Re: [RFC PATCH] ALSA: virtio: use copy and fill_silence callbacks

Re: [RFC PATCH] ALSA: virtio: use copy and fill_silence callbacks

[Michael S. Tsirkin]

On Thu, Oct 12, 2023 at 05:10:50PM +0200, Matias Ezequiel Vara Larsen wrote:
> This commit replaces the mmap mechanism with the copy() and
> fill_silence() callbacks for both capturing and playback for the
> virtio-sound driver. This change is required to prevent the updating of
> the content of a buffer that is already in the available ring.
> 
> The current mechanism splits a dma buffer into descriptors that are
> exposed to the device. This dma buffer is shared with the user
> application. When the device consumes a buffer, the driver moves the
> request from the used ring to available ring.
> 
> The driver exposes the buffer to the device without knowing if the
> content has been updated from the user. The section 2.8.21.1 of the
> virtio spec states that: "The device MAY access the descriptor chains
> the driver created and the memory they refer to immediately". If the
> device picks up buffers from the available ring just after it is
> notified, it happens that the content may be old.
> 
> By providing the copy() callback, the driver first updates the content
> of the buffer, and then, exposes the buffer to the device by enqueuing
> it in the available ring. Thus, device always picks up a buffer that is
> updated.
> 
> For capturing, the driver starts by exposing all the available buffers
> to device. After device updates the content of a buffer, it enqueues it
> in the used ring. It is only after the copy() for capturing is issued
> that the driver re-enqueues the buffer in the available ring.
> 
> Note that the copy() function assumes that user is always writing a
> period. Testing shows that this is true but I may be wrong. This RFC
> aims at clarifying this.
> 
> Signed-off-by: Matias Ezequiel Vara Larsen <mvaralar@redhat.com>


Thank you for working on this!

> ---
>  sound/virtio/virtio_pcm.c     | 11 ++--
>  sound/virtio/virtio_pcm.h     |  9 +++-
>  sound/virtio/virtio_pcm_msg.c | 50 ++++++++++++++++---
>  sound/virtio/virtio_pcm_ops.c | 94 +++++++++++++++++++++++++++++++----
>  4 files changed, 137 insertions(+), 27 deletions(-)
> 
> diff --git a/sound/virtio/virtio_pcm.c b/sound/virtio/virtio_pcm.c
> index c10d91fff2fb..bfe982952303 100644
> --- a/sound/virtio/virtio_pcm.c
> +++ b/sound/virtio/virtio_pcm.c
> @@ -104,8 +104,6 @@ static int virtsnd_pcm_build_hw(struct virtio_pcm_substream *vss,
>  	 * only message-based transport.
>  	 */
>  	vss->hw.info =
> -		SNDRV_PCM_INFO_MMAP |
> -		SNDRV_PCM_INFO_MMAP_VALID |
>  		SNDRV_PCM_INFO_BATCH |
>  		SNDRV_PCM_INFO_BLOCK_TRANSFER |
>  		SNDRV_PCM_INFO_INTERLEAVED |
> @@ -471,12 +469,11 @@ int virtsnd_pcm_build_devs(struct virtio_snd *snd)
>  			for (kss = ks->substream; kss; kss = kss->next)
>  				vs->substreams[kss->number]->substream = kss;
>  
> -			snd_pcm_set_ops(vpcm->pcm, i, &virtsnd_pcm_ops);
> +			if (i == SNDRV_PCM_STREAM_CAPTURE)
> +				snd_pcm_set_ops(vpcm->pcm, i, &virtsnd_pcm_capture_ops);
> +			else
> +				snd_pcm_set_ops(vpcm->pcm, i, &virtsnd_pcm_playback_ops);
>  		}
> -
> -		snd_pcm_set_managed_buffer_all(vpcm->pcm,
> -					       SNDRV_DMA_TYPE_VMALLOC, NULL,
> -					       0, 0);
>  	}
>  
>  	return 0;
> diff --git a/sound/virtio/virtio_pcm.h b/sound/virtio/virtio_pcm.h
> index 062eb8e8f2cf..1c1106ec971f 100644
> --- a/sound/virtio/virtio_pcm.h
> +++ b/sound/virtio/virtio_pcm.h
> @@ -50,6 +50,8 @@ struct virtio_pcm_substream {
>  	struct work_struct elapsed_period;
>  	spinlock_t lock;
>  	size_t buffer_bytes;
> +	u8 *buffer;
> +	size_t buffer_sz;
>  	size_t hw_ptr;
>  	bool xfer_enabled;
>  	bool xfer_xrun;
> @@ -90,7 +92,8 @@ struct virtio_pcm {
>  	struct virtio_pcm_stream streams[SNDRV_PCM_STREAM_LAST + 1];
>  };
>  
> -extern const struct snd_pcm_ops virtsnd_pcm_ops;
> +extern const struct snd_pcm_ops virtsnd_pcm_playback_ops;
> +extern const struct snd_pcm_ops virtsnd_pcm_capture_ops;
>  
>  int virtsnd_pcm_validate(struct virtio_device *vdev);
>  
> @@ -117,7 +120,9 @@ int virtsnd_pcm_msg_alloc(struct virtio_pcm_substream *vss,
>  
>  void virtsnd_pcm_msg_free(struct virtio_pcm_substream *vss);
>  
> -int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss);
> +int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss, bool single);
> +
> +int virtsnd_pcm_msg_send_locked(struct virtio_pcm_substream *vss, bool single);
>  
>  unsigned int virtsnd_pcm_msg_pending_num(struct virtio_pcm_substream *vss);
>  
> diff --git a/sound/virtio/virtio_pcm_msg.c b/sound/virtio/virtio_pcm_msg.c
> index aca2dc1989ba..9a5f9814cb62 100644
> --- a/sound/virtio/virtio_pcm_msg.c
> +++ b/sound/virtio/virtio_pcm_msg.c
> @@ -132,7 +132,6 @@ static void virtsnd_pcm_sg_from(struct scatterlist *sgs, int nsgs, u8 *data,
>  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;
>  
>  	vss->msgs = kcalloc(periods, sizeof(*vss->msgs), GFP_KERNEL);
> @@ -142,7 +141,7 @@ int virtsnd_pcm_msg_alloc(struct virtio_pcm_substream *vss,
>  	vss->nmsgs = periods;
>  
>  	for (i = 0; i < periods; ++i) {
> -		u8 *data = runtime->dma_area + period_bytes * i;
> +		u8 *data = vss->buffer + period_bytes * i;
>  		int sg_num = virtsnd_pcm_sg_num(data, period_bytes);
>  		struct virtio_pcm_msg *msg;
>  
> @@ -186,10 +185,12 @@ void virtsnd_pcm_msg_free(struct virtio_pcm_substream *vss)
>  /**
>   * virtsnd_pcm_msg_send() - Send asynchronous I/O messages.
>   * @vss: VirtIO PCM substream.
> + * @single: true to enqueue a single message, false to enqueue all of them.
>   *
>   * 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:
> + * function is called, first non-enqueued message is added to the virtqueue.
> + * When single is True, only the first message is enqueued. When False, all the
> + * available messages are enqueued.  The function keeps track of two values:
>   *
>   *   msg_last_enqueued = index of the last enqueued message,
>   *   msg_count = # of pending messages in the virtqueue.
> @@ -198,7 +199,7 @@ void virtsnd_pcm_msg_free(struct virtio_pcm_substream *vss)
>   *          spinlocks to be held by caller.
>   * Return: 0 on success, -errno on failure.
>   */
> -int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss)
> +int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss, bool single)
>  {
>  	struct snd_pcm_runtime *runtime = vss->substream->runtime;
>  	struct virtio_snd *snd = vss->snd;
> @@ -211,6 +212,13 @@ int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss)
>  	i = (vss->msg_last_enqueued + 1) % runtime->periods;
>  	n = runtime->periods - vss->msg_count;
>  
> +	if (single) {
> +		if (n < 1)
> +			return -EFAULT;
> +
> +		n = 1;
> +	}
> +
>  	for (; n; --n, i = (i + 1) % runtime->periods) {
>  		struct virtio_pcm_msg *msg = vss->msgs[i];
>  		struct scatterlist *psgs[] = {
> @@ -250,6 +258,36 @@ int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss)
>  	return 0;
>  }
>  
> +/**
> + * virtsnd_pcm_msg_send_locked() - Send asynchronous I/O messages.
> + * @vss: VirtIO PCM substream.
> + * @single: true to enqueue a single message, false to enqueue all of them.
> + *
> + * This function holds the tx/rx queue and the VirtIO substream spinlocks
> + * before calling virtsnd_pcm_msg_send(). This is a wrapper function to ease
> + * the invocation of virtsnd_pcm_msg_send().
> + *
> + * Context: Any context.
> + * Return: 0 on success, -errno on failure.
> + */
> +
> +int virtsnd_pcm_msg_send_locked(struct virtio_pcm_substream *vss, bool single)
> +{
> +	struct virtio_snd_queue *queue;
> +	int rc;
> +	unsigned long flags;
> +
> +	queue = virtsnd_pcm_queue(vss);
> +
> +	spin_lock_irqsave(&queue->lock, flags);
> +	spin_lock(&vss->lock);
> +	rc = virtsnd_pcm_msg_send(vss, single);
> +	spin_unlock(&vss->lock);
> +	spin_unlock_irqrestore(&queue->lock, flags);
> +
> +	return rc;
> +}
> +
>  /**
>   * virtsnd_pcm_msg_pending_num() - Returns the number of pending I/O messages.
>   * @vss: VirtIO substream.
> @@ -320,8 +358,6 @@ static void virtsnd_pcm_msg_complete(struct virtio_pcm_msg *msg,
>  					le32_to_cpu(msg->status.latency_bytes));
>  
>  		schedule_work(&vss->elapsed_period);
> -
> -		virtsnd_pcm_msg_send(vss);
>  	} else if (!vss->msg_count) {
>  		wake_up_all(&vss->msg_empty);
>  	}
> diff --git a/sound/virtio/virtio_pcm_ops.c b/sound/virtio/virtio_pcm_ops.c
> index f8bfb87624be..a208439dbff8 100644
> --- a/sound/virtio/virtio_pcm_ops.c
> +++ b/sound/virtio/virtio_pcm_ops.c
> @@ -238,6 +238,11 @@ static int virtsnd_pcm_hw_params(struct snd_pcm_substream *substream,
>  	 */
>  	virtsnd_pcm_msg_free(vss);
>  
> +	vss->buffer_sz = params_buffer_bytes(hw_params);
> +	vss->buffer = alloc_pages_exact(vss->buffer_sz, GFP_KERNEL);
> +	if (!vss->buffer)
> +		return -ENOMEM;
> +
>  	return virtsnd_pcm_msg_alloc(vss, params_periods(hw_params),
>  				     params_period_bytes(hw_params));
>  }
> @@ -257,6 +262,11 @@ static int virtsnd_pcm_hw_free(struct snd_pcm_substream *substream)
>  	if (!virtsnd_pcm_msg_pending_num(vss))
>  		virtsnd_pcm_msg_free(vss);
>  
> +	if (vss->buffer) {
> +		free_pages_exact(vss->buffer, vss->buffer_sz);
> +		vss->buffer = NULL;
> +	}
> +
>  	return 0;
>  }
>  
> @@ -331,15 +341,18 @@ static int virtsnd_pcm_trigger(struct snd_pcm_substream *substream, int command)
>  	case SNDRV_PCM_TRIGGER_PAUSE_RELEASE:
>  		queue = virtsnd_pcm_queue(vss);
>  
> -		spin_lock_irqsave(&queue->lock, flags);
> -		spin_lock(&vss->lock);
> -		rc = virtsnd_pcm_msg_send(vss);
> -		if (!rc)
> -			vss->xfer_enabled = true;
> -		spin_unlock(&vss->lock);
> -		spin_unlock_irqrestore(&queue->lock, flags);
> -		if (rc)
> -			return rc;
> +		// The buffers should be exposed first during capturing so that
> +		// the device can consume them. Capturing cannot begin
> +		// otherwise.
> +		if (vss->direction == SNDRV_PCM_STREAM_CAPTURE) {
> +			rc = virtsnd_pcm_msg_send_locked(vss, false);
> +			if (rc)
> +				return rc;
> +		}
> +
> +		spin_lock_irqsave(&vss->lock, flags);
> +		vss->xfer_enabled = true;
> +		spin_unlock_irqrestore(&vss->lock, flags);
>  
>  		msg = virtsnd_pcm_ctl_msg_alloc(vss, VIRTIO_SND_R_PCM_START,
>  						GFP_KERNEL);
> @@ -450,8 +463,66 @@ virtsnd_pcm_pointer(struct snd_pcm_substream *substream)
>  	return hw_ptr;
>  }
>  
> -/* PCM substream operators map. */
> -const struct snd_pcm_ops virtsnd_pcm_ops = {
> +static int virtsnd_pcm_pb_copy(struct snd_pcm_substream *substream,
> +			       int channel, unsigned long pos, struct iov_iter
> +			       *src, unsigned long count)
> +{
> +	struct virtio_pcm_substream *vss = snd_pcm_substream_chip(substream);
> +
> +	if (unlikely(pos + count > vss->buffer_sz))
> +		return -EINVAL;
> +
> +	if (copy_from_iter(vss->buffer + pos, count, src) != count)
> +		return -EFAULT;
> +
> +	return virtsnd_pcm_msg_send_locked(vss, true);
> +}
> +
> +static int virtsnd_pcm_cap_copy(struct snd_pcm_substream *substream,
> +				int channel, unsigned long pos, struct iov_iter
> +				*dst, unsigned long count)
> +{
> +	struct virtio_pcm_substream *vss = snd_pcm_substream_chip(substream);
> +
> +	if (unlikely(pos + count > vss->buffer_sz))
> +		return -EINVAL;
> +
> +	if (copy_to_iter(vss->buffer + pos, count, dst) != count)
> +		return -EFAULT;
> +
> +	return virtsnd_pcm_msg_send_locked(vss, true);
> +}
> +
> +static int virtsnd_pcm_pb_silence(struct snd_pcm_substream *substream, int channel,
> +				  unsigned long pos, unsigned long count)
> +{
> +	struct virtio_pcm_substream *vss = snd_pcm_substream_chip(substream);
> +
> +	if (unlikely(pos + count > vss->buffer_sz))
> +		return -EINVAL;
> +
> +	memset(vss->buffer + pos, 0, count);
> +
> +	return virtsnd_pcm_msg_send_locked(vss, true);
> +}
> +
> +/* PCM substream operators map for playback. */
> +const struct snd_pcm_ops virtsnd_pcm_playback_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,
> +	.sync_stop = virtsnd_pcm_sync_stop,
> +	.pointer = virtsnd_pcm_pointer,
> +	.copy = virtsnd_pcm_pb_copy,
> +	.fill_silence = virtsnd_pcm_pb_silence,
> +};
> +
> +/* PCM substream operators map for capturing. */
> +const struct snd_pcm_ops virtsnd_pcm_capture_ops = {
>  	.open = virtsnd_pcm_open,
>  	.close = virtsnd_pcm_close,
>  	.ioctl = snd_pcm_lib_ioctl,
> @@ -461,4 +532,5 @@ const struct snd_pcm_ops virtsnd_pcm_ops = {
>  	.trigger = virtsnd_pcm_trigger,
>  	.sync_stop = virtsnd_pcm_sync_stop,
>  	.pointer = virtsnd_pcm_pointer,
> +	.copy = virtsnd_pcm_cap_copy,
>  };
> 
> base-commit: 8a749fd1a8720d4619c91c8b6e7528c0a355c0aa
> -- 
> 2.41.0

Re: [RFC PATCH] ALSA: virtio: use copy and fill_silence callbacks

[Stefano Garzarella]

On Thu, Oct 12, 2023 at 11:16:54AM -0400, Michael S. Tsirkin wrote:
>On Thu, Oct 12, 2023 at 05:10:50PM +0200, Matias Ezequiel Vara Larsen wrote:
>> This commit replaces the mmap mechanism with the copy() and
>> fill_silence() callbacks for both capturing and playback for the
>> virtio-sound driver. This change is required to prevent the updating of
>> the content of a buffer that is already in the available ring.
>>
>> The current mechanism splits a dma buffer into descriptors that are
>> exposed to the device. This dma buffer is shared with the user
>> application. When the device consumes a buffer, the driver moves the
>> request from the used ring to available ring.
>>
>> The driver exposes the buffer to the device without knowing if the
>> content has been updated from the user. The section 2.8.21.1 of the
>> virtio spec states that: "The device MAY access the descriptor chains
>> the driver created and the memory they refer to immediately". If the
>> device picks up buffers from the available ring just after it is
>> notified, it happens that the content may be old.
>>
>> By providing the copy() callback, the driver first updates the content
>> of the buffer, and then, exposes the buffer to the device by enqueuing
>> it in the available ring. Thus, device always picks up a buffer that is
>> updated.
>>
>> For capturing, the driver starts by exposing all the available buffers
>> to device. After device updates the content of a buffer, it enqueues it
>> in the used ring. It is only after the copy() for capturing is issued
>> that the driver re-enqueues the buffer in the available ring.
>>
>> Note that the copy() function assumes that user is always writing a
>> period. Testing shows that this is true but I may be wrong. This RFC
>> aims at clarifying this.
>>
>> Signed-off-by: Matias Ezequiel Vara Larsen <mvaralar@redhat.com>
>
>
>Thank you for working on this!

Yep, +1!

@Michael do you think we should cc stable and add a Fixes tag since
the driver is not following the virtio spec?

Or it is too risky?

IIUC snd_pcm_ops is changed a bit from previous versions, so we may have
to adapt the patch for stable branches.

Stefano

>
>> ---
>>  sound/virtio/virtio_pcm.c     | 11 ++--
>>  sound/virtio/virtio_pcm.h     |  9 +++-
>>  sound/virtio/virtio_pcm_msg.c | 50 ++++++++++++++++---
>>  sound/virtio/virtio_pcm_ops.c | 94 +++++++++++++++++++++++++++++++----
>>  4 files changed, 137 insertions(+), 27 deletions(-)
>>
>> diff --git a/sound/virtio/virtio_pcm.c b/sound/virtio/virtio_pcm.c
>> index c10d91fff2fb..bfe982952303 100644
>> --- a/sound/virtio/virtio_pcm.c
>> +++ b/sound/virtio/virtio_pcm.c
>> @@ -104,8 +104,6 @@ static int virtsnd_pcm_build_hw(struct virtio_pcm_substream *vss,
>>  	 * only message-based transport.
>>  	 */
>>  	vss->hw.info =
>> -		SNDRV_PCM_INFO_MMAP |
>> -		SNDRV_PCM_INFO_MMAP_VALID |
>>  		SNDRV_PCM_INFO_BATCH |
>>  		SNDRV_PCM_INFO_BLOCK_TRANSFER |
>>  		SNDRV_PCM_INFO_INTERLEAVED |
>> @@ -471,12 +469,11 @@ int virtsnd_pcm_build_devs(struct virtio_snd *snd)
>>  			for (kss = ks->substream; kss; kss = kss->next)
>>  				vs->substreams[kss->number]->substream = kss;
>>
>> -			snd_pcm_set_ops(vpcm->pcm, i, &virtsnd_pcm_ops);
>> +			if (i == SNDRV_PCM_STREAM_CAPTURE)
>> +				snd_pcm_set_ops(vpcm->pcm, i, &virtsnd_pcm_capture_ops);
>> +			else
>> +				snd_pcm_set_ops(vpcm->pcm, i, &virtsnd_pcm_playback_ops);
>>  		}
>> -
>> -		snd_pcm_set_managed_buffer_all(vpcm->pcm,
>> -					       SNDRV_DMA_TYPE_VMALLOC, NULL,
>> -					       0, 0);
>>  	}
>>
>>  	return 0;
>> diff --git a/sound/virtio/virtio_pcm.h b/sound/virtio/virtio_pcm.h
>> index 062eb8e8f2cf..1c1106ec971f 100644
>> --- a/sound/virtio/virtio_pcm.h
>> +++ b/sound/virtio/virtio_pcm.h
>> @@ -50,6 +50,8 @@ struct virtio_pcm_substream {
>>  	struct work_struct elapsed_period;
>>  	spinlock_t lock;
>>  	size_t buffer_bytes;
>> +	u8 *buffer;
>> +	size_t buffer_sz;
>>  	size_t hw_ptr;
>>  	bool xfer_enabled;
>>  	bool xfer_xrun;
>> @@ -90,7 +92,8 @@ struct virtio_pcm {
>>  	struct virtio_pcm_stream streams[SNDRV_PCM_STREAM_LAST + 1];
>>  };
>>
>> -extern const struct snd_pcm_ops virtsnd_pcm_ops;
>> +extern const struct snd_pcm_ops virtsnd_pcm_playback_ops;
>> +extern const struct snd_pcm_ops virtsnd_pcm_capture_ops;
>>
>>  int virtsnd_pcm_validate(struct virtio_device *vdev);
>>
>> @@ -117,7 +120,9 @@ int virtsnd_pcm_msg_alloc(struct virtio_pcm_substream *vss,
>>
>>  void virtsnd_pcm_msg_free(struct virtio_pcm_substream *vss);
>>
>> -int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss);
>> +int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss, bool single);
>> +
>> +int virtsnd_pcm_msg_send_locked(struct virtio_pcm_substream *vss, bool single);
>>
>>  unsigned int virtsnd_pcm_msg_pending_num(struct virtio_pcm_substream *vss);
>>
>> diff --git a/sound/virtio/virtio_pcm_msg.c b/sound/virtio/virtio_pcm_msg.c
>> index aca2dc1989ba..9a5f9814cb62 100644
>> --- a/sound/virtio/virtio_pcm_msg.c
>> +++ b/sound/virtio/virtio_pcm_msg.c
>> @@ -132,7 +132,6 @@ static void virtsnd_pcm_sg_from(struct scatterlist *sgs, int nsgs, u8 *data,
>>  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;
>>
>>  	vss->msgs = kcalloc(periods, sizeof(*vss->msgs), GFP_KERNEL);
>> @@ -142,7 +141,7 @@ int virtsnd_pcm_msg_alloc(struct virtio_pcm_substream *vss,
>>  	vss->nmsgs = periods;
>>
>>  	for (i = 0; i < periods; ++i) {
>> -		u8 *data = runtime->dma_area + period_bytes * i;
>> +		u8 *data = vss->buffer + period_bytes * i;
>>  		int sg_num = virtsnd_pcm_sg_num(data, period_bytes);
>>  		struct virtio_pcm_msg *msg;
>>
>> @@ -186,10 +185,12 @@ void virtsnd_pcm_msg_free(struct virtio_pcm_substream *vss)
>>  /**
>>   * virtsnd_pcm_msg_send() - Send asynchronous I/O messages.
>>   * @vss: VirtIO PCM substream.
>> + * @single: true to enqueue a single message, false to enqueue all of them.
>>   *
>>   * 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:
>> + * function is called, first non-enqueued message is added to the virtqueue.
>> + * When single is True, only the first message is enqueued. When False, all the
>> + * available messages are enqueued.  The function keeps track of two values:
>>   *
>>   *   msg_last_enqueued = index of the last enqueued message,
>>   *   msg_count = # of pending messages in the virtqueue.
>> @@ -198,7 +199,7 @@ void virtsnd_pcm_msg_free(struct virtio_pcm_substream *vss)
>>   *          spinlocks to be held by caller.
>>   * Return: 0 on success, -errno on failure.
>>   */
>> -int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss)
>> +int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss, bool single)
>>  {
>>  	struct snd_pcm_runtime *runtime = vss->substream->runtime;
>>  	struct virtio_snd *snd = vss->snd;
>> @@ -211,6 +212,13 @@ int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss)
>>  	i = (vss->msg_last_enqueued + 1) % runtime->periods;
>>  	n = runtime->periods - vss->msg_count;
>>
>> +	if (single) {
>> +		if (n < 1)
>> +			return -EFAULT;
>> +
>> +		n = 1;
>> +	}
>> +
>>  	for (; n; --n, i = (i + 1) % runtime->periods) {
>>  		struct virtio_pcm_msg *msg = vss->msgs[i];
>>  		struct scatterlist *psgs[] = {
>> @@ -250,6 +258,36 @@ int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss)
>>  	return 0;
>>  }
>>
>> +/**
>> + * virtsnd_pcm_msg_send_locked() - Send asynchronous I/O messages.
>> + * @vss: VirtIO PCM substream.
>> + * @single: true to enqueue a single message, false to enqueue all of them.
>> + *
>> + * This function holds the tx/rx queue and the VirtIO substream spinlocks
>> + * before calling virtsnd_pcm_msg_send(). This is a wrapper function to ease
>> + * the invocation of virtsnd_pcm_msg_send().
>> + *
>> + * Context: Any context.
>> + * Return: 0 on success, -errno on failure.
>> + */
>> +
>> +int virtsnd_pcm_msg_send_locked(struct virtio_pcm_substream *vss, bool single)
>> +{
>> +	struct virtio_snd_queue *queue;
>> +	int rc;
>> +	unsigned long flags;
>> +
>> +	queue = virtsnd_pcm_queue(vss);
>> +
>> +	spin_lock_irqsave(&queue->lock, flags);
>> +	spin_lock(&vss->lock);
>> +	rc = virtsnd_pcm_msg_send(vss, single);
>> +	spin_unlock(&vss->lock);
>> +	spin_unlock_irqrestore(&queue->lock, flags);
>> +
>> +	return rc;
>> +}
>> +
>>  /**
>>   * virtsnd_pcm_msg_pending_num() - Returns the number of pending I/O messages.
>>   * @vss: VirtIO substream.
>> @@ -320,8 +358,6 @@ static void virtsnd_pcm_msg_complete(struct virtio_pcm_msg *msg,
>>  					le32_to_cpu(msg->status.latency_bytes));
>>
>>  		schedule_work(&vss->elapsed_period);
>> -
>> -		virtsnd_pcm_msg_send(vss);
>>  	} else if (!vss->msg_count) {
>>  		wake_up_all(&vss->msg_empty);
>>  	}
>> diff --git a/sound/virtio/virtio_pcm_ops.c b/sound/virtio/virtio_pcm_ops.c
>> index f8bfb87624be..a208439dbff8 100644
>> --- a/sound/virtio/virtio_pcm_ops.c
>> +++ b/sound/virtio/virtio_pcm_ops.c
>> @@ -238,6 +238,11 @@ static int virtsnd_pcm_hw_params(struct snd_pcm_substream *substream,
>>  	 */
>>  	virtsnd_pcm_msg_free(vss);
>>
>> +	vss->buffer_sz = params_buffer_bytes(hw_params);
>> +	vss->buffer = alloc_pages_exact(vss->buffer_sz, GFP_KERNEL);
>> +	if (!vss->buffer)
>> +		return -ENOMEM;
>> +
>>  	return virtsnd_pcm_msg_alloc(vss, params_periods(hw_params),
>>  				     params_period_bytes(hw_params));
>>  }
>> @@ -257,6 +262,11 @@ static int virtsnd_pcm_hw_free(struct snd_pcm_substream *substream)
>>  	if (!virtsnd_pcm_msg_pending_num(vss))
>>  		virtsnd_pcm_msg_free(vss);
>>
>> +	if (vss->buffer) {
>> +		free_pages_exact(vss->buffer, vss->buffer_sz);
>> +		vss->buffer = NULL;
>> +	}
>> +
>>  	return 0;
>>  }
>>
>> @@ -331,15 +341,18 @@ static int virtsnd_pcm_trigger(struct snd_pcm_substream *substream, int command)
>>  	case SNDRV_PCM_TRIGGER_PAUSE_RELEASE:
>>  		queue = virtsnd_pcm_queue(vss);
>>
>> -		spin_lock_irqsave(&queue->lock, flags);
>> -		spin_lock(&vss->lock);
>> -		rc = virtsnd_pcm_msg_send(vss);
>> -		if (!rc)
>> -			vss->xfer_enabled = true;
>> -		spin_unlock(&vss->lock);
>> -		spin_unlock_irqrestore(&queue->lock, flags);
>> -		if (rc)
>> -			return rc;
>> +		// The buffers should be exposed first during capturing so that
>> +		// the device can consume them. Capturing cannot begin
>> +		// otherwise.
>> +		if (vss->direction == SNDRV_PCM_STREAM_CAPTURE) {
>> +			rc = virtsnd_pcm_msg_send_locked(vss, false);
>> +			if (rc)
>> +				return rc;
>> +		}
>> +
>> +		spin_lock_irqsave(&vss->lock, flags);
>> +		vss->xfer_enabled = true;
>> +		spin_unlock_irqrestore(&vss->lock, flags);
>>
>>  		msg = virtsnd_pcm_ctl_msg_alloc(vss, VIRTIO_SND_R_PCM_START,
>>  						GFP_KERNEL);
>> @@ -450,8 +463,66 @@ virtsnd_pcm_pointer(struct snd_pcm_substream *substream)
>>  	return hw_ptr;
>>  }
>>
>> -/* PCM substream operators map. */
>> -const struct snd_pcm_ops virtsnd_pcm_ops = {
>> +static int virtsnd_pcm_pb_copy(struct snd_pcm_substream *substream,
>> +			       int channel, unsigned long pos, struct iov_iter
>> +			       *src, unsigned long count)
>> +{
>> +	struct virtio_pcm_substream *vss = snd_pcm_substream_chip(substream);
>> +
>> +	if (unlikely(pos + count > vss->buffer_sz))
>> +		return -EINVAL;
>> +
>> +	if (copy_from_iter(vss->buffer + pos, count, src) != count)
>> +		return -EFAULT;
>> +
>> +	return virtsnd_pcm_msg_send_locked(vss, true);
>> +}
>> +
>> +static int virtsnd_pcm_cap_copy(struct snd_pcm_substream *substream,
>> +				int channel, unsigned long pos, struct iov_iter
>> +				*dst, unsigned long count)
>> +{
>> +	struct virtio_pcm_substream *vss = snd_pcm_substream_chip(substream);
>> +
>> +	if (unlikely(pos + count > vss->buffer_sz))
>> +		return -EINVAL;
>> +
>> +	if (copy_to_iter(vss->buffer + pos, count, dst) != count)
>> +		return -EFAULT;
>> +
>> +	return virtsnd_pcm_msg_send_locked(vss, true);
>> +}
>> +
>> +static int virtsnd_pcm_pb_silence(struct snd_pcm_substream *substream, int channel,
>> +				  unsigned long pos, unsigned long count)
>> +{
>> +	struct virtio_pcm_substream *vss = snd_pcm_substream_chip(substream);
>> +
>> +	if (unlikely(pos + count > vss->buffer_sz))
>> +		return -EINVAL;
>> +
>> +	memset(vss->buffer + pos, 0, count);
>> +
>> +	return virtsnd_pcm_msg_send_locked(vss, true);
>> +}
>> +
>> +/* PCM substream operators map for playback. */
>> +const struct snd_pcm_ops virtsnd_pcm_playback_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,
>> +	.sync_stop = virtsnd_pcm_sync_stop,
>> +	.pointer = virtsnd_pcm_pointer,
>> +	.copy = virtsnd_pcm_pb_copy,
>> +	.fill_silence = virtsnd_pcm_pb_silence,
>> +};
>> +
>> +/* PCM substream operators map for capturing. */
>> +const struct snd_pcm_ops virtsnd_pcm_capture_ops = {
>>  	.open = virtsnd_pcm_open,
>>  	.close = virtsnd_pcm_close,
>>  	.ioctl = snd_pcm_lib_ioctl,
>> @@ -461,4 +532,5 @@ const struct snd_pcm_ops virtsnd_pcm_ops = {
>>  	.trigger = virtsnd_pcm_trigger,
>>  	.sync_stop = virtsnd_pcm_sync_stop,
>>  	.pointer = virtsnd_pcm_pointer,
>> +	.copy = virtsnd_pcm_cap_copy,
>>  };
>>
>> base-commit: 8a749fd1a8720d4619c91c8b6e7528c0a355c0aa
>> --
>> 2.41.0
>

Re: [RFC PATCH] ALSA: virtio: use copy and fill_silence callbacks

[Stefan Hajnoczi]

[-- Attachment #1: Type: text/plain, Size: 13264 bytes --]

On Thu, Oct 12, 2023 at 05:10:50PM +0200, Matias Ezequiel Vara Larsen wrote:
> This commit replaces the mmap mechanism with the copy() and
> fill_silence() callbacks for both capturing and playback for the
> virtio-sound driver. This change is required to prevent the updating of
> the content of a buffer that is already in the available ring.
> 
> The current mechanism splits a dma buffer into descriptors that are
> exposed to the device. This dma buffer is shared with the user
> application. When the device consumes a buffer, the driver moves the
> request from the used ring to available ring.
> 
> The driver exposes the buffer to the device without knowing if the
> content has been updated from the user. The section 2.8.21.1 of the
> virtio spec states that: "The device MAY access the descriptor chains
> the driver created and the memory they refer to immediately". If the
> device picks up buffers from the available ring just after it is
> notified, it happens that the content may be old.
> 
> By providing the copy() callback, the driver first updates the content
> of the buffer, and then, exposes the buffer to the device by enqueuing
> it in the available ring. Thus, device always picks up a buffer that is
> updated.
> 
> For capturing, the driver starts by exposing all the available buffers
> to device. After device updates the content of a buffer, it enqueues it
> in the used ring. It is only after the copy() for capturing is issued
> that the driver re-enqueues the buffer in the available ring.
> 
> Note that the copy() function assumes that user is always writing a
> period. Testing shows that this is true but I may be wrong. This RFC
> aims at clarifying this.

This sounds like an ALSA driver API question.

Jaroslav and Takashi: Any thoughts?

Stefan

> 
> Signed-off-by: Matias Ezequiel Vara Larsen <mvaralar@redhat.com>
> ---
>  sound/virtio/virtio_pcm.c     | 11 ++--
>  sound/virtio/virtio_pcm.h     |  9 +++-
>  sound/virtio/virtio_pcm_msg.c | 50 ++++++++++++++++---
>  sound/virtio/virtio_pcm_ops.c | 94 +++++++++++++++++++++++++++++++----
>  4 files changed, 137 insertions(+), 27 deletions(-)
> 
> diff --git a/sound/virtio/virtio_pcm.c b/sound/virtio/virtio_pcm.c
> index c10d91fff2fb..bfe982952303 100644
> --- a/sound/virtio/virtio_pcm.c
> +++ b/sound/virtio/virtio_pcm.c
> @@ -104,8 +104,6 @@ static int virtsnd_pcm_build_hw(struct virtio_pcm_substream *vss,
>  	 * only message-based transport.
>  	 */
>  	vss->hw.info =
> -		SNDRV_PCM_INFO_MMAP |
> -		SNDRV_PCM_INFO_MMAP_VALID |
>  		SNDRV_PCM_INFO_BATCH |
>  		SNDRV_PCM_INFO_BLOCK_TRANSFER |
>  		SNDRV_PCM_INFO_INTERLEAVED |
> @@ -471,12 +469,11 @@ int virtsnd_pcm_build_devs(struct virtio_snd *snd)
>  			for (kss = ks->substream; kss; kss = kss->next)
>  				vs->substreams[kss->number]->substream = kss;
>  
> -			snd_pcm_set_ops(vpcm->pcm, i, &virtsnd_pcm_ops);
> +			if (i == SNDRV_PCM_STREAM_CAPTURE)
> +				snd_pcm_set_ops(vpcm->pcm, i, &virtsnd_pcm_capture_ops);
> +			else
> +				snd_pcm_set_ops(vpcm->pcm, i, &virtsnd_pcm_playback_ops);
>  		}
> -
> -		snd_pcm_set_managed_buffer_all(vpcm->pcm,
> -					       SNDRV_DMA_TYPE_VMALLOC, NULL,
> -					       0, 0);
>  	}
>  
>  	return 0;
> diff --git a/sound/virtio/virtio_pcm.h b/sound/virtio/virtio_pcm.h
> index 062eb8e8f2cf..1c1106ec971f 100644
> --- a/sound/virtio/virtio_pcm.h
> +++ b/sound/virtio/virtio_pcm.h
> @@ -50,6 +50,8 @@ struct virtio_pcm_substream {
>  	struct work_struct elapsed_period;
>  	spinlock_t lock;
>  	size_t buffer_bytes;
> +	u8 *buffer;
> +	size_t buffer_sz;
>  	size_t hw_ptr;
>  	bool xfer_enabled;
>  	bool xfer_xrun;
> @@ -90,7 +92,8 @@ struct virtio_pcm {
>  	struct virtio_pcm_stream streams[SNDRV_PCM_STREAM_LAST + 1];
>  };
>  
> -extern const struct snd_pcm_ops virtsnd_pcm_ops;
> +extern const struct snd_pcm_ops virtsnd_pcm_playback_ops;
> +extern const struct snd_pcm_ops virtsnd_pcm_capture_ops;
>  
>  int virtsnd_pcm_validate(struct virtio_device *vdev);
>  
> @@ -117,7 +120,9 @@ int virtsnd_pcm_msg_alloc(struct virtio_pcm_substream *vss,
>  
>  void virtsnd_pcm_msg_free(struct virtio_pcm_substream *vss);
>  
> -int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss);
> +int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss, bool single);
> +
> +int virtsnd_pcm_msg_send_locked(struct virtio_pcm_substream *vss, bool single);
>  
>  unsigned int virtsnd_pcm_msg_pending_num(struct virtio_pcm_substream *vss);
>  
> diff --git a/sound/virtio/virtio_pcm_msg.c b/sound/virtio/virtio_pcm_msg.c
> index aca2dc1989ba..9a5f9814cb62 100644
> --- a/sound/virtio/virtio_pcm_msg.c
> +++ b/sound/virtio/virtio_pcm_msg.c
> @@ -132,7 +132,6 @@ static void virtsnd_pcm_sg_from(struct scatterlist *sgs, int nsgs, u8 *data,
>  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;
>  
>  	vss->msgs = kcalloc(periods, sizeof(*vss->msgs), GFP_KERNEL);
> @@ -142,7 +141,7 @@ int virtsnd_pcm_msg_alloc(struct virtio_pcm_substream *vss,
>  	vss->nmsgs = periods;
>  
>  	for (i = 0; i < periods; ++i) {
> -		u8 *data = runtime->dma_area + period_bytes * i;
> +		u8 *data = vss->buffer + period_bytes * i;
>  		int sg_num = virtsnd_pcm_sg_num(data, period_bytes);
>  		struct virtio_pcm_msg *msg;
>  
> @@ -186,10 +185,12 @@ void virtsnd_pcm_msg_free(struct virtio_pcm_substream *vss)
>  /**
>   * virtsnd_pcm_msg_send() - Send asynchronous I/O messages.
>   * @vss: VirtIO PCM substream.
> + * @single: true to enqueue a single message, false to enqueue all of them.
>   *
>   * 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:
> + * function is called, first non-enqueued message is added to the virtqueue.
> + * When single is True, only the first message is enqueued. When False, all the
> + * available messages are enqueued.  The function keeps track of two values:
>   *
>   *   msg_last_enqueued = index of the last enqueued message,
>   *   msg_count = # of pending messages in the virtqueue.
> @@ -198,7 +199,7 @@ void virtsnd_pcm_msg_free(struct virtio_pcm_substream *vss)
>   *          spinlocks to be held by caller.
>   * Return: 0 on success, -errno on failure.
>   */
> -int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss)
> +int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss, bool single)
>  {
>  	struct snd_pcm_runtime *runtime = vss->substream->runtime;
>  	struct virtio_snd *snd = vss->snd;
> @@ -211,6 +212,13 @@ int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss)
>  	i = (vss->msg_last_enqueued + 1) % runtime->periods;
>  	n = runtime->periods - vss->msg_count;
>  
> +	if (single) {
> +		if (n < 1)
> +			return -EFAULT;
> +
> +		n = 1;
> +	}
> +
>  	for (; n; --n, i = (i + 1) % runtime->periods) {
>  		struct virtio_pcm_msg *msg = vss->msgs[i];
>  		struct scatterlist *psgs[] = {
> @@ -250,6 +258,36 @@ int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss)
>  	return 0;
>  }
>  
> +/**
> + * virtsnd_pcm_msg_send_locked() - Send asynchronous I/O messages.
> + * @vss: VirtIO PCM substream.
> + * @single: true to enqueue a single message, false to enqueue all of them.
> + *
> + * This function holds the tx/rx queue and the VirtIO substream spinlocks
> + * before calling virtsnd_pcm_msg_send(). This is a wrapper function to ease
> + * the invocation of virtsnd_pcm_msg_send().
> + *
> + * Context: Any context.
> + * Return: 0 on success, -errno on failure.
> + */
> +
> +int virtsnd_pcm_msg_send_locked(struct virtio_pcm_substream *vss, bool single)
> +{
> +	struct virtio_snd_queue *queue;
> +	int rc;
> +	unsigned long flags;
> +
> +	queue = virtsnd_pcm_queue(vss);
> +
> +	spin_lock_irqsave(&queue->lock, flags);
> +	spin_lock(&vss->lock);
> +	rc = virtsnd_pcm_msg_send(vss, single);
> +	spin_unlock(&vss->lock);
> +	spin_unlock_irqrestore(&queue->lock, flags);
> +
> +	return rc;
> +}
> +
>  /**
>   * virtsnd_pcm_msg_pending_num() - Returns the number of pending I/O messages.
>   * @vss: VirtIO substream.
> @@ -320,8 +358,6 @@ static void virtsnd_pcm_msg_complete(struct virtio_pcm_msg *msg,
>  					le32_to_cpu(msg->status.latency_bytes));
>  
>  		schedule_work(&vss->elapsed_period);
> -
> -		virtsnd_pcm_msg_send(vss);
>  	} else if (!vss->msg_count) {
>  		wake_up_all(&vss->msg_empty);
>  	}
> diff --git a/sound/virtio/virtio_pcm_ops.c b/sound/virtio/virtio_pcm_ops.c
> index f8bfb87624be..a208439dbff8 100644
> --- a/sound/virtio/virtio_pcm_ops.c
> +++ b/sound/virtio/virtio_pcm_ops.c
> @@ -238,6 +238,11 @@ static int virtsnd_pcm_hw_params(struct snd_pcm_substream *substream,
>  	 */
>  	virtsnd_pcm_msg_free(vss);
>  
> +	vss->buffer_sz = params_buffer_bytes(hw_params);
> +	vss->buffer = alloc_pages_exact(vss->buffer_sz, GFP_KERNEL);
> +	if (!vss->buffer)
> +		return -ENOMEM;
> +
>  	return virtsnd_pcm_msg_alloc(vss, params_periods(hw_params),
>  				     params_period_bytes(hw_params));
>  }
> @@ -257,6 +262,11 @@ static int virtsnd_pcm_hw_free(struct snd_pcm_substream *substream)
>  	if (!virtsnd_pcm_msg_pending_num(vss))
>  		virtsnd_pcm_msg_free(vss);
>  
> +	if (vss->buffer) {
> +		free_pages_exact(vss->buffer, vss->buffer_sz);
> +		vss->buffer = NULL;
> +	}
> +
>  	return 0;
>  }
>  
> @@ -331,15 +341,18 @@ static int virtsnd_pcm_trigger(struct snd_pcm_substream *substream, int command)
>  	case SNDRV_PCM_TRIGGER_PAUSE_RELEASE:
>  		queue = virtsnd_pcm_queue(vss);
>  
> -		spin_lock_irqsave(&queue->lock, flags);
> -		spin_lock(&vss->lock);
> -		rc = virtsnd_pcm_msg_send(vss);
> -		if (!rc)
> -			vss->xfer_enabled = true;
> -		spin_unlock(&vss->lock);
> -		spin_unlock_irqrestore(&queue->lock, flags);
> -		if (rc)
> -			return rc;
> +		// The buffers should be exposed first during capturing so that
> +		// the device can consume them. Capturing cannot begin
> +		// otherwise.
> +		if (vss->direction == SNDRV_PCM_STREAM_CAPTURE) {
> +			rc = virtsnd_pcm_msg_send_locked(vss, false);
> +			if (rc)
> +				return rc;
> +		}
> +
> +		spin_lock_irqsave(&vss->lock, flags);
> +		vss->xfer_enabled = true;
> +		spin_unlock_irqrestore(&vss->lock, flags);
>  
>  		msg = virtsnd_pcm_ctl_msg_alloc(vss, VIRTIO_SND_R_PCM_START,
>  						GFP_KERNEL);
> @@ -450,8 +463,66 @@ virtsnd_pcm_pointer(struct snd_pcm_substream *substream)
>  	return hw_ptr;
>  }
>  
> -/* PCM substream operators map. */
> -const struct snd_pcm_ops virtsnd_pcm_ops = {
> +static int virtsnd_pcm_pb_copy(struct snd_pcm_substream *substream,
> +			       int channel, unsigned long pos, struct iov_iter
> +			       *src, unsigned long count)
> +{
> +	struct virtio_pcm_substream *vss = snd_pcm_substream_chip(substream);
> +
> +	if (unlikely(pos + count > vss->buffer_sz))
> +		return -EINVAL;
> +
> +	if (copy_from_iter(vss->buffer + pos, count, src) != count)
> +		return -EFAULT;
> +
> +	return virtsnd_pcm_msg_send_locked(vss, true);
> +}
> +
> +static int virtsnd_pcm_cap_copy(struct snd_pcm_substream *substream,
> +				int channel, unsigned long pos, struct iov_iter
> +				*dst, unsigned long count)
> +{
> +	struct virtio_pcm_substream *vss = snd_pcm_substream_chip(substream);
> +
> +	if (unlikely(pos + count > vss->buffer_sz))
> +		return -EINVAL;
> +
> +	if (copy_to_iter(vss->buffer + pos, count, dst) != count)
> +		return -EFAULT;
> +
> +	return virtsnd_pcm_msg_send_locked(vss, true);
> +}
> +
> +static int virtsnd_pcm_pb_silence(struct snd_pcm_substream *substream, int channel,
> +				  unsigned long pos, unsigned long count)
> +{
> +	struct virtio_pcm_substream *vss = snd_pcm_substream_chip(substream);
> +
> +	if (unlikely(pos + count > vss->buffer_sz))
> +		return -EINVAL;
> +
> +	memset(vss->buffer + pos, 0, count);
> +
> +	return virtsnd_pcm_msg_send_locked(vss, true);
> +}
> +
> +/* PCM substream operators map for playback. */
> +const struct snd_pcm_ops virtsnd_pcm_playback_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,
> +	.sync_stop = virtsnd_pcm_sync_stop,
> +	.pointer = virtsnd_pcm_pointer,
> +	.copy = virtsnd_pcm_pb_copy,
> +	.fill_silence = virtsnd_pcm_pb_silence,
> +};
> +
> +/* PCM substream operators map for capturing. */
> +const struct snd_pcm_ops virtsnd_pcm_capture_ops = {
>  	.open = virtsnd_pcm_open,
>  	.close = virtsnd_pcm_close,
>  	.ioctl = snd_pcm_lib_ioctl,
> @@ -461,4 +532,5 @@ const struct snd_pcm_ops virtsnd_pcm_ops = {
>  	.trigger = virtsnd_pcm_trigger,
>  	.sync_stop = virtsnd_pcm_sync_stop,
>  	.pointer = virtsnd_pcm_pointer,
> +	.copy = virtsnd_pcm_cap_copy,
>  };
> 
> base-commit: 8a749fd1a8720d4619c91c8b6e7528c0a355c0aa
> -- 
> 2.41.0
> 

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Re: [RFC PATCH] ALSA: virtio: use copy and fill_silence callbacks

[Takashi Iwai]

On Mon, 16 Oct 2023 17:10:00 +0200,
Stefan Hajnoczi wrote:
> 
> On Thu, Oct 12, 2023 at 05:10:50PM +0200, Matias Ezequiel Vara Larsen wrote:
> > This commit replaces the mmap mechanism with the copy() and
> > fill_silence() callbacks for both capturing and playback for the
> > virtio-sound driver. This change is required to prevent the updating of
> > the content of a buffer that is already in the available ring.
> > 
> > The current mechanism splits a dma buffer into descriptors that are
> > exposed to the device. This dma buffer is shared with the user
> > application. When the device consumes a buffer, the driver moves the
> > request from the used ring to available ring.
> > 
> > The driver exposes the buffer to the device without knowing if the
> > content has been updated from the user. The section 2.8.21.1 of the
> > virtio spec states that: "The device MAY access the descriptor chains
> > the driver created and the memory they refer to immediately". If the
> > device picks up buffers from the available ring just after it is
> > notified, it happens that the content may be old.
> > 
> > By providing the copy() callback, the driver first updates the content
> > of the buffer, and then, exposes the buffer to the device by enqueuing
> > it in the available ring. Thus, device always picks up a buffer that is
> > updated.
> > 
> > For capturing, the driver starts by exposing all the available buffers
> > to device. After device updates the content of a buffer, it enqueues it
> > in the used ring. It is only after the copy() for capturing is issued
> > that the driver re-enqueues the buffer in the available ring.
> > 
> > Note that the copy() function assumes that user is always writing a
> > period. Testing shows that this is true but I may be wrong. This RFC
> > aims at clarifying this.
> 
> This sounds like an ALSA driver API question.
> 
> Jaroslav and Takashi: Any thoughts?

The size of the transfer is determined solely by PCM appl_ptr and
hw_ptr values.  The former is what applications update via the mmap
commit or the normal read/write operations, while the latter is
updated via PCM position() op.  So basically the granularity depends
on the values returned from PCM position op.


Takashi

> 
> Stefan
> 
> > 
> > Signed-off-by: Matias Ezequiel Vara Larsen <mvaralar@redhat.com>
> > ---
> >  sound/virtio/virtio_pcm.c     | 11 ++--
> >  sound/virtio/virtio_pcm.h     |  9 +++-
> >  sound/virtio/virtio_pcm_msg.c | 50 ++++++++++++++++---
> >  sound/virtio/virtio_pcm_ops.c | 94 +++++++++++++++++++++++++++++++----
> >  4 files changed, 137 insertions(+), 27 deletions(-)
> > 
> > diff --git a/sound/virtio/virtio_pcm.c b/sound/virtio/virtio_pcm.c
> > index c10d91fff2fb..bfe982952303 100644
> > --- a/sound/virtio/virtio_pcm.c
> > +++ b/sound/virtio/virtio_pcm.c
> > @@ -104,8 +104,6 @@ static int virtsnd_pcm_build_hw(struct virtio_pcm_substream *vss,
> >  	 * only message-based transport.
> >  	 */
> >  	vss->hw.info =
> > -		SNDRV_PCM_INFO_MMAP |
> > -		SNDRV_PCM_INFO_MMAP_VALID |
> >  		SNDRV_PCM_INFO_BATCH |
> >  		SNDRV_PCM_INFO_BLOCK_TRANSFER |
> >  		SNDRV_PCM_INFO_INTERLEAVED |
> > @@ -471,12 +469,11 @@ int virtsnd_pcm_build_devs(struct virtio_snd *snd)
> >  			for (kss = ks->substream; kss; kss = kss->next)
> >  				vs->substreams[kss->number]->substream = kss;
> >  
> > -			snd_pcm_set_ops(vpcm->pcm, i, &virtsnd_pcm_ops);
> > +			if (i == SNDRV_PCM_STREAM_CAPTURE)
> > +				snd_pcm_set_ops(vpcm->pcm, i, &virtsnd_pcm_capture_ops);
> > +			else
> > +				snd_pcm_set_ops(vpcm->pcm, i, &virtsnd_pcm_playback_ops);
> >  		}
> > -
> > -		snd_pcm_set_managed_buffer_all(vpcm->pcm,
> > -					       SNDRV_DMA_TYPE_VMALLOC, NULL,
> > -					       0, 0);
> >  	}
> >  
> >  	return 0;
> > diff --git a/sound/virtio/virtio_pcm.h b/sound/virtio/virtio_pcm.h
> > index 062eb8e8f2cf..1c1106ec971f 100644
> > --- a/sound/virtio/virtio_pcm.h
> > +++ b/sound/virtio/virtio_pcm.h
> > @@ -50,6 +50,8 @@ struct virtio_pcm_substream {
> >  	struct work_struct elapsed_period;
> >  	spinlock_t lock;
> >  	size_t buffer_bytes;
> > +	u8 *buffer;
> > +	size_t buffer_sz;
> >  	size_t hw_ptr;
> >  	bool xfer_enabled;
> >  	bool xfer_xrun;
> > @@ -90,7 +92,8 @@ struct virtio_pcm {
> >  	struct virtio_pcm_stream streams[SNDRV_PCM_STREAM_LAST + 1];
> >  };
> >  
> > -extern const struct snd_pcm_ops virtsnd_pcm_ops;
> > +extern const struct snd_pcm_ops virtsnd_pcm_playback_ops;
> > +extern const struct snd_pcm_ops virtsnd_pcm_capture_ops;
> >  
> >  int virtsnd_pcm_validate(struct virtio_device *vdev);
> >  
> > @@ -117,7 +120,9 @@ int virtsnd_pcm_msg_alloc(struct virtio_pcm_substream *vss,
> >  
> >  void virtsnd_pcm_msg_free(struct virtio_pcm_substream *vss);
> >  
> > -int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss);
> > +int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss, bool single);
> > +
> > +int virtsnd_pcm_msg_send_locked(struct virtio_pcm_substream *vss, bool single);
> >  
> >  unsigned int virtsnd_pcm_msg_pending_num(struct virtio_pcm_substream *vss);
> >  
> > diff --git a/sound/virtio/virtio_pcm_msg.c b/sound/virtio/virtio_pcm_msg.c
> > index aca2dc1989ba..9a5f9814cb62 100644
> > --- a/sound/virtio/virtio_pcm_msg.c
> > +++ b/sound/virtio/virtio_pcm_msg.c
> > @@ -132,7 +132,6 @@ static void virtsnd_pcm_sg_from(struct scatterlist *sgs, int nsgs, u8 *data,
> >  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;
> >  
> >  	vss->msgs = kcalloc(periods, sizeof(*vss->msgs), GFP_KERNEL);
> > @@ -142,7 +141,7 @@ int virtsnd_pcm_msg_alloc(struct virtio_pcm_substream *vss,
> >  	vss->nmsgs = periods;
> >  
> >  	for (i = 0; i < periods; ++i) {
> > -		u8 *data = runtime->dma_area + period_bytes * i;
> > +		u8 *data = vss->buffer + period_bytes * i;
> >  		int sg_num = virtsnd_pcm_sg_num(data, period_bytes);
> >  		struct virtio_pcm_msg *msg;
> >  
> > @@ -186,10 +185,12 @@ void virtsnd_pcm_msg_free(struct virtio_pcm_substream *vss)
> >  /**
> >   * virtsnd_pcm_msg_send() - Send asynchronous I/O messages.
> >   * @vss: VirtIO PCM substream.
> > + * @single: true to enqueue a single message, false to enqueue all of them.
> >   *
> >   * 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:
> > + * function is called, first non-enqueued message is added to the virtqueue.
> > + * When single is True, only the first message is enqueued. When False, all the
> > + * available messages are enqueued.  The function keeps track of two values:
> >   *
> >   *   msg_last_enqueued = index of the last enqueued message,
> >   *   msg_count = # of pending messages in the virtqueue.
> > @@ -198,7 +199,7 @@ void virtsnd_pcm_msg_free(struct virtio_pcm_substream *vss)
> >   *          spinlocks to be held by caller.
> >   * Return: 0 on success, -errno on failure.
> >   */
> > -int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss)
> > +int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss, bool single)
> >  {
> >  	struct snd_pcm_runtime *runtime = vss->substream->runtime;
> >  	struct virtio_snd *snd = vss->snd;
> > @@ -211,6 +212,13 @@ int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss)
> >  	i = (vss->msg_last_enqueued + 1) % runtime->periods;
> >  	n = runtime->periods - vss->msg_count;
> >  
> > +	if (single) {
> > +		if (n < 1)
> > +			return -EFAULT;
> > +
> > +		n = 1;
> > +	}
> > +
> >  	for (; n; --n, i = (i + 1) % runtime->periods) {
> >  		struct virtio_pcm_msg *msg = vss->msgs[i];
> >  		struct scatterlist *psgs[] = {
> > @@ -250,6 +258,36 @@ int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss)
> >  	return 0;
> >  }
> >  
> > +/**
> > + * virtsnd_pcm_msg_send_locked() - Send asynchronous I/O messages.
> > + * @vss: VirtIO PCM substream.
> > + * @single: true to enqueue a single message, false to enqueue all of them.
> > + *
> > + * This function holds the tx/rx queue and the VirtIO substream spinlocks
> > + * before calling virtsnd_pcm_msg_send(). This is a wrapper function to ease
> > + * the invocation of virtsnd_pcm_msg_send().
> > + *
> > + * Context: Any context.
> > + * Return: 0 on success, -errno on failure.
> > + */
> > +
> > +int virtsnd_pcm_msg_send_locked(struct virtio_pcm_substream *vss, bool single)
> > +{
> > +	struct virtio_snd_queue *queue;
> > +	int rc;
> > +	unsigned long flags;
> > +
> > +	queue = virtsnd_pcm_queue(vss);
> > +
> > +	spin_lock_irqsave(&queue->lock, flags);
> > +	spin_lock(&vss->lock);
> > +	rc = virtsnd_pcm_msg_send(vss, single);
> > +	spin_unlock(&vss->lock);
> > +	spin_unlock_irqrestore(&queue->lock, flags);
> > +
> > +	return rc;
> > +}
> > +
> >  /**
> >   * virtsnd_pcm_msg_pending_num() - Returns the number of pending I/O messages.
> >   * @vss: VirtIO substream.
> > @@ -320,8 +358,6 @@ static void virtsnd_pcm_msg_complete(struct virtio_pcm_msg *msg,
> >  					le32_to_cpu(msg->status.latency_bytes));
> >  
> >  		schedule_work(&vss->elapsed_period);
> > -
> > -		virtsnd_pcm_msg_send(vss);
> >  	} else if (!vss->msg_count) {
> >  		wake_up_all(&vss->msg_empty);
> >  	}
> > diff --git a/sound/virtio/virtio_pcm_ops.c b/sound/virtio/virtio_pcm_ops.c
> > index f8bfb87624be..a208439dbff8 100644
> > --- a/sound/virtio/virtio_pcm_ops.c
> > +++ b/sound/virtio/virtio_pcm_ops.c
> > @@ -238,6 +238,11 @@ static int virtsnd_pcm_hw_params(struct snd_pcm_substream *substream,
> >  	 */
> >  	virtsnd_pcm_msg_free(vss);
> >  
> > +	vss->buffer_sz = params_buffer_bytes(hw_params);
> > +	vss->buffer = alloc_pages_exact(vss->buffer_sz, GFP_KERNEL);
> > +	if (!vss->buffer)
> > +		return -ENOMEM;
> > +
> >  	return virtsnd_pcm_msg_alloc(vss, params_periods(hw_params),
> >  				     params_period_bytes(hw_params));
> >  }
> > @@ -257,6 +262,11 @@ static int virtsnd_pcm_hw_free(struct snd_pcm_substream *substream)
> >  	if (!virtsnd_pcm_msg_pending_num(vss))
> >  		virtsnd_pcm_msg_free(vss);
> >  
> > +	if (vss->buffer) {
> > +		free_pages_exact(vss->buffer, vss->buffer_sz);
> > +		vss->buffer = NULL;
> > +	}
> > +
> >  	return 0;
> >  }
> >  
> > @@ -331,15 +341,18 @@ static int virtsnd_pcm_trigger(struct snd_pcm_substream *substream, int command)
> >  	case SNDRV_PCM_TRIGGER_PAUSE_RELEASE:
> >  		queue = virtsnd_pcm_queue(vss);
> >  
> > -		spin_lock_irqsave(&queue->lock, flags);
> > -		spin_lock(&vss->lock);
> > -		rc = virtsnd_pcm_msg_send(vss);
> > -		if (!rc)
> > -			vss->xfer_enabled = true;
> > -		spin_unlock(&vss->lock);
> > -		spin_unlock_irqrestore(&queue->lock, flags);
> > -		if (rc)
> > -			return rc;
> > +		// The buffers should be exposed first during capturing so that
> > +		// the device can consume them. Capturing cannot begin
> > +		// otherwise.
> > +		if (vss->direction == SNDRV_PCM_STREAM_CAPTURE) {
> > +			rc = virtsnd_pcm_msg_send_locked(vss, false);
> > +			if (rc)
> > +				return rc;
> > +		}
> > +
> > +		spin_lock_irqsave(&vss->lock, flags);
> > +		vss->xfer_enabled = true;
> > +		spin_unlock_irqrestore(&vss->lock, flags);
> >  
> >  		msg = virtsnd_pcm_ctl_msg_alloc(vss, VIRTIO_SND_R_PCM_START,
> >  						GFP_KERNEL);
> > @@ -450,8 +463,66 @@ virtsnd_pcm_pointer(struct snd_pcm_substream *substream)
> >  	return hw_ptr;
> >  }
> >  
> > -/* PCM substream operators map. */
> > -const struct snd_pcm_ops virtsnd_pcm_ops = {
> > +static int virtsnd_pcm_pb_copy(struct snd_pcm_substream *substream,
> > +			       int channel, unsigned long pos, struct iov_iter
> > +			       *src, unsigned long count)
> > +{
> > +	struct virtio_pcm_substream *vss = snd_pcm_substream_chip(substream);
> > +
> > +	if (unlikely(pos + count > vss->buffer_sz))
> > +		return -EINVAL;
> > +
> > +	if (copy_from_iter(vss->buffer + pos, count, src) != count)
> > +		return -EFAULT;
> > +
> > +	return virtsnd_pcm_msg_send_locked(vss, true);
> > +}
> > +
> > +static int virtsnd_pcm_cap_copy(struct snd_pcm_substream *substream,
> > +				int channel, unsigned long pos, struct iov_iter
> > +				*dst, unsigned long count)
> > +{
> > +	struct virtio_pcm_substream *vss = snd_pcm_substream_chip(substream);
> > +
> > +	if (unlikely(pos + count > vss->buffer_sz))
> > +		return -EINVAL;
> > +
> > +	if (copy_to_iter(vss->buffer + pos, count, dst) != count)
> > +		return -EFAULT;
> > +
> > +	return virtsnd_pcm_msg_send_locked(vss, true);
> > +}
> > +
> > +static int virtsnd_pcm_pb_silence(struct snd_pcm_substream *substream, int channel,
> > +				  unsigned long pos, unsigned long count)
> > +{
> > +	struct virtio_pcm_substream *vss = snd_pcm_substream_chip(substream);
> > +
> > +	if (unlikely(pos + count > vss->buffer_sz))
> > +		return -EINVAL;
> > +
> > +	memset(vss->buffer + pos, 0, count);
> > +
> > +	return virtsnd_pcm_msg_send_locked(vss, true);
> > +}
> > +
> > +/* PCM substream operators map for playback. */
> > +const struct snd_pcm_ops virtsnd_pcm_playback_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,
> > +	.sync_stop = virtsnd_pcm_sync_stop,
> > +	.pointer = virtsnd_pcm_pointer,
> > +	.copy = virtsnd_pcm_pb_copy,
> > +	.fill_silence = virtsnd_pcm_pb_silence,
> > +};
> > +
> > +/* PCM substream operators map for capturing. */
> > +const struct snd_pcm_ops virtsnd_pcm_capture_ops = {
> >  	.open = virtsnd_pcm_open,
> >  	.close = virtsnd_pcm_close,
> >  	.ioctl = snd_pcm_lib_ioctl,
> > @@ -461,4 +532,5 @@ const struct snd_pcm_ops virtsnd_pcm_ops = {
> >  	.trigger = virtsnd_pcm_trigger,
> >  	.sync_stop = virtsnd_pcm_sync_stop,
> >  	.pointer = virtsnd_pcm_pointer,
> > +	.copy = virtsnd_pcm_cap_copy,
> >  };
> > 
> > base-commit: 8a749fd1a8720d4619c91c8b6e7528c0a355c0aa
> > -- 
> > 2.41.0
> > 
> Verifying...

Re: [RFC PATCH] ALSA: virtio: use copy and fill_silence callbacks

[Matias Ezequiel Vara Larsen]

On Tue, Oct 17, 2023 at 09:44:04AM +0200, Takashi Iwai wrote:
> On Mon, 16 Oct 2023 17:10:00 +0200,
> Stefan Hajnoczi wrote:
> > 
> > On Thu, Oct 12, 2023 at 05:10:50PM +0200, Matias Ezequiel Vara Larsen wrote:
> > > This commit replaces the mmap mechanism with the copy() and
> > > fill_silence() callbacks for both capturing and playback for the
> > > virtio-sound driver. This change is required to prevent the updating of
> > > the content of a buffer that is already in the available ring.
> > > 
> > > The current mechanism splits a dma buffer into descriptors that are
> > > exposed to the device. This dma buffer is shared with the user
> > > application. When the device consumes a buffer, the driver moves the
> > > request from the used ring to available ring.
> > > 
> > > The driver exposes the buffer to the device without knowing if the
> > > content has been updated from the user. The section 2.8.21.1 of the
> > > virtio spec states that: "The device MAY access the descriptor chains
> > > the driver created and the memory they refer to immediately". If the
> > > device picks up buffers from the available ring just after it is
> > > notified, it happens that the content may be old.
> > > 
> > > By providing the copy() callback, the driver first updates the content
> > > of the buffer, and then, exposes the buffer to the device by enqueuing
> > > it in the available ring. Thus, device always picks up a buffer that is
> > > updated.
> > > 
> > > For capturing, the driver starts by exposing all the available buffers
> > > to device. After device updates the content of a buffer, it enqueues it
> > > in the used ring. It is only after the copy() for capturing is issued
> > > that the driver re-enqueues the buffer in the available ring.
> > > 
> > > Note that the copy() function assumes that user is always writing a
> > > period. Testing shows that this is true but I may be wrong. This RFC
> > > aims at clarifying this.
> > 
> > This sounds like an ALSA driver API question.
> > 
> > Jaroslav and Takashi: Any thoughts?
> 
> The size of the transfer is determined solely by PCM appl_ptr and
> hw_ptr values.  The former is what applications update via the mmap
> commit or the normal read/write operations, while the latter is
> updated via PCM position() op.  So basically the granularity depends
> on the values returned from PCM position op.
> 
> 

Thanks for your comment, I'll send a second version without the
assumption that applications always update a single period.

Matias

> Takashi
> 
> > 
> > Stefan
> > 
> > > 
> > > Signed-off-by: Matias Ezequiel Vara Larsen <mvaralar@redhat.com>
> > > ---
> > >  sound/virtio/virtio_pcm.c     | 11 ++--
> > >  sound/virtio/virtio_pcm.h     |  9 +++-
> > >  sound/virtio/virtio_pcm_msg.c | 50 ++++++++++++++++---
> > >  sound/virtio/virtio_pcm_ops.c | 94 +++++++++++++++++++++++++++++++----
> > >  4 files changed, 137 insertions(+), 27 deletions(-)
> > > 
> > > diff --git a/sound/virtio/virtio_pcm.c b/sound/virtio/virtio_pcm.c
> > > index c10d91fff2fb..bfe982952303 100644
> > > --- a/sound/virtio/virtio_pcm.c
> > > +++ b/sound/virtio/virtio_pcm.c
> > > @@ -104,8 +104,6 @@ static int virtsnd_pcm_build_hw(struct virtio_pcm_substream *vss,
> > >  	 * only message-based transport.
> > >  	 */
> > >  	vss->hw.info =
> > > -		SNDRV_PCM_INFO_MMAP |
> > > -		SNDRV_PCM_INFO_MMAP_VALID |
> > >  		SNDRV_PCM_INFO_BATCH |
> > >  		SNDRV_PCM_INFO_BLOCK_TRANSFER |
> > >  		SNDRV_PCM_INFO_INTERLEAVED |
> > > @@ -471,12 +469,11 @@ int virtsnd_pcm_build_devs(struct virtio_snd *snd)
> > >  			for (kss = ks->substream; kss; kss = kss->next)
> > >  				vs->substreams[kss->number]->substream = kss;
> > >  
> > > -			snd_pcm_set_ops(vpcm->pcm, i, &virtsnd_pcm_ops);
> > > +			if (i == SNDRV_PCM_STREAM_CAPTURE)
> > > +				snd_pcm_set_ops(vpcm->pcm, i, &virtsnd_pcm_capture_ops);
> > > +			else
> > > +				snd_pcm_set_ops(vpcm->pcm, i, &virtsnd_pcm_playback_ops);
> > >  		}
> > > -
> > > -		snd_pcm_set_managed_buffer_all(vpcm->pcm,
> > > -					       SNDRV_DMA_TYPE_VMALLOC, NULL,
> > > -					       0, 0);
> > >  	}
> > >  
> > >  	return 0;
> > > diff --git a/sound/virtio/virtio_pcm.h b/sound/virtio/virtio_pcm.h
> > > index 062eb8e8f2cf..1c1106ec971f 100644
> > > --- a/sound/virtio/virtio_pcm.h
> > > +++ b/sound/virtio/virtio_pcm.h
> > > @@ -50,6 +50,8 @@ struct virtio_pcm_substream {
> > >  	struct work_struct elapsed_period;
> > >  	spinlock_t lock;
> > >  	size_t buffer_bytes;
> > > +	u8 *buffer;
> > > +	size_t buffer_sz;
> > >  	size_t hw_ptr;
> > >  	bool xfer_enabled;
> > >  	bool xfer_xrun;
> > > @@ -90,7 +92,8 @@ struct virtio_pcm {
> > >  	struct virtio_pcm_stream streams[SNDRV_PCM_STREAM_LAST + 1];
> > >  };
> > >  
> > > -extern const struct snd_pcm_ops virtsnd_pcm_ops;
> > > +extern const struct snd_pcm_ops virtsnd_pcm_playback_ops;
> > > +extern const struct snd_pcm_ops virtsnd_pcm_capture_ops;
> > >  
> > >  int virtsnd_pcm_validate(struct virtio_device *vdev);
> > >  
> > > @@ -117,7 +120,9 @@ int virtsnd_pcm_msg_alloc(struct virtio_pcm_substream *vss,
> > >  
> > >  void virtsnd_pcm_msg_free(struct virtio_pcm_substream *vss);
> > >  
> > > -int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss);
> > > +int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss, bool single);
> > > +
> > > +int virtsnd_pcm_msg_send_locked(struct virtio_pcm_substream *vss, bool single);
> > >  
> > >  unsigned int virtsnd_pcm_msg_pending_num(struct virtio_pcm_substream *vss);
> > >  
> > > diff --git a/sound/virtio/virtio_pcm_msg.c b/sound/virtio/virtio_pcm_msg.c
> > > index aca2dc1989ba..9a5f9814cb62 100644
> > > --- a/sound/virtio/virtio_pcm_msg.c
> > > +++ b/sound/virtio/virtio_pcm_msg.c
> > > @@ -132,7 +132,6 @@ static void virtsnd_pcm_sg_from(struct scatterlist *sgs, int nsgs, u8 *data,
> > >  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;
> > >  
> > >  	vss->msgs = kcalloc(periods, sizeof(*vss->msgs), GFP_KERNEL);
> > > @@ -142,7 +141,7 @@ int virtsnd_pcm_msg_alloc(struct virtio_pcm_substream *vss,
> > >  	vss->nmsgs = periods;
> > >  
> > >  	for (i = 0; i < periods; ++i) {
> > > -		u8 *data = runtime->dma_area + period_bytes * i;
> > > +		u8 *data = vss->buffer + period_bytes * i;
> > >  		int sg_num = virtsnd_pcm_sg_num(data, period_bytes);
> > >  		struct virtio_pcm_msg *msg;
> > >  
> > > @@ -186,10 +185,12 @@ void virtsnd_pcm_msg_free(struct virtio_pcm_substream *vss)
> > >  /**
> > >   * virtsnd_pcm_msg_send() - Send asynchronous I/O messages.
> > >   * @vss: VirtIO PCM substream.
> > > + * @single: true to enqueue a single message, false to enqueue all of them.
> > >   *
> > >   * 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:
> > > + * function is called, first non-enqueued message is added to the virtqueue.
> > > + * When single is True, only the first message is enqueued. When False, all the
> > > + * available messages are enqueued.  The function keeps track of two values:
> > >   *
> > >   *   msg_last_enqueued = index of the last enqueued message,
> > >   *   msg_count = # of pending messages in the virtqueue.
> > > @@ -198,7 +199,7 @@ void virtsnd_pcm_msg_free(struct virtio_pcm_substream *vss)
> > >   *          spinlocks to be held by caller.
> > >   * Return: 0 on success, -errno on failure.
> > >   */
> > > -int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss)
> > > +int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss, bool single)
> > >  {
> > >  	struct snd_pcm_runtime *runtime = vss->substream->runtime;
> > >  	struct virtio_snd *snd = vss->snd;
> > > @@ -211,6 +212,13 @@ int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss)
> > >  	i = (vss->msg_last_enqueued + 1) % runtime->periods;
> > >  	n = runtime->periods - vss->msg_count;
> > >  
> > > +	if (single) {
> > > +		if (n < 1)
> > > +			return -EFAULT;
> > > +
> > > +		n = 1;
> > > +	}
> > > +
> > >  	for (; n; --n, i = (i + 1) % runtime->periods) {
> > >  		struct virtio_pcm_msg *msg = vss->msgs[i];
> > >  		struct scatterlist *psgs[] = {
> > > @@ -250,6 +258,36 @@ int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss)
> > >  	return 0;
> > >  }
> > >  
> > > +/**
> > > + * virtsnd_pcm_msg_send_locked() - Send asynchronous I/O messages.
> > > + * @vss: VirtIO PCM substream.
> > > + * @single: true to enqueue a single message, false to enqueue all of them.
> > > + *
> > > + * This function holds the tx/rx queue and the VirtIO substream spinlocks
> > > + * before calling virtsnd_pcm_msg_send(). This is a wrapper function to ease
> > > + * the invocation of virtsnd_pcm_msg_send().
> > > + *
> > > + * Context: Any context.
> > > + * Return: 0 on success, -errno on failure.
> > > + */
> > > +
> > > +int virtsnd_pcm_msg_send_locked(struct virtio_pcm_substream *vss, bool single)
> > > +{
> > > +	struct virtio_snd_queue *queue;
> > > +	int rc;
> > > +	unsigned long flags;
> > > +
> > > +	queue = virtsnd_pcm_queue(vss);
> > > +
> > > +	spin_lock_irqsave(&queue->lock, flags);
> > > +	spin_lock(&vss->lock);
> > > +	rc = virtsnd_pcm_msg_send(vss, single);
> > > +	spin_unlock(&vss->lock);
> > > +	spin_unlock_irqrestore(&queue->lock, flags);
> > > +
> > > +	return rc;
> > > +}
> > > +
> > >  /**
> > >   * virtsnd_pcm_msg_pending_num() - Returns the number of pending I/O messages.
> > >   * @vss: VirtIO substream.
> > > @@ -320,8 +358,6 @@ static void virtsnd_pcm_msg_complete(struct virtio_pcm_msg *msg,
> > >  					le32_to_cpu(msg->status.latency_bytes));
> > >  
> > >  		schedule_work(&vss->elapsed_period);
> > > -
> > > -		virtsnd_pcm_msg_send(vss);
> > >  	} else if (!vss->msg_count) {
> > >  		wake_up_all(&vss->msg_empty);
> > >  	}
> > > diff --git a/sound/virtio/virtio_pcm_ops.c b/sound/virtio/virtio_pcm_ops.c
> > > index f8bfb87624be..a208439dbff8 100644
> > > --- a/sound/virtio/virtio_pcm_ops.c
> > > +++ b/sound/virtio/virtio_pcm_ops.c
> > > @@ -238,6 +238,11 @@ static int virtsnd_pcm_hw_params(struct snd_pcm_substream *substream,
> > >  	 */
> > >  	virtsnd_pcm_msg_free(vss);
> > >  
> > > +	vss->buffer_sz = params_buffer_bytes(hw_params);
> > > +	vss->buffer = alloc_pages_exact(vss->buffer_sz, GFP_KERNEL);
> > > +	if (!vss->buffer)
> > > +		return -ENOMEM;
> > > +
> > >  	return virtsnd_pcm_msg_alloc(vss, params_periods(hw_params),
> > >  				     params_period_bytes(hw_params));
> > >  }
> > > @@ -257,6 +262,11 @@ static int virtsnd_pcm_hw_free(struct snd_pcm_substream *substream)
> > >  	if (!virtsnd_pcm_msg_pending_num(vss))
> > >  		virtsnd_pcm_msg_free(vss);
> > >  
> > > +	if (vss->buffer) {
> > > +		free_pages_exact(vss->buffer, vss->buffer_sz);
> > > +		vss->buffer = NULL;
> > > +	}
> > > +
> > >  	return 0;
> > >  }
> > >  
> > > @@ -331,15 +341,18 @@ static int virtsnd_pcm_trigger(struct snd_pcm_substream *substream, int command)
> > >  	case SNDRV_PCM_TRIGGER_PAUSE_RELEASE:
> > >  		queue = virtsnd_pcm_queue(vss);
> > >  
> > > -		spin_lock_irqsave(&queue->lock, flags);
> > > -		spin_lock(&vss->lock);
> > > -		rc = virtsnd_pcm_msg_send(vss);
> > > -		if (!rc)
> > > -			vss->xfer_enabled = true;
> > > -		spin_unlock(&vss->lock);
> > > -		spin_unlock_irqrestore(&queue->lock, flags);
> > > -		if (rc)
> > > -			return rc;
> > > +		// The buffers should be exposed first during capturing so that
> > > +		// the device can consume them. Capturing cannot begin
> > > +		// otherwise.
> > > +		if (vss->direction == SNDRV_PCM_STREAM_CAPTURE) {
> > > +			rc = virtsnd_pcm_msg_send_locked(vss, false);
> > > +			if (rc)
> > > +				return rc;
> > > +		}
> > > +
> > > +		spin_lock_irqsave(&vss->lock, flags);
> > > +		vss->xfer_enabled = true;
> > > +		spin_unlock_irqrestore(&vss->lock, flags);
> > >  
> > >  		msg = virtsnd_pcm_ctl_msg_alloc(vss, VIRTIO_SND_R_PCM_START,
> > >  						GFP_KERNEL);
> > > @@ -450,8 +463,66 @@ virtsnd_pcm_pointer(struct snd_pcm_substream *substream)
> > >  	return hw_ptr;
> > >  }
> > >  
> > > -/* PCM substream operators map. */
> > > -const struct snd_pcm_ops virtsnd_pcm_ops = {
> > > +static int virtsnd_pcm_pb_copy(struct snd_pcm_substream *substream,
> > > +			       int channel, unsigned long pos, struct iov_iter
> > > +			       *src, unsigned long count)
> > > +{
> > > +	struct virtio_pcm_substream *vss = snd_pcm_substream_chip(substream);
> > > +
> > > +	if (unlikely(pos + count > vss->buffer_sz))
> > > +		return -EINVAL;
> > > +
> > > +	if (copy_from_iter(vss->buffer + pos, count, src) != count)
> > > +		return -EFAULT;
> > > +
> > > +	return virtsnd_pcm_msg_send_locked(vss, true);
> > > +}
> > > +
> > > +static int virtsnd_pcm_cap_copy(struct snd_pcm_substream *substream,
> > > +				int channel, unsigned long pos, struct iov_iter
> > > +				*dst, unsigned long count)
> > > +{
> > > +	struct virtio_pcm_substream *vss = snd_pcm_substream_chip(substream);
> > > +
> > > +	if (unlikely(pos + count > vss->buffer_sz))
> > > +		return -EINVAL;
> > > +
> > > +	if (copy_to_iter(vss->buffer + pos, count, dst) != count)
> > > +		return -EFAULT;
> > > +
> > > +	return virtsnd_pcm_msg_send_locked(vss, true);
> > > +}
> > > +
> > > +static int virtsnd_pcm_pb_silence(struct snd_pcm_substream *substream, int channel,
> > > +				  unsigned long pos, unsigned long count)
> > > +{
> > > +	struct virtio_pcm_substream *vss = snd_pcm_substream_chip(substream);
> > > +
> > > +	if (unlikely(pos + count > vss->buffer_sz))
> > > +		return -EINVAL;
> > > +
> > > +	memset(vss->buffer + pos, 0, count);
> > > +
> > > +	return virtsnd_pcm_msg_send_locked(vss, true);
> > > +}
> > > +
> > > +/* PCM substream operators map for playback. */
> > > +const struct snd_pcm_ops virtsnd_pcm_playback_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,
> > > +	.sync_stop = virtsnd_pcm_sync_stop,
> > > +	.pointer = virtsnd_pcm_pointer,
> > > +	.copy = virtsnd_pcm_pb_copy,
> > > +	.fill_silence = virtsnd_pcm_pb_silence,
> > > +};
> > > +
> > > +/* PCM substream operators map for capturing. */
> > > +const struct snd_pcm_ops virtsnd_pcm_capture_ops = {
> > >  	.open = virtsnd_pcm_open,
> > >  	.close = virtsnd_pcm_close,
> > >  	.ioctl = snd_pcm_lib_ioctl,
> > > @@ -461,4 +532,5 @@ const struct snd_pcm_ops virtsnd_pcm_ops = {
> > >  	.trigger = virtsnd_pcm_trigger,
> > >  	.sync_stop = virtsnd_pcm_sync_stop,
> > >  	.pointer = virtsnd_pcm_pointer,
> > > +	.copy = virtsnd_pcm_cap_copy,
> > >  };
> > > 
> > > base-commit: 8a749fd1a8720d4619c91c8b6e7528c0a355c0aa
> > > -- 
> > > 2.41.0
> > > 
> > Verifying...
> 

Re: [RFC PATCH] ALSA: virtio: use copy and fill_silence callbacks

[Anton Yakovlev]

[-- Attachment #1: Type: text/plain, Size: 13668 bytes --]

Hi Matias,

Thanks for your help! I updated and corrected your patch a little bit (see
attachment). All changes were tested, there were no problems on my side.

See also a few inline comments.



On 13.10.2023 00:10, Matias Ezequiel Vara Larsen wrote:
> This commit replaces the mmap mechanism with the copy() and
> fill_silence() callbacks for both capturing and playback for the
> virtio-sound driver. This change is required to prevent the updating of
> the content of a buffer that is already in the available ring.
> 
> The current mechanism splits a dma buffer into descriptors that are
> exposed to the device. This dma buffer is shared with the user
> application. When the device consumes a buffer, the driver moves the
> request from the used ring to available ring.
> 
> The driver exposes the buffer to the device without knowing if the
> content has been updated from the user. The section 2.8.21.1 of the
> virtio spec states that: "The device MAY access the descriptor chains
> the driver created and the memory they refer to immediately". If the
> device picks up buffers from the available ring just after it is
> notified, it happens that the content may be old.
> 
> By providing the copy() callback, the driver first updates the content
> of the buffer, and then, exposes the buffer to the device by enqueuing
> it in the available ring. Thus, device always picks up a buffer that is
> updated.
> 
> For capturing, the driver starts by exposing all the available buffers
> to device. After device updates the content of a buffer, it enqueues it
> in the used ring. It is only after the copy() for capturing is issued
> that the driver re-enqueues the buffer in the available ring.
> 
> Note that the copy() function assumes that user is always writing a
> period. Testing shows that this is true but I may be wrong. This RFC
> aims at clarifying this.
> 
> Signed-off-by: Matias Ezequiel Vara Larsen <mvaralar@redhat.com>
> ---
>   sound/virtio/virtio_pcm.c     | 11 ++--
>   sound/virtio/virtio_pcm.h     |  9 +++-
>   sound/virtio/virtio_pcm_msg.c | 50 ++++++++++++++++---
>   sound/virtio/virtio_pcm_ops.c | 94 +++++++++++++++++++++++++++++++----
>   4 files changed, 137 insertions(+), 27 deletions(-)
> 
> diff --git a/sound/virtio/virtio_pcm.c b/sound/virtio/virtio_pcm.c
> index c10d91fff2fb..bfe982952303 100644
> --- a/sound/virtio/virtio_pcm.c
> +++ b/sound/virtio/virtio_pcm.c
> @@ -104,8 +104,6 @@ static int virtsnd_pcm_build_hw(struct virtio_pcm_substream *vss,
>   	 * only message-based transport.
>   	 */
>   	vss->hw.info =
> -		SNDRV_PCM_INFO_MMAP |
> -		SNDRV_PCM_INFO_MMAP_VALID |
>   		SNDRV_PCM_INFO_BATCH |
>   		SNDRV_PCM_INFO_BLOCK_TRANSFER |
>   		SNDRV_PCM_INFO_INTERLEAVED |

We need also necessary to disable rewinds, since now only sequential
reading/writing of frames is supported.


> @@ -471,12 +469,11 @@ int virtsnd_pcm_build_devs(struct virtio_snd *snd)
>   			for (kss = ks->substream; kss; kss = kss->next)
>   				vs->substreams[kss->number]->substream = kss;
>   
> -			snd_pcm_set_ops(vpcm->pcm, i, &virtsnd_pcm_ops);
> +			if (i == SNDRV_PCM_STREAM_CAPTURE)
> +				snd_pcm_set_ops(vpcm->pcm, i, &virtsnd_pcm_capture_ops);
> +			else
> +				snd_pcm_set_ops(vpcm->pcm, i, &virtsnd_pcm_playback_ops);
>   		}
> -
> -		snd_pcm_set_managed_buffer_all(vpcm->pcm,
> -					       SNDRV_DMA_TYPE_VMALLOC, NULL,
> -					       0, 0);

It is not right. Buffer allocation/freeing is controlled by the kernel
subsystem, so the driver doesn't have to worry about it.


>   	}
>   
>   	return 0;
> diff --git a/sound/virtio/virtio_pcm.h b/sound/virtio/virtio_pcm.h
> index 062eb8e8f2cf..1c1106ec971f 100644
> --- a/sound/virtio/virtio_pcm.h
> +++ b/sound/virtio/virtio_pcm.h
> @@ -50,6 +50,8 @@ struct virtio_pcm_substream {
>   	struct work_struct elapsed_period;
>   	spinlock_t lock;
>   	size_t buffer_bytes;
> +	u8 *buffer;
> +	size_t buffer_sz;
>   	size_t hw_ptr;
>   	bool xfer_enabled;
>   	bool xfer_xrun;
> @@ -90,7 +92,8 @@ struct virtio_pcm {
>   	struct virtio_pcm_stream streams[SNDRV_PCM_STREAM_LAST + 1];
>   };
>   
> -extern const struct snd_pcm_ops virtsnd_pcm_ops;
> +extern const struct snd_pcm_ops virtsnd_pcm_playback_ops;
> +extern const struct snd_pcm_ops virtsnd_pcm_capture_ops;
>   
>   int virtsnd_pcm_validate(struct virtio_device *vdev);
>   
> @@ -117,7 +120,9 @@ int virtsnd_pcm_msg_alloc(struct virtio_pcm_substream *vss,
>   
>   void virtsnd_pcm_msg_free(struct virtio_pcm_substream *vss);
>   
> -int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss);
> +int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss, bool single);
> +
> +int virtsnd_pcm_msg_send_locked(struct virtio_pcm_substream *vss, bool single);
>   
>   unsigned int virtsnd_pcm_msg_pending_num(struct virtio_pcm_substream *vss);
>   
> diff --git a/sound/virtio/virtio_pcm_msg.c b/sound/virtio/virtio_pcm_msg.c
> index aca2dc1989ba..9a5f9814cb62 100644
> --- a/sound/virtio/virtio_pcm_msg.c
> +++ b/sound/virtio/virtio_pcm_msg.c
> @@ -132,7 +132,6 @@ static void virtsnd_pcm_sg_from(struct scatterlist *sgs, int nsgs, u8 *data,
>   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;
>   
>   	vss->msgs = kcalloc(periods, sizeof(*vss->msgs), GFP_KERNEL);
> @@ -142,7 +141,7 @@ int virtsnd_pcm_msg_alloc(struct virtio_pcm_substream *vss,
>   	vss->nmsgs = periods;
>   
>   	for (i = 0; i < periods; ++i) {
> -		u8 *data = runtime->dma_area + period_bytes * i;
> +		u8 *data = vss->buffer + period_bytes * i;
>   		int sg_num = virtsnd_pcm_sg_num(data, period_bytes);
>   		struct virtio_pcm_msg *msg;
>   
> @@ -186,10 +185,12 @@ void virtsnd_pcm_msg_free(struct virtio_pcm_substream *vss)
>   /**
>    * virtsnd_pcm_msg_send() - Send asynchronous I/O messages.
>    * @vss: VirtIO PCM substream.
> + * @single: true to enqueue a single message, false to enqueue all of them.
>    *
>    * 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:
> + * function is called, first non-enqueued message is added to the virtqueue.
> + * When single is True, only the first message is enqueued. When False, all the
> + * available messages are enqueued.  The function keeps track of two values:
>    *
>    *   msg_last_enqueued = index of the last enqueued message,
>    *   msg_count = # of pending messages in the virtqueue.
> @@ -198,7 +199,7 @@ void virtsnd_pcm_msg_free(struct virtio_pcm_substream *vss)
>    *          spinlocks to be held by caller.
>    * Return: 0 on success, -errno on failure.
>    */
> -int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss)
> +int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss, bool single)

I would propose to make this function more generic, specifing the offset and
size for the modified part of the buffer. This way no assumptions need to be
made. We can also guarantee that we only put fully written/read messages into
the virtqueue.



>   {
>   	struct snd_pcm_runtime *runtime = vss->substream->runtime;
>   	struct virtio_snd *snd = vss->snd;
> @@ -211,6 +212,13 @@ int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss)
>   	i = (vss->msg_last_enqueued + 1) % runtime->periods;
>   	n = runtime->periods - vss->msg_count;
>   
> +	if (single) {
> +		if (n < 1)
> +			return -EFAULT;
> +
> +		n = 1;
> +	}
> +
>   	for (; n; --n, i = (i + 1) % runtime->periods) {
>   		struct virtio_pcm_msg *msg = vss->msgs[i];
>   		struct scatterlist *psgs[] = {
> @@ -250,6 +258,36 @@ int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss)
>   	return 0;
>   }
>   
> +/**
> + * virtsnd_pcm_msg_send_locked() - Send asynchronous I/O messages.
> + * @vss: VirtIO PCM substream.
> + * @single: true to enqueue a single message, false to enqueue all of them.
> + *
> + * This function holds the tx/rx queue and the VirtIO substream spinlocks
> + * before calling virtsnd_pcm_msg_send(). This is a wrapper function to ease
> + * the invocation of virtsnd_pcm_msg_send().
> + *
> + * Context: Any context.
> + * Return: 0 on success, -errno on failure.
> + */
> +
> +int virtsnd_pcm_msg_send_locked(struct virtio_pcm_substream *vss, bool single)
> +{
> +	struct virtio_snd_queue *queue;
> +	int rc;
> +	unsigned long flags;
> +
> +	queue = virtsnd_pcm_queue(vss);
> +
> +	spin_lock_irqsave(&queue->lock, flags);
> +	spin_lock(&vss->lock);
> +	rc = virtsnd_pcm_msg_send(vss, single);
> +	spin_unlock(&vss->lock);
> +	spin_unlock_irqrestore(&queue->lock, flags);
> +
> +	return rc;
> +}
> +
>   /**
>    * virtsnd_pcm_msg_pending_num() - Returns the number of pending I/O messages.
>    * @vss: VirtIO substream.
> @@ -320,8 +358,6 @@ static void virtsnd_pcm_msg_complete(struct virtio_pcm_msg *msg,
>   					le32_to_cpu(msg->status.latency_bytes));
>   
>   		schedule_work(&vss->elapsed_period);
> -
> -		virtsnd_pcm_msg_send(vss);
>   	} else if (!vss->msg_count) {
>   		wake_up_all(&vss->msg_empty);
>   	}
> diff --git a/sound/virtio/virtio_pcm_ops.c b/sound/virtio/virtio_pcm_ops.c
> index f8bfb87624be..a208439dbff8 100644
> --- a/sound/virtio/virtio_pcm_ops.c
> +++ b/sound/virtio/virtio_pcm_ops.c
> @@ -238,6 +238,11 @@ static int virtsnd_pcm_hw_params(struct snd_pcm_substream *substream,
>   	 */
>   	virtsnd_pcm_msg_free(vss);
>   
> +	vss->buffer_sz = params_buffer_bytes(hw_params);
> +	vss->buffer = alloc_pages_exact(vss->buffer_sz, GFP_KERNEL);
> +	if (!vss->buffer)
> +		return -ENOMEM;
> +
>   	return virtsnd_pcm_msg_alloc(vss, params_periods(hw_params),
>   				     params_period_bytes(hw_params));
>   }
> @@ -257,6 +262,11 @@ static int virtsnd_pcm_hw_free(struct snd_pcm_substream *substream)
>   	if (!virtsnd_pcm_msg_pending_num(vss))
>   		virtsnd_pcm_msg_free(vss);
>   
> +	if (vss->buffer) {
> +		free_pages_exact(vss->buffer, vss->buffer_sz);
> +		vss->buffer = NULL;
> +	}
> +
>   	return 0;
>   }
>   
> @@ -331,15 +341,18 @@ static int virtsnd_pcm_trigger(struct snd_pcm_substream *substream, int command)
>   	case SNDRV_PCM_TRIGGER_PAUSE_RELEASE:
>   		queue = virtsnd_pcm_queue(vss);
>   
> -		spin_lock_irqsave(&queue->lock, flags);
> -		spin_lock(&vss->lock);
> -		rc = virtsnd_pcm_msg_send(vss);
> -		if (!rc)
> -			vss->xfer_enabled = true;
> -		spin_unlock(&vss->lock);
> -		spin_unlock_irqrestore(&queue->lock, flags);
> -		if (rc)
> -			return rc;
> +		// The buffers should be exposed first during capturing so that
> +		// the device can consume them. Capturing cannot begin
> +		// otherwise.
> +		if (vss->direction == SNDRV_PCM_STREAM_CAPTURE) {
> +			rc = virtsnd_pcm_msg_send_locked(vss, false);
> +			if (rc)
> +				return rc;
> +		}
> +
> +		spin_lock_irqsave(&vss->lock, flags);
> +		vss->xfer_enabled = true;
> +		spin_unlock_irqrestore(&vss->lock, flags);
>   
>   		msg = virtsnd_pcm_ctl_msg_alloc(vss, VIRTIO_SND_R_PCM_START,
>   						GFP_KERNEL);
> @@ -450,8 +463,66 @@ virtsnd_pcm_pointer(struct snd_pcm_substream *substream)
>   	return hw_ptr;
>   }
>   
> -/* PCM substream operators map. */
> -const struct snd_pcm_ops virtsnd_pcm_ops = {
> +static int virtsnd_pcm_pb_copy(struct snd_pcm_substream *substream,
> +			       int channel, unsigned long pos, struct iov_iter
> +			       *src, unsigned long count)
> +{
> +	struct virtio_pcm_substream *vss = snd_pcm_substream_chip(substream);
> +
> +	if (unlikely(pos + count > vss->buffer_sz))
> +		return -EINVAL;
> +
> +	if (copy_from_iter(vss->buffer + pos, count, src) != count)
> +		return -EFAULT;
> +
> +	return virtsnd_pcm_msg_send_locked(vss, true);
> +}
> +
> +static int virtsnd_pcm_cap_copy(struct snd_pcm_substream *substream,
> +				int channel, unsigned long pos, struct iov_iter
> +				*dst, unsigned long count)
> +{
> +	struct virtio_pcm_substream *vss = snd_pcm_substream_chip(substream);
> +
> +	if (unlikely(pos + count > vss->buffer_sz))
> +		return -EINVAL;
> +
> +	if (copy_to_iter(vss->buffer + pos, count, dst) != count)
> +		return -EFAULT;
> +
> +	return virtsnd_pcm_msg_send_locked(vss, true);
> +}
> +
> +static int virtsnd_pcm_pb_silence(struct snd_pcm_substream *substream, int channel,
> +				  unsigned long pos, unsigned long count)
> +{
> +	struct virtio_pcm_substream *vss = snd_pcm_substream_chip(substream);
> +
> +	if (unlikely(pos + count > vss->buffer_sz))
> +		return -EINVAL;
> +
> +	memset(vss->buffer + pos, 0, count);
> +
> +	return virtsnd_pcm_msg_send_locked(vss, true);
> +}
> +
> +/* PCM substream operators map for playback. */
> +const struct snd_pcm_ops virtsnd_pcm_playback_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,
> +	.sync_stop = virtsnd_pcm_sync_stop,
> +	.pointer = virtsnd_pcm_pointer,
> +	.copy = virtsnd_pcm_pb_copy,
> +	.fill_silence = virtsnd_pcm_pb_silence,
> +};
> +
> +/* PCM substream operators map for capturing. */
> +const struct snd_pcm_ops virtsnd_pcm_capture_ops = {
>   	.open = virtsnd_pcm_open,
>   	.close = virtsnd_pcm_close,
>   	.ioctl = snd_pcm_lib_ioctl,
> @@ -461,4 +532,5 @@ const struct snd_pcm_ops virtsnd_pcm_ops = {
>   	.trigger = virtsnd_pcm_trigger,
>   	.sync_stop = virtsnd_pcm_sync_stop,
>   	.pointer = virtsnd_pcm_pointer,
> +	.copy = virtsnd_pcm_cap_copy,
>   };
> 
> base-commit: 8a749fd1a8720d4619c91c8b6e7528c0a355c0aa

-- 
Anton Yakovlev
Senior Software Engineer

OpenSynergy GmbH
Rotherstr. 20, 10245 Berlin

[-- Attachment #2: 0001-ALSA-virtio-use-copy-and-fill_silence-callbacks.patch --]
[-- Type: text/x-diff, Size: 12268 bytes --]

From c9019469c5689d860ee6ea5c4a9ea7caa5009daa Mon Sep 17 00:00:00 2001
From: Matias Ezequiel Vara Larsen <mvaralar@redhat.com>
Date: Tue, 17 Oct 2023 16:34:28 +0900
Subject: [PATCH] ALSA: virtio: use copy and fill_silence callbacks

This commit replaces the mmap mechanism with the copy() and
fill_silence() callbacks for both capturing and playback for the
virtio-sound driver. This change is required to prevent the updating of
the content of a buffer that is already in the available ring.

The current mechanism splits a dma buffer into descriptors that are
exposed to the device. This dma buffer is shared with the user
application. When the device consumes a buffer, the driver moves the
request from the used ring to available ring.

The driver exposes the buffer to the device without knowing if the
content has been updated from the user. The section 2.8.21.1 of the
virtio spec states that: "The device MAY access the descriptor chains
the driver created and the memory they refer to immediately". If the
device picks up buffers from the available ring just after it is
notified, it happens that the content may be old.

By providing the copy() callback, the driver first updates the content
of the buffer, and then, exposes the buffer to the device by enqueuing
it in the available ring. Thus, device always picks up a buffer that is
updated.

For capturing, the driver starts by exposing all the available buffers
to device. After device updates the content of a buffer, it enqueues it
in the used ring. It is only after the copy() for capturing is issued
that the driver re-enqueues the buffer in the available ring.

Note that the copy() function assumes that user is always writing a
period. Testing shows that this is true but I may be wrong. This RFC
aims at clarifying this.

Signed-off-by: Matias Ezequiel Vara Larsen <mvaralar@redhat.com>
---
 sound/virtio/virtio_pcm.c     |  7 ++-
 sound/virtio/virtio_pcm.h     |  9 ++--
 sound/virtio/virtio_pcm_msg.c | 87 +++++++++++++++++++++++------------
 sound/virtio/virtio_pcm_ops.c | 81 ++++++++++++++++++++++++++------
 4 files changed, 135 insertions(+), 49 deletions(-)

diff --git a/sound/virtio/virtio_pcm.c b/sound/virtio/virtio_pcm.c
index c10d91fff2fb..66d67eef1bcc 100644
--- a/sound/virtio/virtio_pcm.c
+++ b/sound/virtio/virtio_pcm.c
@@ -104,12 +104,11 @@ static int virtsnd_pcm_build_hw(struct virtio_pcm_substream *vss,
 	 * only message-based transport.
 	 */
 	vss->hw.info =
-		SNDRV_PCM_INFO_MMAP |
-		SNDRV_PCM_INFO_MMAP_VALID |
 		SNDRV_PCM_INFO_BATCH |
 		SNDRV_PCM_INFO_BLOCK_TRANSFER |
 		SNDRV_PCM_INFO_INTERLEAVED |
-		SNDRV_PCM_INFO_PAUSE;
+		SNDRV_PCM_INFO_PAUSE |
+		SNDRV_PCM_INFO_NO_REWINDS;
 
 	if (!info->channels_min || info->channels_min > info->channels_max) {
 		dev_err(&vdev->dev,
@@ -471,7 +470,7 @@ int virtsnd_pcm_build_devs(struct virtio_snd *snd)
 			for (kss = ks->substream; kss; kss = kss->next)
 				vs->substreams[kss->number]->substream = kss;
 
-			snd_pcm_set_ops(vpcm->pcm, i, &virtsnd_pcm_ops);
+			snd_pcm_set_ops(vpcm->pcm, i, &virtsnd_pcm_ops[i]);
 		}
 
 		snd_pcm_set_managed_buffer_all(vpcm->pcm,
diff --git a/sound/virtio/virtio_pcm.h b/sound/virtio/virtio_pcm.h
index 062eb8e8f2cf..8b42928a8e01 100644
--- a/sound/virtio/virtio_pcm.h
+++ b/sound/virtio/virtio_pcm.h
@@ -57,7 +57,6 @@ struct virtio_pcm_substream {
 	bool suspended;
 	struct virtio_pcm_msg **msgs;
 	unsigned int nmsgs;
-	int msg_last_enqueued;
 	unsigned int msg_count;
 	wait_queue_head_t msg_empty;
 };
@@ -90,7 +89,7 @@ struct virtio_pcm {
 	struct virtio_pcm_stream streams[SNDRV_PCM_STREAM_LAST + 1];
 };
 
-extern const struct snd_pcm_ops virtsnd_pcm_ops;
+extern const struct snd_pcm_ops virtsnd_pcm_ops[];
 
 int virtsnd_pcm_validate(struct virtio_device *vdev);
 
@@ -117,7 +116,11 @@ int virtsnd_pcm_msg_alloc(struct virtio_pcm_substream *vss,
 
 void virtsnd_pcm_msg_free(struct virtio_pcm_substream *vss);
 
-int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss);
+int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss, unsigned long offset,
+			 unsigned long bytes);
+
+int virtsnd_pcm_msg_send_locked(struct virtio_pcm_substream *vss,
+				unsigned long offset, unsigned long bytes);
 
 unsigned int virtsnd_pcm_msg_pending_num(struct virtio_pcm_substream *vss);
 
diff --git a/sound/virtio/virtio_pcm_msg.c b/sound/virtio/virtio_pcm_msg.c
index aca2dc1989ba..3bc0a61a046d 100644
--- a/sound/virtio/virtio_pcm_msg.c
+++ b/sound/virtio/virtio_pcm_msg.c
@@ -155,7 +155,6 @@ int virtsnd_pcm_msg_alloc(struct virtio_pcm_substream *vss,
 			    sizeof(msg->xfer));
 		sg_init_one(&msg->sgs[PCM_MSG_SG_STATUS], &msg->status,
 			    sizeof(msg->status));
-		msg->length = period_bytes;
 		virtsnd_pcm_sg_from(&msg->sgs[PCM_MSG_SG_DATA], sg_num, data,
 				    period_bytes);
 
@@ -198,49 +197,63 @@ void virtsnd_pcm_msg_free(struct virtio_pcm_substream *vss)
  *          spinlocks to be held by caller.
  * Return: 0 on success, -errno on failure.
  */
-int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss)
+int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss, unsigned long offset,
+			 unsigned long bytes)
 {
-	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;
+	unsigned long period_bytes = snd_pcm_lib_period_bytes(vss->substream);
+	unsigned long start, end, i;
+	unsigned int msg_count = vss->msg_count;
 	bool notify = false;
+	int rc;
 
-	i = (vss->msg_last_enqueued + 1) % runtime->periods;
-	n = runtime->periods - vss->msg_count;
+	start = offset / period_bytes;
+	end = (offset + bytes - 1) / period_bytes;
 
-	for (; n; --n, i = (i + 1) % runtime->periods) {
+	for (i = start; i <= end; i++) {
 		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;
+		unsigned long n;
+
+		n = period_bytes - (offset % period_bytes);
+		if (n > bytes)
+			n = bytes;
+
+		msg->length += n;
+		if (msg->length == period_bytes) {
+			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_count++;
 		}
 
-		vss->msg_last_enqueued = i;
-		vss->msg_count++;
+		offset = 0;
+		bytes -= n;
 	}
 
+	if (msg_count == vss->msg_count)
+		return 0;
+
 	if (!(vss->features & (1U << VIRTIO_SND_PCM_F_MSG_POLLING)))
 		notify = virtqueue_kick_prepare(vqueue);
 
@@ -250,6 +263,22 @@ int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss)
 	return 0;
 }
 
+int virtsnd_pcm_msg_send_locked(struct virtio_pcm_substream *vss,
+				unsigned long offset, unsigned long bytes)
+{
+	struct virtio_snd_queue *queue = virtsnd_pcm_queue(vss);
+	unsigned long flags;
+	int rc;
+
+	spin_lock_irqsave(&queue->lock, flags);
+	spin_lock(&vss->lock);
+	rc = virtsnd_pcm_msg_send(vss, offset, bytes);
+	spin_unlock(&vss->lock);
+	spin_unlock_irqrestore(&queue->lock, flags);
+
+	return rc;
+}
+
 /**
  * virtsnd_pcm_msg_pending_num() - Returns the number of pending I/O messages.
  * @vss: VirtIO substream.
@@ -309,6 +338,8 @@ static void virtsnd_pcm_msg_complete(struct virtio_pcm_msg *msg,
 	if (vss->hw_ptr >= vss->buffer_bytes)
 		vss->hw_ptr -= vss->buffer_bytes;
 
+	msg->length = 0;
+
 	vss->xfer_xrun = false;
 	vss->msg_count--;
 
@@ -320,8 +351,6 @@ static void virtsnd_pcm_msg_complete(struct virtio_pcm_msg *msg,
 					le32_to_cpu(msg->status.latency_bytes));
 
 		schedule_work(&vss->elapsed_period);
-
-		virtsnd_pcm_msg_send(vss);
 	} else if (!vss->msg_count) {
 		wake_up_all(&vss->msg_empty);
 	}
diff --git a/sound/virtio/virtio_pcm_ops.c b/sound/virtio/virtio_pcm_ops.c
index f8bfb87624be..4569b285f520 100644
--- a/sound/virtio/virtio_pcm_ops.c
+++ b/sound/virtio/virtio_pcm_ops.c
@@ -282,7 +282,6 @@ static int virtsnd_pcm_prepare(struct snd_pcm_substream *substream)
 
 		vss->buffer_bytes = snd_pcm_lib_buffer_bytes(substream);
 		vss->hw_ptr = 0;
-		vss->msg_last_enqueued = -1;
 	} else {
 		struct snd_pcm_runtime *runtime = substream->runtime;
 		unsigned int buffer_bytes = snd_pcm_lib_buffer_bytes(substream);
@@ -324,7 +323,7 @@ static int virtsnd_pcm_trigger(struct snd_pcm_substream *substream, int command)
 	struct virtio_snd_queue *queue;
 	struct virtio_snd_msg *msg;
 	unsigned long flags;
-	int rc;
+	int rc = 0;
 
 	switch (command) {
 	case SNDRV_PCM_TRIGGER_START:
@@ -333,7 +332,8 @@ static int virtsnd_pcm_trigger(struct snd_pcm_substream *substream, int command)
 
 		spin_lock_irqsave(&queue->lock, flags);
 		spin_lock(&vss->lock);
-		rc = virtsnd_pcm_msg_send(vss);
+		if (vss->direction == SNDRV_PCM_STREAM_CAPTURE)
+			rc = virtsnd_pcm_msg_send(vss, 0, vss->buffer_bytes);
 		if (!rc)
 			vss->xfer_enabled = true;
 		spin_unlock(&vss->lock);
@@ -450,15 +450,70 @@ virtsnd_pcm_pointer(struct snd_pcm_substream *substream)
 	return hw_ptr;
 }
 
+static int virtsnd_pcm_pb_silence(struct snd_pcm_substream *substream,
+				  int channel, unsigned long pos,
+				  unsigned long bytes)
+{
+	struct virtio_pcm_substream *vss = snd_pcm_substream_chip(substream);
+	struct snd_pcm_runtime *runtime = substream->runtime;
+
+	snd_pcm_format_set_silence(runtime->format, runtime->dma_area + pos,
+				   bytes_to_samples(runtime, bytes));
+
+	return virtsnd_pcm_msg_send_locked(vss, pos, bytes);
+}
+
+static int virtsnd_pcm_pb_copy(struct snd_pcm_substream *substream, int channel,
+			       unsigned long pos, struct iov_iter *iter,
+			       unsigned long bytes)
+{
+	struct virtio_pcm_substream *vss = snd_pcm_substream_chip(substream);
+	struct snd_pcm_runtime *runtime = substream->runtime;
+
+	if (copy_from_iter(runtime->dma_area + pos, bytes, iter) != bytes)
+		return -EFAULT;
+
+	return virtsnd_pcm_msg_send_locked(vss, pos, bytes);
+}
+
+static int virtsnd_pcm_cp_copy(struct snd_pcm_substream *substream, int channel,
+			       unsigned long pos, struct iov_iter *iter,
+			       unsigned long bytes)
+{
+	struct virtio_pcm_substream *vss = snd_pcm_substream_chip(substream);
+	struct snd_pcm_runtime *runtime = substream->runtime;
+
+	if (copy_to_iter(runtime->dma_area + pos, bytes, iter) != bytes)
+		return -EFAULT;
+
+	return virtsnd_pcm_msg_send_locked(vss, pos, bytes);
+}
+
 /* 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,
-	.sync_stop = virtsnd_pcm_sync_stop,
-	.pointer = virtsnd_pcm_pointer,
+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,
+		.sync_stop = virtsnd_pcm_sync_stop,
+		.pointer = virtsnd_pcm_pointer,
+		.copy = virtsnd_pcm_pb_copy,
+		.fill_silence = virtsnd_pcm_pb_silence,
+	},
+	{
+		.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,
+		.sync_stop = virtsnd_pcm_sync_stop,
+		.pointer = virtsnd_pcm_pointer,
+		.copy = virtsnd_pcm_cp_copy,
+	},
 };
-- 
2.42.0

Re: [RFC PATCH] ALSA: virtio: use copy and fill_silence callbacks

[Matias Ezequiel Vara Larsen]

Hello Anton, 

Thanks for your help! I am going to send a second version of the patch
with your changes. Is it OK if I add you with the "Co-developed-by"
tag?.

Matias

On Tue, Oct 17, 2023 at 05:11:30PM +0900, Anton Yakovlev wrote:
> Hi Matias,
> 
> Thanks for your help! I updated and corrected your patch a little bit (see
> attachment). All changes were tested, there were no problems on my side.
> 
> See also a few inline comments.
> 
> 
> 
> On 13.10.2023 00:10, Matias Ezequiel Vara Larsen wrote:
> > This commit replaces the mmap mechanism with the copy() and
> > fill_silence() callbacks for both capturing and playback for the
> > virtio-sound driver. This change is required to prevent the updating of
> > the content of a buffer that is already in the available ring.
> > 
> > The current mechanism splits a dma buffer into descriptors that are
> > exposed to the device. This dma buffer is shared with the user
> > application. When the device consumes a buffer, the driver moves the
> > request from the used ring to available ring.
> > 
> > The driver exposes the buffer to the device without knowing if the
> > content has been updated from the user. The section 2.8.21.1 of the
> > virtio spec states that: "The device MAY access the descriptor chains
> > the driver created and the memory they refer to immediately". If the
> > device picks up buffers from the available ring just after it is
> > notified, it happens that the content may be old.
> > 
> > By providing the copy() callback, the driver first updates the content
> > of the buffer, and then, exposes the buffer to the device by enqueuing
> > it in the available ring. Thus, device always picks up a buffer that is
> > updated.
> > 
> > For capturing, the driver starts by exposing all the available buffers
> > to device. After device updates the content of a buffer, it enqueues it
> > in the used ring. It is only after the copy() for capturing is issued
> > that the driver re-enqueues the buffer in the available ring.
> > 
> > Note that the copy() function assumes that user is always writing a
> > period. Testing shows that this is true but I may be wrong. This RFC
> > aims at clarifying this.
> > 
> > Signed-off-by: Matias Ezequiel Vara Larsen <mvaralar@redhat.com>
> > ---
> >   sound/virtio/virtio_pcm.c     | 11 ++--
> >   sound/virtio/virtio_pcm.h     |  9 +++-
> >   sound/virtio/virtio_pcm_msg.c | 50 ++++++++++++++++---
> >   sound/virtio/virtio_pcm_ops.c | 94 +++++++++++++++++++++++++++++++----
> >   4 files changed, 137 insertions(+), 27 deletions(-)
> > 
> > diff --git a/sound/virtio/virtio_pcm.c b/sound/virtio/virtio_pcm.c
> > index c10d91fff2fb..bfe982952303 100644
> > --- a/sound/virtio/virtio_pcm.c
> > +++ b/sound/virtio/virtio_pcm.c
> > @@ -104,8 +104,6 @@ static int virtsnd_pcm_build_hw(struct virtio_pcm_substream *vss,
> >   	 * only message-based transport.
> >   	 */
> >   	vss->hw.info =
> > -		SNDRV_PCM_INFO_MMAP |
> > -		SNDRV_PCM_INFO_MMAP_VALID |
> >   		SNDRV_PCM_INFO_BATCH |
> >   		SNDRV_PCM_INFO_BLOCK_TRANSFER |
> >   		SNDRV_PCM_INFO_INTERLEAVED |
> 
> We need also necessary to disable rewinds, since now only sequential
> reading/writing of frames is supported.
> 
> 
> > @@ -471,12 +469,11 @@ int virtsnd_pcm_build_devs(struct virtio_snd *snd)
> >   			for (kss = ks->substream; kss; kss = kss->next)
> >   				vs->substreams[kss->number]->substream = kss;
> > -			snd_pcm_set_ops(vpcm->pcm, i, &virtsnd_pcm_ops);
> > +			if (i == SNDRV_PCM_STREAM_CAPTURE)
> > +				snd_pcm_set_ops(vpcm->pcm, i, &virtsnd_pcm_capture_ops);
> > +			else
> > +				snd_pcm_set_ops(vpcm->pcm, i, &virtsnd_pcm_playback_ops);
> >   		}
> > -
> > -		snd_pcm_set_managed_buffer_all(vpcm->pcm,
> > -					       SNDRV_DMA_TYPE_VMALLOC, NULL,
> > -					       0, 0);
> 
> It is not right. Buffer allocation/freeing is controlled by the kernel
> subsystem, so the driver doesn't have to worry about it.
> 
> 
> >   	}
> >   	return 0;
> > diff --git a/sound/virtio/virtio_pcm.h b/sound/virtio/virtio_pcm.h
> > index 062eb8e8f2cf..1c1106ec971f 100644
> > --- a/sound/virtio/virtio_pcm.h
> > +++ b/sound/virtio/virtio_pcm.h
> > @@ -50,6 +50,8 @@ struct virtio_pcm_substream {
> >   	struct work_struct elapsed_period;
> >   	spinlock_t lock;
> >   	size_t buffer_bytes;
> > +	u8 *buffer;
> > +	size_t buffer_sz;
> >   	size_t hw_ptr;
> >   	bool xfer_enabled;
> >   	bool xfer_xrun;
> > @@ -90,7 +92,8 @@ struct virtio_pcm {
> >   	struct virtio_pcm_stream streams[SNDRV_PCM_STREAM_LAST + 1];
> >   };
> > -extern const struct snd_pcm_ops virtsnd_pcm_ops;
> > +extern const struct snd_pcm_ops virtsnd_pcm_playback_ops;
> > +extern const struct snd_pcm_ops virtsnd_pcm_capture_ops;
> >   int virtsnd_pcm_validate(struct virtio_device *vdev);
> > @@ -117,7 +120,9 @@ int virtsnd_pcm_msg_alloc(struct virtio_pcm_substream *vss,
> >   void virtsnd_pcm_msg_free(struct virtio_pcm_substream *vss);
> > -int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss);
> > +int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss, bool single);
> > +
> > +int virtsnd_pcm_msg_send_locked(struct virtio_pcm_substream *vss, bool single);
> >   unsigned int virtsnd_pcm_msg_pending_num(struct virtio_pcm_substream *vss);
> > diff --git a/sound/virtio/virtio_pcm_msg.c b/sound/virtio/virtio_pcm_msg.c
> > index aca2dc1989ba..9a5f9814cb62 100644
> > --- a/sound/virtio/virtio_pcm_msg.c
> > +++ b/sound/virtio/virtio_pcm_msg.c
> > @@ -132,7 +132,6 @@ static void virtsnd_pcm_sg_from(struct scatterlist *sgs, int nsgs, u8 *data,
> >   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;
> >   	vss->msgs = kcalloc(periods, sizeof(*vss->msgs), GFP_KERNEL);
> > @@ -142,7 +141,7 @@ int virtsnd_pcm_msg_alloc(struct virtio_pcm_substream *vss,
> >   	vss->nmsgs = periods;
> >   	for (i = 0; i < periods; ++i) {
> > -		u8 *data = runtime->dma_area + period_bytes * i;
> > +		u8 *data = vss->buffer + period_bytes * i;
> >   		int sg_num = virtsnd_pcm_sg_num(data, period_bytes);
> >   		struct virtio_pcm_msg *msg;
> > @@ -186,10 +185,12 @@ void virtsnd_pcm_msg_free(struct virtio_pcm_substream *vss)
> >   /**
> >    * virtsnd_pcm_msg_send() - Send asynchronous I/O messages.
> >    * @vss: VirtIO PCM substream.
> > + * @single: true to enqueue a single message, false to enqueue all of them.
> >    *
> >    * 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:
> > + * function is called, first non-enqueued message is added to the virtqueue.
> > + * When single is True, only the first message is enqueued. When False, all the
> > + * available messages are enqueued.  The function keeps track of two values:
> >    *
> >    *   msg_last_enqueued = index of the last enqueued message,
> >    *   msg_count = # of pending messages in the virtqueue.
> > @@ -198,7 +199,7 @@ void virtsnd_pcm_msg_free(struct virtio_pcm_substream *vss)
> >    *          spinlocks to be held by caller.
> >    * Return: 0 on success, -errno on failure.
> >    */
> > -int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss)
> > +int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss, bool single)
> 
> I would propose to make this function more generic, specifing the offset and
> size for the modified part of the buffer. This way no assumptions need to be
> made. We can also guarantee that we only put fully written/read messages into
> the virtqueue.
> 
> 
> 
> >   {
> >   	struct snd_pcm_runtime *runtime = vss->substream->runtime;
> >   	struct virtio_snd *snd = vss->snd;
> > @@ -211,6 +212,13 @@ int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss)
> >   	i = (vss->msg_last_enqueued + 1) % runtime->periods;
> >   	n = runtime->periods - vss->msg_count;
> > +	if (single) {
> > +		if (n < 1)
> > +			return -EFAULT;
> > +
> > +		n = 1;
> > +	}
> > +
> >   	for (; n; --n, i = (i + 1) % runtime->periods) {
> >   		struct virtio_pcm_msg *msg = vss->msgs[i];
> >   		struct scatterlist *psgs[] = {
> > @@ -250,6 +258,36 @@ int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss)
> >   	return 0;
> >   }
> > +/**
> > + * virtsnd_pcm_msg_send_locked() - Send asynchronous I/O messages.
> > + * @vss: VirtIO PCM substream.
> > + * @single: true to enqueue a single message, false to enqueue all of them.
> > + *
> > + * This function holds the tx/rx queue and the VirtIO substream spinlocks
> > + * before calling virtsnd_pcm_msg_send(). This is a wrapper function to ease
> > + * the invocation of virtsnd_pcm_msg_send().
> > + *
> > + * Context: Any context.
> > + * Return: 0 on success, -errno on failure.
> > + */
> > +
> > +int virtsnd_pcm_msg_send_locked(struct virtio_pcm_substream *vss, bool single)
> > +{
> > +	struct virtio_snd_queue *queue;
> > +	int rc;
> > +	unsigned long flags;
> > +
> > +	queue = virtsnd_pcm_queue(vss);
> > +
> > +	spin_lock_irqsave(&queue->lock, flags);
> > +	spin_lock(&vss->lock);
> > +	rc = virtsnd_pcm_msg_send(vss, single);
> > +	spin_unlock(&vss->lock);
> > +	spin_unlock_irqrestore(&queue->lock, flags);
> > +
> > +	return rc;
> > +}
> > +
> >   /**
> >    * virtsnd_pcm_msg_pending_num() - Returns the number of pending I/O messages.
> >    * @vss: VirtIO substream.
> > @@ -320,8 +358,6 @@ static void virtsnd_pcm_msg_complete(struct virtio_pcm_msg *msg,
> >   					le32_to_cpu(msg->status.latency_bytes));
> >   		schedule_work(&vss->elapsed_period);
> > -
> > -		virtsnd_pcm_msg_send(vss);
> >   	} else if (!vss->msg_count) {
> >   		wake_up_all(&vss->msg_empty);
> >   	}
> > diff --git a/sound/virtio/virtio_pcm_ops.c b/sound/virtio/virtio_pcm_ops.c
> > index f8bfb87624be..a208439dbff8 100644
> > --- a/sound/virtio/virtio_pcm_ops.c
> > +++ b/sound/virtio/virtio_pcm_ops.c
> > @@ -238,6 +238,11 @@ static int virtsnd_pcm_hw_params(struct snd_pcm_substream *substream,
> >   	 */
> >   	virtsnd_pcm_msg_free(vss);
> > +	vss->buffer_sz = params_buffer_bytes(hw_params);
> > +	vss->buffer = alloc_pages_exact(vss->buffer_sz, GFP_KERNEL);
> > +	if (!vss->buffer)
> > +		return -ENOMEM;
> > +
> >   	return virtsnd_pcm_msg_alloc(vss, params_periods(hw_params),
> >   				     params_period_bytes(hw_params));
> >   }
> > @@ -257,6 +262,11 @@ static int virtsnd_pcm_hw_free(struct snd_pcm_substream *substream)
> >   	if (!virtsnd_pcm_msg_pending_num(vss))
> >   		virtsnd_pcm_msg_free(vss);
> > +	if (vss->buffer) {
> > +		free_pages_exact(vss->buffer, vss->buffer_sz);
> > +		vss->buffer = NULL;
> > +	}
> > +
> >   	return 0;
> >   }
> > @@ -331,15 +341,18 @@ static int virtsnd_pcm_trigger(struct snd_pcm_substream *substream, int command)
> >   	case SNDRV_PCM_TRIGGER_PAUSE_RELEASE:
> >   		queue = virtsnd_pcm_queue(vss);
> > -		spin_lock_irqsave(&queue->lock, flags);
> > -		spin_lock(&vss->lock);
> > -		rc = virtsnd_pcm_msg_send(vss);
> > -		if (!rc)
> > -			vss->xfer_enabled = true;
> > -		spin_unlock(&vss->lock);
> > -		spin_unlock_irqrestore(&queue->lock, flags);
> > -		if (rc)
> > -			return rc;
> > +		// The buffers should be exposed first during capturing so that
> > +		// the device can consume them. Capturing cannot begin
> > +		// otherwise.
> > +		if (vss->direction == SNDRV_PCM_STREAM_CAPTURE) {
> > +			rc = virtsnd_pcm_msg_send_locked(vss, false);
> > +			if (rc)
> > +				return rc;
> > +		}
> > +
> > +		spin_lock_irqsave(&vss->lock, flags);
> > +		vss->xfer_enabled = true;
> > +		spin_unlock_irqrestore(&vss->lock, flags);
> >   		msg = virtsnd_pcm_ctl_msg_alloc(vss, VIRTIO_SND_R_PCM_START,
> >   						GFP_KERNEL);
> > @@ -450,8 +463,66 @@ virtsnd_pcm_pointer(struct snd_pcm_substream *substream)
> >   	return hw_ptr;
> >   }
> > -/* PCM substream operators map. */
> > -const struct snd_pcm_ops virtsnd_pcm_ops = {
> > +static int virtsnd_pcm_pb_copy(struct snd_pcm_substream *substream,
> > +			       int channel, unsigned long pos, struct iov_iter
> > +			       *src, unsigned long count)
> > +{
> > +	struct virtio_pcm_substream *vss = snd_pcm_substream_chip(substream);
> > +
> > +	if (unlikely(pos + count > vss->buffer_sz))
> > +		return -EINVAL;
> > +
> > +	if (copy_from_iter(vss->buffer + pos, count, src) != count)
> > +		return -EFAULT;
> > +
> > +	return virtsnd_pcm_msg_send_locked(vss, true);
> > +}
> > +
> > +static int virtsnd_pcm_cap_copy(struct snd_pcm_substream *substream,
> > +				int channel, unsigned long pos, struct iov_iter
> > +				*dst, unsigned long count)
> > +{
> > +	struct virtio_pcm_substream *vss = snd_pcm_substream_chip(substream);
> > +
> > +	if (unlikely(pos + count > vss->buffer_sz))
> > +		return -EINVAL;
> > +
> > +	if (copy_to_iter(vss->buffer + pos, count, dst) != count)
> > +		return -EFAULT;
> > +
> > +	return virtsnd_pcm_msg_send_locked(vss, true);
> > +}
> > +
> > +static int virtsnd_pcm_pb_silence(struct snd_pcm_substream *substream, int channel,
> > +				  unsigned long pos, unsigned long count)
> > +{
> > +	struct virtio_pcm_substream *vss = snd_pcm_substream_chip(substream);
> > +
> > +	if (unlikely(pos + count > vss->buffer_sz))
> > +		return -EINVAL;
> > +
> > +	memset(vss->buffer + pos, 0, count);
> > +
> > +	return virtsnd_pcm_msg_send_locked(vss, true);
> > +}
> > +
> > +/* PCM substream operators map for playback. */
> > +const struct snd_pcm_ops virtsnd_pcm_playback_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,
> > +	.sync_stop = virtsnd_pcm_sync_stop,
> > +	.pointer = virtsnd_pcm_pointer,
> > +	.copy = virtsnd_pcm_pb_copy,
> > +	.fill_silence = virtsnd_pcm_pb_silence,
> > +};
> > +
> > +/* PCM substream operators map for capturing. */
> > +const struct snd_pcm_ops virtsnd_pcm_capture_ops = {
> >   	.open = virtsnd_pcm_open,
> >   	.close = virtsnd_pcm_close,
> >   	.ioctl = snd_pcm_lib_ioctl,
> > @@ -461,4 +532,5 @@ const struct snd_pcm_ops virtsnd_pcm_ops = {
> >   	.trigger = virtsnd_pcm_trigger,
> >   	.sync_stop = virtsnd_pcm_sync_stop,
> >   	.pointer = virtsnd_pcm_pointer,
> > +	.copy = virtsnd_pcm_cap_copy,
> >   };
> > 
> > base-commit: 8a749fd1a8720d4619c91c8b6e7528c0a355c0aa
> 
> -- 
> Anton Yakovlev
> Senior Software Engineer
> 
> OpenSynergy GmbH
> Rotherstr. 20, 10245 Berlin

> From c9019469c5689d860ee6ea5c4a9ea7caa5009daa Mon Sep 17 00:00:00 2001
> From: Matias Ezequiel Vara Larsen <mvaralar@redhat.com>
> Date: Tue, 17 Oct 2023 16:34:28 +0900
> Subject: [PATCH] ALSA: virtio: use copy and fill_silence callbacks
> 
> This commit replaces the mmap mechanism with the copy() and
> fill_silence() callbacks for both capturing and playback for the
> virtio-sound driver. This change is required to prevent the updating of
> the content of a buffer that is already in the available ring.
> 
> The current mechanism splits a dma buffer into descriptors that are
> exposed to the device. This dma buffer is shared with the user
> application. When the device consumes a buffer, the driver moves the
> request from the used ring to available ring.
> 
> The driver exposes the buffer to the device without knowing if the
> content has been updated from the user. The section 2.8.21.1 of the
> virtio spec states that: "The device MAY access the descriptor chains
> the driver created and the memory they refer to immediately". If the
> device picks up buffers from the available ring just after it is
> notified, it happens that the content may be old.
> 
> By providing the copy() callback, the driver first updates the content
> of the buffer, and then, exposes the buffer to the device by enqueuing
> it in the available ring. Thus, device always picks up a buffer that is
> updated.
> 
> For capturing, the driver starts by exposing all the available buffers
> to device. After device updates the content of a buffer, it enqueues it
> in the used ring. It is only after the copy() for capturing is issued
> that the driver re-enqueues the buffer in the available ring.
> 
> Note that the copy() function assumes that user is always writing a
> period. Testing shows that this is true but I may be wrong. This RFC
> aims at clarifying this.
> 
> Signed-off-by: Matias Ezequiel Vara Larsen <mvaralar@redhat.com>
> ---
>  sound/virtio/virtio_pcm.c     |  7 ++-
>  sound/virtio/virtio_pcm.h     |  9 ++--
>  sound/virtio/virtio_pcm_msg.c | 87 +++++++++++++++++++++++------------
>  sound/virtio/virtio_pcm_ops.c | 81 ++++++++++++++++++++++++++------
>  4 files changed, 135 insertions(+), 49 deletions(-)
> 
> diff --git a/sound/virtio/virtio_pcm.c b/sound/virtio/virtio_pcm.c
> index c10d91fff2fb..66d67eef1bcc 100644
> --- a/sound/virtio/virtio_pcm.c
> +++ b/sound/virtio/virtio_pcm.c
> @@ -104,12 +104,11 @@ static int virtsnd_pcm_build_hw(struct virtio_pcm_substream *vss,
>  	 * only message-based transport.
>  	 */
>  	vss->hw.info =
> -		SNDRV_PCM_INFO_MMAP |
> -		SNDRV_PCM_INFO_MMAP_VALID |
>  		SNDRV_PCM_INFO_BATCH |
>  		SNDRV_PCM_INFO_BLOCK_TRANSFER |
>  		SNDRV_PCM_INFO_INTERLEAVED |
> -		SNDRV_PCM_INFO_PAUSE;
> +		SNDRV_PCM_INFO_PAUSE |
> +		SNDRV_PCM_INFO_NO_REWINDS;
>  
>  	if (!info->channels_min || info->channels_min > info->channels_max) {
>  		dev_err(&vdev->dev,
> @@ -471,7 +470,7 @@ int virtsnd_pcm_build_devs(struct virtio_snd *snd)
>  			for (kss = ks->substream; kss; kss = kss->next)
>  				vs->substreams[kss->number]->substream = kss;
>  
> -			snd_pcm_set_ops(vpcm->pcm, i, &virtsnd_pcm_ops);
> +			snd_pcm_set_ops(vpcm->pcm, i, &virtsnd_pcm_ops[i]);
>  		}
>  
>  		snd_pcm_set_managed_buffer_all(vpcm->pcm,
> diff --git a/sound/virtio/virtio_pcm.h b/sound/virtio/virtio_pcm.h
> index 062eb8e8f2cf..8b42928a8e01 100644
> --- a/sound/virtio/virtio_pcm.h
> +++ b/sound/virtio/virtio_pcm.h
> @@ -57,7 +57,6 @@ struct virtio_pcm_substream {
>  	bool suspended;
>  	struct virtio_pcm_msg **msgs;
>  	unsigned int nmsgs;
> -	int msg_last_enqueued;
>  	unsigned int msg_count;
>  	wait_queue_head_t msg_empty;
>  };
> @@ -90,7 +89,7 @@ struct virtio_pcm {
>  	struct virtio_pcm_stream streams[SNDRV_PCM_STREAM_LAST + 1];
>  };
>  
> -extern const struct snd_pcm_ops virtsnd_pcm_ops;
> +extern const struct snd_pcm_ops virtsnd_pcm_ops[];
>  
>  int virtsnd_pcm_validate(struct virtio_device *vdev);
>  
> @@ -117,7 +116,11 @@ int virtsnd_pcm_msg_alloc(struct virtio_pcm_substream *vss,
>  
>  void virtsnd_pcm_msg_free(struct virtio_pcm_substream *vss);
>  
> -int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss);
> +int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss, unsigned long offset,
> +			 unsigned long bytes);
> +
> +int virtsnd_pcm_msg_send_locked(struct virtio_pcm_substream *vss,
> +				unsigned long offset, unsigned long bytes);
>  
>  unsigned int virtsnd_pcm_msg_pending_num(struct virtio_pcm_substream *vss);
>  
> diff --git a/sound/virtio/virtio_pcm_msg.c b/sound/virtio/virtio_pcm_msg.c
> index aca2dc1989ba..3bc0a61a046d 100644
> --- a/sound/virtio/virtio_pcm_msg.c
> +++ b/sound/virtio/virtio_pcm_msg.c
> @@ -155,7 +155,6 @@ int virtsnd_pcm_msg_alloc(struct virtio_pcm_substream *vss,
>  			    sizeof(msg->xfer));
>  		sg_init_one(&msg->sgs[PCM_MSG_SG_STATUS], &msg->status,
>  			    sizeof(msg->status));
> -		msg->length = period_bytes;
>  		virtsnd_pcm_sg_from(&msg->sgs[PCM_MSG_SG_DATA], sg_num, data,
>  				    period_bytes);
>  
> @@ -198,49 +197,63 @@ void virtsnd_pcm_msg_free(struct virtio_pcm_substream *vss)
>   *          spinlocks to be held by caller.
>   * Return: 0 on success, -errno on failure.
>   */
> -int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss)
> +int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss, unsigned long offset,
> +			 unsigned long bytes)
>  {
> -	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;
> +	unsigned long period_bytes = snd_pcm_lib_period_bytes(vss->substream);
> +	unsigned long start, end, i;
> +	unsigned int msg_count = vss->msg_count;
>  	bool notify = false;
> +	int rc;
>  
> -	i = (vss->msg_last_enqueued + 1) % runtime->periods;
> -	n = runtime->periods - vss->msg_count;
> +	start = offset / period_bytes;
> +	end = (offset + bytes - 1) / period_bytes;
>  
> -	for (; n; --n, i = (i + 1) % runtime->periods) {
> +	for (i = start; i <= end; i++) {
>  		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;
> +		unsigned long n;
> +
> +		n = period_bytes - (offset % period_bytes);
> +		if (n > bytes)
> +			n = bytes;
> +
> +		msg->length += n;
> +		if (msg->length == period_bytes) {
> +			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_count++;
>  		}
>  
> -		vss->msg_last_enqueued = i;
> -		vss->msg_count++;
> +		offset = 0;
> +		bytes -= n;
>  	}
>  
> +	if (msg_count == vss->msg_count)
> +		return 0;
> +
>  	if (!(vss->features & (1U << VIRTIO_SND_PCM_F_MSG_POLLING)))
>  		notify = virtqueue_kick_prepare(vqueue);
>  
> @@ -250,6 +263,22 @@ int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss)
>  	return 0;
>  }
>  
> +int virtsnd_pcm_msg_send_locked(struct virtio_pcm_substream *vss,
> +				unsigned long offset, unsigned long bytes)
> +{
> +	struct virtio_snd_queue *queue = virtsnd_pcm_queue(vss);
> +	unsigned long flags;
> +	int rc;
> +
> +	spin_lock_irqsave(&queue->lock, flags);
> +	spin_lock(&vss->lock);
> +	rc = virtsnd_pcm_msg_send(vss, offset, bytes);
> +	spin_unlock(&vss->lock);
> +	spin_unlock_irqrestore(&queue->lock, flags);
> +
> +	return rc;
> +}
> +
>  /**
>   * virtsnd_pcm_msg_pending_num() - Returns the number of pending I/O messages.
>   * @vss: VirtIO substream.
> @@ -309,6 +338,8 @@ static void virtsnd_pcm_msg_complete(struct virtio_pcm_msg *msg,
>  	if (vss->hw_ptr >= vss->buffer_bytes)
>  		vss->hw_ptr -= vss->buffer_bytes;
>  
> +	msg->length = 0;
> +
>  	vss->xfer_xrun = false;
>  	vss->msg_count--;
>  
> @@ -320,8 +351,6 @@ static void virtsnd_pcm_msg_complete(struct virtio_pcm_msg *msg,
>  					le32_to_cpu(msg->status.latency_bytes));
>  
>  		schedule_work(&vss->elapsed_period);
> -
> -		virtsnd_pcm_msg_send(vss);
>  	} else if (!vss->msg_count) {
>  		wake_up_all(&vss->msg_empty);
>  	}
> diff --git a/sound/virtio/virtio_pcm_ops.c b/sound/virtio/virtio_pcm_ops.c
> index f8bfb87624be..4569b285f520 100644
> --- a/sound/virtio/virtio_pcm_ops.c
> +++ b/sound/virtio/virtio_pcm_ops.c
> @@ -282,7 +282,6 @@ static int virtsnd_pcm_prepare(struct snd_pcm_substream *substream)
>  
>  		vss->buffer_bytes = snd_pcm_lib_buffer_bytes(substream);
>  		vss->hw_ptr = 0;
> -		vss->msg_last_enqueued = -1;
>  	} else {
>  		struct snd_pcm_runtime *runtime = substream->runtime;
>  		unsigned int buffer_bytes = snd_pcm_lib_buffer_bytes(substream);
> @@ -324,7 +323,7 @@ static int virtsnd_pcm_trigger(struct snd_pcm_substream *substream, int command)
>  	struct virtio_snd_queue *queue;
>  	struct virtio_snd_msg *msg;
>  	unsigned long flags;
> -	int rc;
> +	int rc = 0;
>  
>  	switch (command) {
>  	case SNDRV_PCM_TRIGGER_START:
> @@ -333,7 +332,8 @@ static int virtsnd_pcm_trigger(struct snd_pcm_substream *substream, int command)
>  
>  		spin_lock_irqsave(&queue->lock, flags);
>  		spin_lock(&vss->lock);
> -		rc = virtsnd_pcm_msg_send(vss);
> +		if (vss->direction == SNDRV_PCM_STREAM_CAPTURE)
> +			rc = virtsnd_pcm_msg_send(vss, 0, vss->buffer_bytes);
>  		if (!rc)
>  			vss->xfer_enabled = true;
>  		spin_unlock(&vss->lock);
> @@ -450,15 +450,70 @@ virtsnd_pcm_pointer(struct snd_pcm_substream *substream)
>  	return hw_ptr;
>  }
>  
> +static int virtsnd_pcm_pb_silence(struct snd_pcm_substream *substream,
> +				  int channel, unsigned long pos,
> +				  unsigned long bytes)
> +{
> +	struct virtio_pcm_substream *vss = snd_pcm_substream_chip(substream);
> +	struct snd_pcm_runtime *runtime = substream->runtime;
> +
> +	snd_pcm_format_set_silence(runtime->format, runtime->dma_area + pos,
> +				   bytes_to_samples(runtime, bytes));
> +
> +	return virtsnd_pcm_msg_send_locked(vss, pos, bytes);
> +}
> +
> +static int virtsnd_pcm_pb_copy(struct snd_pcm_substream *substream, int channel,
> +			       unsigned long pos, struct iov_iter *iter,
> +			       unsigned long bytes)
> +{
> +	struct virtio_pcm_substream *vss = snd_pcm_substream_chip(substream);
> +	struct snd_pcm_runtime *runtime = substream->runtime;
> +
> +	if (copy_from_iter(runtime->dma_area + pos, bytes, iter) != bytes)
> +		return -EFAULT;
> +
> +	return virtsnd_pcm_msg_send_locked(vss, pos, bytes);
> +}
> +
> +static int virtsnd_pcm_cp_copy(struct snd_pcm_substream *substream, int channel,
> +			       unsigned long pos, struct iov_iter *iter,
> +			       unsigned long bytes)
> +{
> +	struct virtio_pcm_substream *vss = snd_pcm_substream_chip(substream);
> +	struct snd_pcm_runtime *runtime = substream->runtime;
> +
> +	if (copy_to_iter(runtime->dma_area + pos, bytes, iter) != bytes)
> +		return -EFAULT;
> +
> +	return virtsnd_pcm_msg_send_locked(vss, pos, bytes);
> +}
> +
>  /* 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,
> -	.sync_stop = virtsnd_pcm_sync_stop,
> -	.pointer = virtsnd_pcm_pointer,
> +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,
> +		.sync_stop = virtsnd_pcm_sync_stop,
> +		.pointer = virtsnd_pcm_pointer,
> +		.copy = virtsnd_pcm_pb_copy,
> +		.fill_silence = virtsnd_pcm_pb_silence,
> +	},
> +	{
> +		.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,
> +		.sync_stop = virtsnd_pcm_sync_stop,
> +		.pointer = virtsnd_pcm_pointer,
> +		.copy = virtsnd_pcm_cp_copy,
> +	},
>  };
> -- 
> 2.42.0
> 

Re: [RFC PATCH] ALSA: virtio: use copy and fill_silence callbacks

[Anton Yakovlev]

Hi Matias,

On 17.10.2023 21:54, Matias Ezequiel Vara Larsen wrote:
> Hello Anton,
> 
> Thanks for your help! I am going to send a second version of the patch
> with your changes. Is it OK if I add you with the "Co-developed-by"
> tag?.

Yes, I'm fine with that. :)


Best regards,

-- 
Anton Yakovlev
Senior Software Engineer

OpenSynergy GmbH
Rotherstr. 20, 10245 Berlin