Matias Ezequiel Vara Larsen
2023-Oct-17 12:45 UTC
[RFC PATCH] ALSA: virtio: use copy and fill_silence callbacks
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 at 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... >