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Subject: Re: [PATCH 4/7] ALSA: virtio: handling control and I/O messages for
 the PCM device
To:     "Michael S. Tsirkin" <mst@redhat.com>
CC:     <virtualization@lists.linux-foundation.org>,
        <alsa-devel@alsa-project.org>, <virtio-dev@lists.oasis-open.org>,
        <linux-kernel@vger.kernel.org>, Takashi Iwai <tiwai@suse.com>
References: <20210120003638.3339987-1-anton.yakovlev@opensynergy.com>
 <20210120003638.3339987-5-anton.yakovlev@opensynergy.com>
 <20210120032711-mutt-send-email-mst@kernel.org>
From:   Anton Yakovlev <anton.yakovlev@opensynergy.com>
Message-ID: <59121ced-c306-ee7b-b98d-8fa2674326ad@opensynergy.com>
Date:   Sun, 24 Jan 2021 17:49:52 +0100
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On 20.01.2021 09:29, Michael S. Tsirkin wrote:
> CAUTION: This email originated from outside of the organization.
> Do not click links or open attachments unless you recognize the sender and know the content is safe.
> 
> 
> On Wed, Jan 20, 2021 at 01:36:32AM +0100, Anton Yakovlev wrote:
>> The driver implements a message-based transport for I/O substream
>> operations. Before the start of the substream, the hardware buffer is
>> sliced into I/O messages, the number of which is equal to the current
>> number of periods. The size of each message is equal to the current
>> size of one period.
>>
>> I/O messages are organized in an ordered queue. The completion of the
>> I/O message indicates an expired period (the only exception is the end
>> of the stream for the capture substream). Upon completion, the message
>> is automatically re-added to the end of the queue.
>>
>> When an I/O message is completed, the hw_ptr value is incremented
>> unconditionally (to ensure that the hw_ptr always correctly reflects
>> the state of the messages in the virtqueue). Due to its asynchronous
>> nature, a message can be completed when the runtime structure no longer
>> exists. For this reason, the values from this structure are cached in
>> the virtio substream, which are required to calculate the new value of
>> the hw_ptr.
>>
>> Signed-off-by: Anton Yakovlev <anton.yakovlev@opensynergy.com>
>> ---
>>   sound/virtio/Makefile         |   3 +-
>>   sound/virtio/virtio_card.c    |  33 ++++
>>   sound/virtio/virtio_card.h    |   9 +
>>   sound/virtio/virtio_pcm.c     |   3 +
>>   sound/virtio/virtio_pcm.h     |  31 ++++
>>   sound/virtio/virtio_pcm_msg.c | 317 ++++++++++++++++++++++++++++++++++
>>   6 files changed, 395 insertions(+), 1 deletion(-)
>>   create mode 100644 sound/virtio/virtio_pcm_msg.c
>>
>> diff --git a/sound/virtio/Makefile b/sound/virtio/Makefile
>> index 69162a545a41..626af3cc3ed7 100644
>> --- a/sound/virtio/Makefile
>> +++ b/sound/virtio/Makefile
>> @@ -5,5 +5,6 @@ obj-$(CONFIG_SND_VIRTIO) += virtio_snd.o
>>   virtio_snd-objs := \
>>        virtio_card.o \
>>        virtio_ctl_msg.o \
>> -     virtio_pcm.o
>> +     virtio_pcm.o \
>> +     virtio_pcm_msg.o
>>
>> diff --git a/sound/virtio/virtio_card.c b/sound/virtio/virtio_card.c
>> index 293d497f24e7..dc703fc662f5 100644
>> --- a/sound/virtio/virtio_card.c
>> +++ b/sound/virtio/virtio_card.c
>> @@ -145,6 +145,12 @@ static int virtsnd_find_vqs(struct virtio_snd *snd)
>>        callbacks[VIRTIO_SND_VQ_CONTROL] = virtsnd_ctl_notify_cb;
>>        callbacks[VIRTIO_SND_VQ_EVENT] = virtsnd_event_notify_cb;
>>
>> +     virtio_cread(vdev, struct virtio_snd_config, streams, &n);
>> +     if (n) {
>> +             callbacks[VIRTIO_SND_VQ_TX] = virtsnd_pcm_tx_notify_cb;
>> +             callbacks[VIRTIO_SND_VQ_RX] = virtsnd_pcm_rx_notify_cb;
>> +     }
>> +
>>        rc = virtio_find_vqs(vdev, VIRTIO_SND_VQ_MAX, vqs, callbacks, names,
>>                             NULL);
>>        if (rc) {
>> @@ -186,15 +192,42 @@ static int virtsnd_find_vqs(struct virtio_snd *snd)
>>    * virtsnd_enable_vqs() - Enable the event, tx and rx virtqueues.
>>    * @snd: VirtIO sound device.
>>    *
>> + * The tx queue is enabled only if the device supports playback stream(s).
>> + *
>> + * The rx queue is enabled only if the device supports capture stream(s).
>> + *
>>    * Context: Any context.
>>    */
>>   static void virtsnd_enable_vqs(struct virtio_snd *snd)
>>   {
>> +     struct virtio_device *vdev = snd->vdev;
>>        struct virtqueue *vqueue;
>> +     struct virtio_pcm *pcm;
>> +     unsigned int npbs = 0;
>> +     unsigned int ncps = 0;
>>
>>        vqueue = snd->queues[VIRTIO_SND_VQ_EVENT].vqueue;
>>        if (!virtqueue_enable_cb(vqueue))
>>                virtsnd_event_notify_cb(vqueue);
>> +
>> +     list_for_each_entry(pcm, &snd->pcm_list, list) {
>> +             npbs += pcm->streams[SNDRV_PCM_STREAM_PLAYBACK].nsubstreams;
>> +             ncps += pcm->streams[SNDRV_PCM_STREAM_CAPTURE].nsubstreams;
>> +     }
>> +
>> +     if (npbs) {
>> +             vqueue = snd->queues[VIRTIO_SND_VQ_TX].vqueue;
>> +             if (!virtqueue_enable_cb(vqueue))
>> +                     dev_warn(&vdev->dev,
>> +                              "suspicious notification in the TX queue\n");
>> +     }
>> +
>> +     if (ncps) {
>> +             vqueue = snd->queues[VIRTIO_SND_VQ_RX].vqueue;
>> +             if (!virtqueue_enable_cb(vqueue))
>> +                     dev_warn(&vdev->dev,
>> +                              "suspicious notification in the RX queue\n");
>> +     }
> 
> Not sure how all this prevents use of same vq from multiple threads ...
> And why are we sure there are no buffers yet?  If that is because
> nothing yet happened, then I'd also like to point out that a vq starts
> out with callbacks enabled, so you don't need to do that first thing ...

Yes, I redone that logic in v2.


>>   }
>>
>>   /**
>> diff --git a/sound/virtio/virtio_card.h b/sound/virtio/virtio_card.h
>> index be6651a6aaf8..b11c09984882 100644
>> --- a/sound/virtio/virtio_card.h
>> +++ b/sound/virtio/virtio_card.h
>> @@ -89,4 +89,13 @@ virtsnd_rx_queue(struct virtio_snd *snd)
>>        return &snd->queues[VIRTIO_SND_VQ_RX];
>>   }
>>
>> +static inline struct virtio_snd_queue *
>> +virtsnd_pcm_queue(struct virtio_pcm_substream *substream)
>> +{
>> +     if (substream->direction == SNDRV_PCM_STREAM_PLAYBACK)
>> +             return virtsnd_tx_queue(substream->snd);
>> +     else
>> +             return virtsnd_rx_queue(substream->snd);
>> +}
>> +
>>   #endif /* VIRTIO_SND_CARD_H */
>> diff --git a/sound/virtio/virtio_pcm.c b/sound/virtio/virtio_pcm.c
>> index 036990b7b78a..1ab50dcc88c8 100644
>> --- a/sound/virtio/virtio_pcm.c
>> +++ b/sound/virtio/virtio_pcm.c
>> @@ -376,6 +376,7 @@ int virtsnd_pcm_parse_cfg(struct virtio_snd *snd)
>>
>>                substream->snd = snd;
>>                substream->sid = i;
>> +             init_waitqueue_head(&substream->msg_empty);
>>
>>                rc = virtsnd_pcm_build_hw(substream, &info[i]);
>>                if (rc)
>> @@ -530,6 +531,8 @@ void virtsnd_pcm_event(struct virtio_snd *snd, struct virtio_snd_event *event)
>>                break;
>>        }
>>        case VIRTIO_SND_EVT_PCM_XRUN: {
>> +             if (atomic_read(&substream->xfer_enabled))
>> +                     atomic_set(&substream->xfer_xrun, 1);
>>                break;
>>        }
>>        }
>> diff --git a/sound/virtio/virtio_pcm.h b/sound/virtio/virtio_pcm.h
>> index 73fb4d9dc524..d011b7e1d18d 100644
>> --- a/sound/virtio/virtio_pcm.h
>> +++ b/sound/virtio/virtio_pcm.h
>> @@ -24,6 +24,7 @@
>>   #include <sound/pcm.h>
>>
>>   struct virtio_pcm;
>> +struct virtio_pcm_msg;
>>
>>   /**
>>    * struct virtio_pcm_substream - VirtIO PCM substream.
>> @@ -34,6 +35,16 @@ struct virtio_pcm;
>>    * @features: Stream VirtIO feature bit map (1 << VIRTIO_SND_PCM_F_XXX).
>>    * @substream: Kernel ALSA substream.
>>    * @hw: Kernel ALSA substream hardware descriptor.
>> + * @frame_bytes: Current frame size in bytes.
>> + * @period_size: Current period size in frames.
>> + * @buffer_size: Current buffer size in frames.
>> + * @hw_ptr: Substream hardware pointer value in frames [0 ... buffer_size).
>> + * @xfer_enabled: Data transfer state (0 - off, 1 - on).
>> + * @xfer_xrun: Data underflow/overflow state (0 - no xrun, 1 - xrun).
>> + * @msgs: I/O messages.
>> + * @msg_last_enqueued: Index of the last I/O message added to the virtqueue.
>> + * @msg_count: Number of pending I/O messages in the virtqueue.
>> + * @msg_empty: Notify when msg_count is zero.
>>    */
>>   struct virtio_pcm_substream {
>>        struct virtio_snd *snd;
>> @@ -43,6 +54,16 @@ struct virtio_pcm_substream {
>>        u32 features;
>>        struct snd_pcm_substream *substream;
>>        struct snd_pcm_hardware hw;
>> +     unsigned int frame_bytes;
>> +     snd_pcm_uframes_t period_size;
>> +     snd_pcm_uframes_t buffer_size;
>> +     atomic_t hw_ptr;
>> +     atomic_t xfer_enabled;
>> +     atomic_t xfer_xrun;
>> +     struct virtio_pcm_msg *msgs;
>> +     int msg_last_enqueued;
>> +     atomic_t msg_count;
>> +     wait_queue_head_t msg_empty;
>>   };
>>
>>   /**
>> @@ -86,4 +107,14 @@ struct virtio_pcm *virtsnd_pcm_find(struct virtio_snd *snd, unsigned int nid);
>>   struct virtio_pcm *virtsnd_pcm_find_or_create(struct virtio_snd *snd,
>>                                              unsigned int nid);
>>
>> +struct virtio_snd_msg *
>> +virtsnd_pcm_ctl_msg_alloc(struct virtio_pcm_substream *substream,
>> +                       unsigned int command, gfp_t gfp);
>> +
>> +int virtsnd_pcm_msg_alloc(struct virtio_pcm_substream *substream,
>> +                       unsigned int nmsg, u8 *dma_area,
>> +                       unsigned int period_bytes);
>> +
>> +int virtsnd_pcm_msg_send(struct virtio_pcm_substream *substream);
>> +
>>   #endif /* VIRTIO_SND_PCM_H */
>> diff --git a/sound/virtio/virtio_pcm_msg.c b/sound/virtio/virtio_pcm_msg.c
>> new file mode 100644
>> index 000000000000..cfbe5935527a
>> --- /dev/null
>> +++ b/sound/virtio/virtio_pcm_msg.c
>> @@ -0,0 +1,317 @@
>> +// SPDX-License-Identifier: GPL-2.0+
>> +/*
>> + * Sound card driver for virtio
>> + * Copyright (C) 2020  OpenSynergy GmbH
>> + *
>> + * This program is free software; you can redistribute it and/or modify
>> + * it under the terms of the GNU General Public License as published by
>> + * the Free Software Foundation; either version 2 of the License, or
>> + * (at your option) any later version.
>> + *
>> + * This program is distributed in the hope that it will be useful,
>> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
>> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
>> + * GNU General Public License for more details.
>> + *
>> + * You should have received a copy of the GNU General Public License
>> + * along with this program; if not, see <http://www.gnu.org/licenses/>.
>> + */
>> +#include <sound/pcm_params.h>
>> +
>> +#include "virtio_card.h"
>> +
>> +/**
>> + * enum pcm_msg_sg_index - Scatter-gather element indexes for an I/O message.
>> + * @PCM_MSG_SG_XFER: Element containing a virtio_snd_pcm_xfer structure.
>> + * @PCM_MSG_SG_DATA: Element containing a data buffer.
>> + * @PCM_MSG_SG_STATUS: Element containing a virtio_snd_pcm_status structure.
>> + * @PCM_MSG_SG_MAX: The maximum number of elements in the scatter-gather table.
>> + *
>> + * These values are used as the index of the payload scatter-gather table.
>> + */
>> +enum pcm_msg_sg_index {
>> +     PCM_MSG_SG_XFER = 0,
>> +     PCM_MSG_SG_DATA,
>> +     PCM_MSG_SG_STATUS,
>> +     PCM_MSG_SG_MAX
>> +};
>> +
>> +/**
>> + * struct virtio_pcm_msg - VirtIO I/O message.
>> + * @substream: VirtIO PCM substream.
>> + * @xfer: Request header payload.
>> + * @status: Response header payload.
>> + * @sgs: Payload scatter-gather table.
>> + */
>> +struct virtio_pcm_msg {
>> +     struct virtio_pcm_substream *substream;
>> +     struct virtio_snd_pcm_xfer xfer;
>> +     struct virtio_snd_pcm_status status;
>> +     struct scatterlist sgs[PCM_MSG_SG_MAX];
>> +};
>> +
>> +/**
>> + * virtsnd_pcm_msg_alloc() - Allocate I/O messages.
>> + * @substream: VirtIO PCM substream.
>> + * @nmsg: Number of messages (equal to the number of periods).
>> + * @dma_area: Pointer to used audio buffer.
>> + * @period_bytes: Period (message payload) size.
>> + *
>> + * The function slices the buffer into nmsg parts (each with the size of
>> + * period_bytes), and creates nmsg 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 *substream,
>> +                       unsigned int nmsg, u8 *dma_area,
>> +                       unsigned int period_bytes)
>> +{
>> +     struct virtio_device *vdev = substream->snd->vdev;
>> +     unsigned int i;
>> +
>> +     if (substream->msgs)
>> +             devm_kfree(&vdev->dev, substream->msgs);
>> +
>> +     substream->msgs = devm_kcalloc(&vdev->dev, nmsg,
>> +                                    sizeof(*substream->msgs), GFP_KERNEL);
>> +     if (!substream->msgs)
>> +             return -ENOMEM;
>> +
>> +     for (i = 0; i < nmsg; ++i) {
>> +             struct virtio_pcm_msg *msg = &substream->msgs[i];
>> +
>> +             msg->substream = substream;
>> +
>> +             sg_init_table(msg->sgs, PCM_MSG_SG_MAX);
>> +             sg_init_one(&msg->sgs[PCM_MSG_SG_XFER], &msg->xfer,
>> +                         sizeof(msg->xfer));
>> +             sg_init_one(&msg->sgs[PCM_MSG_SG_DATA],
>> +                         dma_area + period_bytes * i, period_bytes);
>> +             sg_init_one(&msg->sgs[PCM_MSG_SG_STATUS], &msg->status,
>> +                         sizeof(msg->status));
>> +     }
>> +
>> +     return 0;
>> +}
>> +
>> +/**
>> + * virtsnd_pcm_msg_send() - Send asynchronous I/O messages.
>> + * @substream: VirtIO PCM substream.
>> + *
>> + * All messages are organized in an ordered circular list. Each time the
>> + * function is called, all currently non-enqueued messages are added to the
>> + * virtqueue. For this, the function keeps track of two values:
>> + *
>> + *   msg_last_enqueued = index of the last enqueued message,
>> + *   msg_count = # of pending messages in the virtqueue.
>> + *
>> + * Context: Any context.
>> + * Return: 0 on success, -EIO on failure.
>> + */
>> +int virtsnd_pcm_msg_send(struct virtio_pcm_substream *substream)
>> +{
>> +     struct snd_pcm_runtime *runtime = substream->substream->runtime;
>> +     struct virtio_snd *snd = substream->snd;
>> +     struct virtio_device *vdev = snd->vdev;
>> +     struct virtqueue *vqueue = virtsnd_pcm_queue(substream)->vqueue;
>> +     int i;
>> +     int n;
>> +     bool notify = false;
>> +
>> +     if (!vqueue)
>> +             return -EIO;
>> +
>> +     i = (substream->msg_last_enqueued + 1) % runtime->periods;
>> +     n = runtime->periods - atomic_read(&substream->msg_count);
>> +
>> +     for (; n; --n, i = (i + 1) % runtime->periods) {
>> +             struct virtio_pcm_msg *msg = &substream->msgs[i];
>> +             struct scatterlist *psgs[PCM_MSG_SG_MAX] = {
>> +                     [PCM_MSG_SG_XFER] = &msg->sgs[PCM_MSG_SG_XFER],
>> +                     [PCM_MSG_SG_DATA] = &msg->sgs[PCM_MSG_SG_DATA],
>> +                     [PCM_MSG_SG_STATUS] = &msg->sgs[PCM_MSG_SG_STATUS]
>> +             };
>> +             int rc;
>> +
>> +             msg->xfer.stream_id = cpu_to_virtio32(vdev, substream->sid);
>> +             memset(&msg->status, 0, sizeof(msg->status));
>> +
>> +             atomic_inc(&substream->msg_count);
>> +
>> +             if (substream->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) {
>> +                     atomic_dec(&substream->msg_count);
>> +                     return -EIO;
>> +             }
>> +
>> +             substream->msg_last_enqueued = i;
>> +     }
>> +
>> +     if (!(substream->features & (1U << VIRTIO_SND_PCM_F_MSG_POLLING)))
>> +             notify = virtqueue_kick_prepare(vqueue);
>> +
>> +     if (notify)
>> +             if (!virtqueue_notify(vqueue))
>> +                     return -EIO;
>> +
>> +     return 0;
>> +}
>> +
>> +/**
>> + * virtsnd_pcm_msg_complete() - Complete an I/O message.
>> + * @msg: I/O message.
>> + * @size: Number of bytes written.
>> + *
>> + * Completion of the message means the elapsed period:
>> + *   - update hardware pointer,
>> + *   - update latency value,
>> + *   - kick the upper layer.
>> + *
>> + * Context: Interrupt context.
>> + */
>> +static void virtsnd_pcm_msg_complete(struct virtio_pcm_msg *msg, size_t size)
>> +{
>> +     struct virtio_pcm_substream *substream = msg->substream;
>> +     snd_pcm_uframes_t hw_ptr;
>> +     unsigned int msg_count;
>> +
>> +     hw_ptr = (snd_pcm_uframes_t)atomic_read(&substream->hw_ptr);
>> +
>> +     /*
>> +      * If the capture substream returned an incorrect status, then just
>> +      * increase the hw_ptr by the period size.
>> +      */
>> +     if (substream->direction == SNDRV_PCM_STREAM_PLAYBACK ||
>> +         size <= sizeof(msg->status)) {
>> +             hw_ptr += substream->period_size;
>> +     } else {
>> +             size -= sizeof(msg->status);
>> +             hw_ptr += size / substream->frame_bytes;
>> +     }
>> +
>> +     atomic_set(&substream->hw_ptr, (u32)(hw_ptr % substream->buffer_size));
>> +     atomic_set(&substream->xfer_xrun, 0);
>> +
>> +     msg_count = atomic_dec_return(&substream->msg_count);
>> +
>> +     if (atomic_read(&substream->xfer_enabled)) {
>> +             struct snd_pcm_runtime *runtime = substream->substream->runtime;
>> +
>> +             runtime->delay =
>> +                     bytes_to_frames(runtime,
>> +                                     le32_to_cpu(msg->status.latency_bytes));
>> +
>> +             snd_pcm_period_elapsed(substream->substream);
>> +
>> +             virtsnd_pcm_msg_send(substream);
>> +     } else if (!msg_count) {
>> +             wake_up_all(&substream->msg_empty);
>> +     }
>> +}
>> +
>> +/**
>> + * virtsnd_pcm_notify_cb() - Process all completed I/O messages.
>> + * @vqueue: Underlying tx/rx virtqueue.
>> + *
>> + * If transmission is allowed, then each completed message is immediately placed
>> + * back at the end of the queue.
>> + *
>> + * Context: Interrupt context. Takes and releases the tx/rx queue spinlock.
>> + */
>> +static inline void virtsnd_pcm_notify_cb(struct virtio_snd_queue *queue)
>> +{
>> +     unsigned long flags;
>> +
>> +     spin_lock_irqsave(&queue->lock, flags);
>> +     while (queue->vqueue) {
>> +             virtqueue_disable_cb(queue->vqueue);
>> +
>> +             for (;;) {
>> +                     struct virtio_pcm_msg *msg;
>> +                     u32 length;
>> +
>> +                     msg = virtqueue_get_buf(queue->vqueue, &length);
>> +                     if (!msg)
>> +                             break;
>> +
>> +                     virtsnd_pcm_msg_complete(msg, length);
>> +             }
>> +
>> +             if (unlikely(virtqueue_is_broken(queue->vqueue)))
>> +                     break;
>> +
>> +             if (virtqueue_enable_cb(queue->vqueue))
>> +                     break;
>> +     }
>> +     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.
>> + * @substream: 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, ERR_PTR(-errno) on failure.
>> + */
>> +struct virtio_snd_msg *
>> +virtsnd_pcm_ctl_msg_alloc(struct virtio_pcm_substream *substream,
>> +                       unsigned int command, gfp_t gfp)
>> +{
>> +     struct virtio_device *vdev = substream->snd->vdev;
>> +     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(vdev, request_size, response_size, gfp);
>> +     if (!IS_ERR(msg)) {
>> +             struct virtio_snd_pcm_hdr *hdr = sg_virt(&msg->sg_request);
>> +
>> +             hdr->hdr.code = cpu_to_virtio32(vdev, command);
>> +             hdr->stream_id = cpu_to_virtio32(vdev, substream->sid);
>> +     }
>> +
>> +     return msg;
>> +}
>> --
>> 2.30.0
>>
>>
> 
> 

-- 
Anton Yakovlev
Senior Software Engineer

OpenSynergy GmbH
Rotherstr. 20, 10245 Berlin

Phone: +49 30 60 98 54 0
E-Mail: anton.yakovlev@opensynergy.com

www.opensynergy.com

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