - Reset the parameters of the PCM substream.
• • @substream: Kernel ALSA substream.
• • The function does the following:
• • 1. tries to release the PCM substream on the device side,
• • 2. frees the hardware buffer.
• • Context: Any context that permits to sleep.
• • Return: 0 on success, -errno on failure.
• */

+static int virtsnd_pcm_hw_free(struct snd_pcm_substream *substream) +{

• struct virtio_pcm_substream *ss = snd_pcm_substream_chip(substream);
• int rc;
• rc = virtsnd_pcm_release(ss);
• /*

• * Even if we failed to send the RELEASE message or wait for the queue
  

• * flush to complete, we can safely delete the buffer. Because after
  

• * receiving the STOP command, the device must stop all I/O message
  

• * processing. If there are still pending messages in the queue, the
  

• * next ops->hw_params() call should deal with this.
  

• */
  

• snd_pcm_lib_free_pages(substream);
• return rc;

+}

+/**

• • virtsnd_pcm_hw_params() - Prepare the PCM substream.

copy-paste: this is virtsnd_pcm_prepare()

• • @substream: Kernel ALSA substream.
• • The function can be called both from the upper level or from the driver
• • itself.
• • In all cases, the function:
• • 1. checks the state of the virtqueue and, if necessary, tries to fix it,
• • 2. prepares the substream on the device side.
• • Context: Any context that permits to sleep. May take and release the tx/rx

• •      queue spinlock.
    

• • Return: 0 on success, -errno on failure.
• */

+static int virtsnd_pcm_prepare(struct snd_pcm_substream *substream) +{

• struct virtio_pcm_substream *ss = snd_pcm_substream_chip(substream);
• struct virtio_snd_queue *queue = virtsnd_pcm_queue(ss);
• struct virtio_snd_msg *msg;
• unsigned long flags;
• int rc;
• /*

• * If we got here after ops->trigger() was called, the queue may
  

• * still contain messages. In this case, we need to reset the
  

• * substream first.
  

• */
  

• if (atomic_read(&ss->msg_count)) {

• rc = virtsnd_pcm_hw_params(substream, NULL);
  

• if (rc)
  

• 	return rc;
  

• }
• spin_lock_irqsave(&queue->lock, flags);
• ss->msg_last_enqueued = -1;
• spin_unlock_irqrestore(&queue->lock, flags);
• /*

• * Since I/O messages are asynchronous, they can be completed
  

• * when the runtime structure no longer exists. Since each
  

• * completion implies incrementing the hw_ptr, we cache all the
  

• * current values needed to compute the new hw_ptr value.
  

• */
  

• ss->frame_bytes = substream->runtime->frame_bits >> 3;
• ss->period_size = substream->runtime->period_size;
• ss->buffer_size = substream->runtime->buffer_size;
• atomic_set(&ss->hw_ptr, 0);
• atomic_set(&ss->xfer_xrun, 0);
• atomic_set(&ss->msg_count, 0);
• msg = virtsnd_pcm_ctl_msg_alloc(ss, VIRTIO_SND_R_PCM_PREPARE,

• 			GFP_KERNEL);
  

• if (IS_ERR(msg))

• return PTR_ERR(msg);
  

• return virtsnd_ctl_msg_send_sync(ss->snd, msg);

+}

+/**

• • virtsnd_pcm_trigger() - Process command for the PCM substream.
• • @substream: Kernel ALSA substream.
• • @command: Substream command (SNDRV_PCM_TRIGGER_XXX).
• • Depending on the command, the function does the following:
• • 1. enables/disables data transmission,
• • 2. starts/stops the substream on the device side.
• • Context: Atomic context. May take and release the tx/rx queue spinlock.

Really? Cannot .trigger() sleep? E.g. I see mdelay(25) in snd_es18xx_playback1_trigger()

• • Return: 0 on success, -errno on failure.
• */

+static int virtsnd_pcm_trigger(struct snd_pcm_substream *substream, int command) +{

• struct virtio_pcm_substream *ss = snd_pcm_substream_chip(substream);
• struct virtio_snd *snd = ss->snd;
• struct virtio_snd_queue *queue = virtsnd_pcm_queue(ss);
• struct virtio_snd_msg *msg;
• switch (command) {
• case SNDRV_PCM_TRIGGER_START:
• case SNDRV_PCM_TRIGGER_PAUSE_RELEASE: {

• int rc;
  

• spin_lock(&queue->lock);
  

• rc = virtsnd_pcm_msg_send(ss);
  

• spin_unlock(&queue->lock);
  

Maybe it would be good to explain why locking is required here and isn't required in most other locations, where messages are sent?

Thanks Guennadi

• if (rc)
  

• 	return rc;
  

• atomic_set(&ss->xfer_enabled, 1);
  

• msg = virtsnd_pcm_ctl_msg_alloc(ss, VIRTIO_SND_R_PCM_START,
  

• 				GFP_ATOMIC);
  

• if (IS_ERR(msg))
  

• 	return PTR_ERR(msg);
  

• return virtsnd_ctl_msg_send(snd, msg);
  

• }
• case SNDRV_PCM_TRIGGER_STOP:
• case SNDRV_PCM_TRIGGER_PAUSE_PUSH: {

• atomic_set(&ss->xfer_enabled, 0);
  

• msg = virtsnd_pcm_ctl_msg_alloc(ss, VIRTIO_SND_R_PCM_STOP,
  

• 				GFP_ATOMIC);
  

• if (IS_ERR(msg))
  

• 	return PTR_ERR(msg);
  

• return virtsnd_ctl_msg_send(snd, msg);
  

• }
• default: {

• return -EINVAL;
  

• }
• }

+}

+/**

• • virtsnd_pcm_pointer() - Get the current hardware position for the PCM

• •                     substream.
    

• • @substream: Kernel ALSA substream.
• • Context: Atomic context.
• • Return: Hardware position in frames inside [0 ... buffer_size) range.
• */

+static snd_pcm_uframes_t +virtsnd_pcm_pointer(struct snd_pcm_substream *substream) +{

• struct virtio_pcm_substream *ss = snd_pcm_substream_chip(substream);
• if (atomic_read(&ss->xfer_xrun))

• return SNDRV_PCM_POS_XRUN;
  

• return (snd_pcm_uframes_t)atomic_read(&ss->hw_ptr);

+}

+/* PCM substream operators map. */ +const struct snd_pcm_ops virtsnd_pcm_ops = {

• .open = virtsnd_pcm_open,
• .close = virtsnd_pcm_close,
• .ioctl = snd_pcm_lib_ioctl,
• .hw_params = virtsnd_pcm_hw_params,
• .hw_free = virtsnd_pcm_hw_free,
• .prepare = virtsnd_pcm_prepare,
• .trigger = virtsnd_pcm_trigger,
• .pointer = virtsnd_pcm_pointer,

+};

2.30.0

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