sound/virtio/virtio_pcm_msg.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0+
 /*
  * virtio-snd: Virtio sound device
  * Copyright (C) 2021 OpenSynergy GmbH
  */
 #include <sound/pcm_params.h>

 #include "virtio_card.h"

 /**
  * struct virtio_pcm_msg - VirtIO I/O message.
  * @substream: VirtIO PCM substream.
  * @xfer: Request header payload.
  * @status: Response header payload.
  * @length: Data length in bytes.
  * @sgs: Payload scatter-gather table.
  */
 struct virtio_pcm_msg {
 	struct virtio_pcm_substream *substream;
 	struct virtio_snd_pcm_xfer xfer;
 	struct virtio_snd_pcm_status status;
 	size_t length;
 	struct scatterlist sgs[];
 };

 /**
  * enum pcm_msg_sg_index - Index values for the virtio_pcm_msg->sgs field in
  *                         an I/O message.
  * @PCM_MSG_SG_XFER: Element containing a virtio_snd_pcm_xfer structure.
  * @PCM_MSG_SG_STATUS: Element containing a virtio_snd_pcm_status structure.
  * @PCM_MSG_SG_DATA: The first element containing a data buffer.
  */
 enum pcm_msg_sg_index {
 	PCM_MSG_SG_XFER = 0,
 	PCM_MSG_SG_STATUS,
 	PCM_MSG_SG_DATA
 };

 /**
  * virtsnd_pcm_sg_num() - Count the number of sg-elements required to represent
  *                        vmalloc'ed buffer.
  * @data: Pointer to vmalloc'ed buffer.
  * @length: Buffer size.
  *
  * Context: Any context.
  * Return: Number of physically contiguous parts in the @data.
  */
 static int virtsnd_pcm_sg_num(u8 *data, unsigned int length)
 {
 	phys_addr_t sg_address;
 	unsigned int sg_length;
 	int num = 0;

 	while (length) {
 		struct page *pg = vmalloc_to_page(data);
 		phys_addr_t pg_address = page_to_phys(pg);
 		size_t pg_length;

 		pg_length = PAGE_SIZE - offset_in_page(data);
 		if (pg_length > length)
 			pg_length = length;

 		if (!num || sg_address + sg_length != pg_address) {
 			sg_address = pg_address;
 			sg_length = pg_length;
 			num++;
 		} else {
 			sg_length += pg_length;
 		}

 		data += pg_length;
 		length -= pg_length;
 	}

 	return num;
 }

 /**
  * virtsnd_pcm_sg_from() - Build sg-list from vmalloc'ed buffer.
  * @sgs: Preallocated sg-list to populate.
  * @nsgs: The maximum number of elements in the @sgs.
  * @data: Pointer to vmalloc'ed buffer.
  * @length: Buffer size.
  *
  * Splits the buffer into physically contiguous parts and makes an sg-list of
  * such parts.
  *
  * Context: Any context.
  */
 static void virtsnd_pcm_sg_from(struct scatterlist *sgs, int nsgs, u8 *data,
 				unsigned int length)
 {
 	int idx = -1;

 	while (length) {
 		struct page *pg = vmalloc_to_page(data);
 		size_t pg_length;

 		pg_length = PAGE_SIZE - offset_in_page(data);
 		if (pg_length > length)
 			pg_length = length;

 		if (idx == -1 ||
 		    sg_phys(&sgs[idx]) + sgs[idx].length != page_to_phys(pg)) {
 			if (idx + 1 == nsgs)
 				break;
 			sg_set_page(&sgs[++idx], pg, pg_length,
 				    offset_in_page(data));
 		} else {
 			sgs[idx].length += pg_length;
 		}

 		data += pg_length;
 		length -= pg_length;
 	}

 	sg_mark_end(&sgs[idx]);
 }

 /**
  * virtsnd_pcm_msg_alloc() - Allocate I/O messages.
  * @vss: VirtIO PCM substream.
  * @periods: Current number of periods.
  * @period_bytes: Current period size in bytes.
  *
  * The function slices the buffer into @periods parts (each with the size of
  * @period_bytes), and creates @periods corresponding I/O messages.
  *
  * Context: Any context that permits to sleep.
  * Return: 0 on success, -ENOMEM on failure.
  */
 int virtsnd_pcm_msg_alloc(struct virtio_pcm_substream *vss,
 			  unsigned int periods, unsigned int period_bytes)
 {
 	struct snd_pcm_runtime *runtime = vss->substream->runtime;
 	unsigned int i;

 	vss->msgs = kcalloc(periods, sizeof(*vss->msgs), GFP_KERNEL);
 	if (!vss->msgs)
 		return -ENOMEM;

 	vss->nmsgs = periods;

 	for (i = 0; i < periods; ++i) {
 		u8 *data = runtime->dma_area + period_bytes * i;
 		int sg_num = virtsnd_pcm_sg_num(data, period_bytes);
 		struct virtio_pcm_msg *msg;

 		msg = kzalloc(struct_size(msg, sgs, sg_num + 2), GFP_KERNEL);
 		if (!msg)
 			return -ENOMEM;

 		msg->substream = vss;
 		sg_init_one(&msg->sgs[PCM_MSG_SG_XFER], &msg->xfer,
 			    sizeof(msg->xfer));
 		sg_init_one(&msg->sgs[PCM_MSG_SG_STATUS], &msg->status,
 			    sizeof(msg->status));
 		virtsnd_pcm_sg_from(&msg->sgs[PCM_MSG_SG_DATA], sg_num, data,
 				    period_bytes);

 		vss->msgs[i] = msg;
 	}

 	return 0;
 }

 /**
  * virtsnd_pcm_msg_free() - Free all allocated I/O messages.
  * @vss: VirtIO PCM substream.
  *
  * Context: Any context.
  */
 void virtsnd_pcm_msg_free(struct virtio_pcm_substream *vss)
 {
 	unsigned int i;

 	for (i = 0; vss->msgs && i < vss->nmsgs; ++i)
 		kfree(vss->msgs[i]);
 	kfree(vss->msgs);

 	vss->msgs = NULL;
 	vss->nmsgs = 0;
 }

 /**
  * virtsnd_pcm_msg_send() - Send asynchronous I/O messages.
  * @vss: VirtIO PCM substream.
  * @offset: starting position that has been updated
  * @bytes: number of bytes that has been updated
  *
  * 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 uses offset and bytes to calculate the
  * messages that need to be added.
  *
  * Context: Any context. Expects the tx/rx queue and the VirtIO substream
  *          spinlocks to be held by caller.
  * Return: 0 on success, -errno on failure.
  */
 int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss, unsigned long offset,
 			 unsigned long bytes)
 {
 	struct virtio_snd *snd = vss->snd;
 	struct virtio_device *vdev = snd->vdev;
 	struct virtqueue *vqueue = virtsnd_pcm_queue(vss)->vqueue;
 	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;

 	start = offset / period_bytes;
 	end = (offset + bytes - 1) / period_bytes;

 	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]
 		};
 		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++;
 		}

 		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);

 	if (notify)
 		virtqueue_notify(vqueue);

 	return 0;
 }

 /**
  * virtsnd_pcm_msg_pending_num() - Returns the number of pending I/O messages.
  * @vss: VirtIO substream.
  *
  * Context: Any context.
  * Return: Number of messages.
  */
 unsigned int virtsnd_pcm_msg_pending_num(struct virtio_pcm_substream *vss)
 {
 	unsigned int num;
 	unsigned long flags;

 	spin_lock_irqsave(&vss->lock, flags);
 	num = vss->msg_count;
 	spin_unlock_irqrestore(&vss->lock, flags);

 	return num;
 }

 /**
  * virtsnd_pcm_msg_complete() - Complete an I/O message.
  * @msg: I/O message.
  * @written_bytes: Number of bytes written to the message.
  *
  * Completion of the message means the elapsed period. If transmission is
  * allowed, then each completed message is immediately placed back at the end
  * of the queue.
  *
  * For the playback substream, @written_bytes is equal to sizeof(msg->status).
  *
  * For the capture substream, @written_bytes is equal to sizeof(msg->status)
  * plus the number of captured bytes.
  *
  * Context: Interrupt context. Takes and releases the VirtIO substream spinlock.
  */
 static void virtsnd_pcm_msg_complete(struct virtio_pcm_msg *msg,
 				     size_t written_bytes)
 {
 	struct virtio_pcm_substream *vss = msg->substream;

 	/*
 	 * hw_ptr always indicates the buffer position of the first I/O message
 	 * in the virtqueue. Therefore, on each completion of an I/O message,
 	 * the hw_ptr value is unconditionally advanced.
 	 */
 	spin_lock(&vss->lock);
 	/*
 	 * If the capture substream returned an incorrect status, then just
 	 * increase the hw_ptr by the message size.
 	 */
 	if (vss->direction == SNDRV_PCM_STREAM_PLAYBACK ||
 	    written_bytes <= sizeof(msg->status))
 		vss->hw_ptr += msg->length;
 	else
 		vss->hw_ptr += written_bytes - sizeof(msg->status);

 	if (vss->hw_ptr >= vss->buffer_bytes)
 		vss->hw_ptr -= vss->buffer_bytes;

 	msg->length = 0;

 	vss->xfer_xrun = false;
 	vss->msg_count--;

 	if (vss->xfer_enabled) {
 		struct snd_pcm_runtime *runtime = vss->substream->runtime;

 		runtime->delay =
 			bytes_to_frames(runtime,
 					le32_to_cpu(msg->status.latency_bytes));

 		schedule_work(&vss->elapsed_period);
 	} else if (!vss->msg_count) {
 		wake_up_all(&vss->msg_empty);
 	}
 	spin_unlock(&vss->lock);
 }

 /**
  * virtsnd_pcm_notify_cb() - Process all completed I/O messages.
  * @queue: Underlying tx/rx virtqueue.
  *
  * Context: Interrupt context. Takes and releases the tx/rx queue spinlock.
  */
 static inline void virtsnd_pcm_notify_cb(struct virtio_snd_queue *queue)
 {
 	struct virtio_pcm_msg *msg;
 	u32 written_bytes;
 	unsigned long flags;

 	spin_lock_irqsave(&queue->lock, flags);
 	do {
 		virtqueue_disable_cb(queue->vqueue);
 		while ((msg = virtqueue_get_buf(queue->vqueue, &written_bytes)))
 			virtsnd_pcm_msg_complete(msg, written_bytes);
 	} while (!virtqueue_enable_cb(queue->vqueue));
 	spin_unlock_irqrestore(&queue->lock, flags);
 }

 /**
  * virtsnd_pcm_tx_notify_cb() - Process all completed TX messages.
  * @vqueue: Underlying tx virtqueue.
  *
  * Context: Interrupt context.
  */
 void virtsnd_pcm_tx_notify_cb(struct virtqueue *vqueue)
 {
 	struct virtio_snd *snd = vqueue->vdev->priv;

 	virtsnd_pcm_notify_cb(virtsnd_tx_queue(snd));
 }

 /**
  * virtsnd_pcm_rx_notify_cb() - Process all completed RX messages.
  * @vqueue: Underlying rx virtqueue.
  *
  * Context: Interrupt context.
  */
 void virtsnd_pcm_rx_notify_cb(struct virtqueue *vqueue)
 {
 	struct virtio_snd *snd = vqueue->vdev->priv;

 	virtsnd_pcm_notify_cb(virtsnd_rx_queue(snd));
 }

 /**
  * virtsnd_pcm_ctl_msg_alloc() - Allocate and initialize the PCM device control
  *                               message for the specified substream.
  * @vss: VirtIO PCM substream.
  * @command: Control request code (VIRTIO_SND_R_PCM_XXX).
  * @gfp: Kernel flags for memory allocation.
  *
  * Context: Any context. May sleep if @gfp flags permit.
  * Return: Allocated message on success, NULL on failure.
  */
 struct virtio_snd_msg *
 virtsnd_pcm_ctl_msg_alloc(struct virtio_pcm_substream *vss,
 			  unsigned int command, gfp_t gfp)
 {
 	size_t request_size = sizeof(struct virtio_snd_pcm_hdr);
 	size_t response_size = sizeof(struct virtio_snd_hdr);
 	struct virtio_snd_msg *msg;

 	switch (command) {
 	case VIRTIO_SND_R_PCM_SET_PARAMS:
 		request_size = sizeof(struct virtio_snd_pcm_set_params);
 		break;
 	}

 	msg = virtsnd_ctl_msg_alloc(request_size, response_size, gfp);
 	if (msg) {
 		struct virtio_snd_pcm_hdr *hdr = virtsnd_ctl_msg_request(msg);

 		hdr->hdr.code = cpu_to_le32(command);
 		hdr->stream_id = cpu_to_le32(vss->sid);
 	}

 	return msg;
 }
	// SPDX-License-Identifier: GPL-2.0+
	/*
	* virtio-snd: Virtio sound device
	* Copyright (C) 2021 OpenSynergy GmbH
	*/
	#include <sound/pcm_params.h>

	#include "virtio_card.h"

	/**
	* struct virtio_pcm_msg - VirtIO I/O message.
	* @substream: VirtIO PCM substream.
	* @xfer: Request header payload.
	* @status: Response header payload.
	* @length: Data length in bytes.
	* @sgs: Payload scatter-gather table.
	*/
	struct virtio_pcm_msg {
	struct virtio_pcm_substream *substream;
	struct virtio_snd_pcm_xfer xfer;
	struct virtio_snd_pcm_status status;
	size_t length;
	struct scatterlist sgs[];
	};

	/**
	* enum pcm_msg_sg_index - Index values for the virtio_pcm_msg->sgs field in
	* an I/O message.
	* @PCM_MSG_SG_XFER: Element containing a virtio_snd_pcm_xfer structure.
	* @PCM_MSG_SG_STATUS: Element containing a virtio_snd_pcm_status structure.
	* @PCM_MSG_SG_DATA: The first element containing a data buffer.
	*/
	enum pcm_msg_sg_index {
	PCM_MSG_SG_XFER = 0,
	PCM_MSG_SG_STATUS,
	PCM_MSG_SG_DATA
	};

	/**
	* virtsnd_pcm_sg_num() - Count the number of sg-elements required to represent
	* vmalloc'ed buffer.
	* @data: Pointer to vmalloc'ed buffer.
	* @length: Buffer size.
	*
	* Context: Any context.
	* Return: Number of physically contiguous parts in the @data.
	*/
	static int virtsnd_pcm_sg_num(u8 *data, unsigned int length)
	{
	phys_addr_t sg_address;
	unsigned int sg_length;
	int num = 0;

	while (length) {
	struct page *pg = vmalloc_to_page(data);
	phys_addr_t pg_address = page_to_phys(pg);
	size_t pg_length;

	pg_length = PAGE_SIZE - offset_in_page(data);
	if (pg_length > length)
	pg_length = length;

	if (!num \|\| sg_address + sg_length != pg_address) {
	sg_address = pg_address;
	sg_length = pg_length;
	num++;
	} else {
	sg_length += pg_length;
	}

	data += pg_length;
	length -= pg_length;
	}

	return num;
	}

	/**
	* virtsnd_pcm_sg_from() - Build sg-list from vmalloc'ed buffer.
	* @sgs: Preallocated sg-list to populate.
	* @nsgs: The maximum number of elements in the @sgs.
	* @data: Pointer to vmalloc'ed buffer.
	* @length: Buffer size.
	*
	* Splits the buffer into physically contiguous parts and makes an sg-list of
	* such parts.
	*
	* Context: Any context.
	*/
	static void virtsnd_pcm_sg_from(struct scatterlist sgs, int nsgs, u8 data,
	unsigned int length)
	{
	int idx = -1;

	while (length) {
	struct page *pg = vmalloc_to_page(data);
	size_t pg_length;

	pg_length = PAGE_SIZE - offset_in_page(data);
	if (pg_length > length)
	pg_length = length;

	if (idx == -1 \|\|
	sg_phys(&sgs[idx]) + sgs[idx].length != page_to_phys(pg)) {
	if (idx + 1 == nsgs)
	break;
	sg_set_page(&sgs[++idx], pg, pg_length,
	offset_in_page(data));
	} else {
	sgs[idx].length += pg_length;
	}

	data += pg_length;
	length -= pg_length;
	}

	sg_mark_end(&sgs[idx]);
	}

	/**
	* virtsnd_pcm_msg_alloc() - Allocate I/O messages.
	* @vss: VirtIO PCM substream.
	* @periods: Current number of periods.
	* @period_bytes: Current period size in bytes.
	*
	* The function slices the buffer into @periods parts (each with the size of
	* @period_bytes), and creates @periods corresponding I/O messages.
	*
	* Context: Any context that permits to sleep.
	* Return: 0 on success, -ENOMEM on failure.
	*/
	int virtsnd_pcm_msg_alloc(struct virtio_pcm_substream *vss,
	unsigned int periods, unsigned int period_bytes)
	{
	struct snd_pcm_runtime *runtime = vss->substream->runtime;
	unsigned int i;

	vss->msgs = kcalloc(periods, sizeof(*vss->msgs), GFP_KERNEL);
	if (!vss->msgs)
	return -ENOMEM;

	vss->nmsgs = periods;

	for (i = 0; i < periods; ++i) {
	u8 data = runtime->dma_area + period_bytes i;
	int sg_num = virtsnd_pcm_sg_num(data, period_bytes);
	struct virtio_pcm_msg *msg;

	msg = kzalloc(struct_size(msg, sgs, sg_num + 2), GFP_KERNEL);
	if (!msg)
	return -ENOMEM;

	msg->substream = vss;
	sg_init_one(&msg->sgs[PCM_MSG_SG_XFER], &msg->xfer,
	sizeof(msg->xfer));
	sg_init_one(&msg->sgs[PCM_MSG_SG_STATUS], &msg->status,
	sizeof(msg->status));
	virtsnd_pcm_sg_from(&msg->sgs[PCM_MSG_SG_DATA], sg_num, data,
	period_bytes);

	vss->msgs[i] = msg;
	}

	return 0;
	}

	/**
	* virtsnd_pcm_msg_free() - Free all allocated I/O messages.
	* @vss: VirtIO PCM substream.
	*
	* Context: Any context.
	*/
	void virtsnd_pcm_msg_free(struct virtio_pcm_substream *vss)
	{
	unsigned int i;

	for (i = 0; vss->msgs && i < vss->nmsgs; ++i)
	kfree(vss->msgs[i]);
	kfree(vss->msgs);

	vss->msgs = NULL;
	vss->nmsgs = 0;
	}

	/**
	* virtsnd_pcm_msg_send() - Send asynchronous I/O messages.
	* @vss: VirtIO PCM substream.
	* @offset: starting position that has been updated
	* @bytes: number of bytes that has been updated
	*
	* 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 uses offset and bytes to calculate the
	* messages that need to be added.
	*
	* Context: Any context. Expects the tx/rx queue and the VirtIO substream
	* spinlocks to be held by caller.
	* Return: 0 on success, -errno on failure.
	*/
	int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss, unsigned long offset,
	unsigned long bytes)
	{
	struct virtio_snd *snd = vss->snd;
	struct virtio_device *vdev = snd->vdev;
	struct virtqueue *vqueue = virtsnd_pcm_queue(vss)->vqueue;
	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;

	start = offset / period_bytes;
	end = (offset + bytes - 1) / period_bytes;

	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]
	};
	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++;
	}

	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);

	if (notify)
	virtqueue_notify(vqueue);

	return 0;
	}

	/**
	* virtsnd_pcm_msg_pending_num() - Returns the number of pending I/O messages.
	* @vss: VirtIO substream.
	*
	* Context: Any context.
	* Return: Number of messages.
	*/
	unsigned int virtsnd_pcm_msg_pending_num(struct virtio_pcm_substream *vss)
	{
	unsigned int num;
	unsigned long flags;

	spin_lock_irqsave(&vss->lock, flags);
	num = vss->msg_count;
	spin_unlock_irqrestore(&vss->lock, flags);

	return num;
	}

	/**
	* virtsnd_pcm_msg_complete() - Complete an I/O message.
	* @msg: I/O message.
	* @written_bytes: Number of bytes written to the message.
	*
	* Completion of the message means the elapsed period. If transmission is
	* allowed, then each completed message is immediately placed back at the end
	* of the queue.
	*
	* For the playback substream, @written_bytes is equal to sizeof(msg->status).
	*
	* For the capture substream, @written_bytes is equal to sizeof(msg->status)
	* plus the number of captured bytes.
	*
	* Context: Interrupt context. Takes and releases the VirtIO substream spinlock.
	*/
	static void virtsnd_pcm_msg_complete(struct virtio_pcm_msg *msg,
	size_t written_bytes)
	{
	struct virtio_pcm_substream *vss = msg->substream;

	/*
	* hw_ptr always indicates the buffer position of the first I/O message
	* in the virtqueue. Therefore, on each completion of an I/O message,
	* the hw_ptr value is unconditionally advanced.
	*/
	spin_lock(&vss->lock);
	/*
	* If the capture substream returned an incorrect status, then just
	* increase the hw_ptr by the message size.
	*/
	if (vss->direction == SNDRV_PCM_STREAM_PLAYBACK \|\|
	written_bytes <= sizeof(msg->status))
	vss->hw_ptr += msg->length;
	else
	vss->hw_ptr += written_bytes - sizeof(msg->status);

	if (vss->hw_ptr >= vss->buffer_bytes)
	vss->hw_ptr -= vss->buffer_bytes;

	msg->length = 0;

	vss->xfer_xrun = false;
	vss->msg_count--;

	if (vss->xfer_enabled) {
	struct snd_pcm_runtime *runtime = vss->substream->runtime;

	runtime->delay =
	bytes_to_frames(runtime,
	le32_to_cpu(msg->status.latency_bytes));

	schedule_work(&vss->elapsed_period);
	} else if (!vss->msg_count) {
	wake_up_all(&vss->msg_empty);
	}
	spin_unlock(&vss->lock);
	}

	/**
	* virtsnd_pcm_notify_cb() - Process all completed I/O messages.
	* @queue: Underlying tx/rx virtqueue.
	*
	* Context: Interrupt context. Takes and releases the tx/rx queue spinlock.
	*/
	static inline void virtsnd_pcm_notify_cb(struct virtio_snd_queue *queue)
	{
	struct virtio_pcm_msg *msg;
	u32 written_bytes;
	unsigned long flags;

	spin_lock_irqsave(&queue->lock, flags);
	do {
	virtqueue_disable_cb(queue->vqueue);
	while ((msg = virtqueue_get_buf(queue->vqueue, &written_bytes)))
	virtsnd_pcm_msg_complete(msg, written_bytes);
	} while (!virtqueue_enable_cb(queue->vqueue));
	spin_unlock_irqrestore(&queue->lock, flags);
	}

	/**
	* virtsnd_pcm_tx_notify_cb() - Process all completed TX messages.
	* @vqueue: Underlying tx virtqueue.
	*
	* Context: Interrupt context.
	*/
	void virtsnd_pcm_tx_notify_cb(struct virtqueue *vqueue)
	{
	struct virtio_snd *snd = vqueue->vdev->priv;

	virtsnd_pcm_notify_cb(virtsnd_tx_queue(snd));
	}

	/**
	* virtsnd_pcm_rx_notify_cb() - Process all completed RX messages.
	* @vqueue: Underlying rx virtqueue.
	*
	* Context: Interrupt context.
	*/
	void virtsnd_pcm_rx_notify_cb(struct virtqueue *vqueue)
	{
	struct virtio_snd *snd = vqueue->vdev->priv;

	virtsnd_pcm_notify_cb(virtsnd_rx_queue(snd));
	}

	/**
	* virtsnd_pcm_ctl_msg_alloc() - Allocate and initialize the PCM device control
	* message for the specified substream.
	* @vss: VirtIO PCM substream.
	* @command: Control request code (VIRTIO_SND_R_PCM_XXX).
	* @gfp: Kernel flags for memory allocation.
	*
	* Context: Any context. May sleep if @gfp flags permit.
	* Return: Allocated message on success, NULL on failure.
	*/
	struct virtio_snd_msg *
	virtsnd_pcm_ctl_msg_alloc(struct virtio_pcm_substream *vss,
	unsigned int command, gfp_t gfp)
	{
	size_t request_size = sizeof(struct virtio_snd_pcm_hdr);
	size_t response_size = sizeof(struct virtio_snd_hdr);
	struct virtio_snd_msg *msg;

	switch (command) {
	case VIRTIO_SND_R_PCM_SET_PARAMS:
	request_size = sizeof(struct virtio_snd_pcm_set_params);
	break;
	}

	msg = virtsnd_ctl_msg_alloc(request_size, response_size, gfp);
	if (msg) {
	struct virtio_snd_pcm_hdr *hdr = virtsnd_ctl_msg_request(msg);

	hdr->hdr.code = cpu_to_le32(command);
	hdr->stream_id = cpu_to_le32(vss->sid);
	}

	return msg;
	}