[PATCH RFC] vhost: add an SOF Audio DSP driver

[PATCH RFC] vhost: add an SOF Audio DSP driver

[Guennadi Liakhovetski]

The SOF ADSP vhost driver consists of two parts: a sound and a vhost
part. This patch implements the vhost part of the driver. It handles
QEMU communication with the vhost misc device and virtual queues to
any VirtIO RPMsg guests.

Signed-off-by: Guennadi Liakhovetski <guennadi.liakhovetski@linux.intel.com>
---

This is marked as an RFC / request for review, since it depends on other
patches, that haven't been merged yet. It uses the vhost RPMsg API, submitted
minutes ago to the lists
https://lists.linuxfoundation.org/pipermail/virtualization/2020-May/047669.html
and is a part of the SOF virtualisation project
https://github.com/thesofproject/linux/pull/1501/commits

Thanks
Guennadi

 drivers/vhost/Kconfig  |  10 +
 drivers/vhost/Makefile |   3 +
 drivers/vhost/adsp.c   | 618 +++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 631 insertions(+)
 create mode 100644 drivers/vhost/adsp.c

diff --git a/drivers/vhost/Kconfig b/drivers/vhost/Kconfig
index 4021522..2aff7c1 100644
--- a/drivers/vhost/Kconfig
+++ b/drivers/vhost/Kconfig
@@ -28,6 +28,16 @@ config VHOST_SCSI
 	Say M here to enable the vhost_scsi TCM fabric module
 	for use with virtio-scsi guests
 
+config VHOST_SOF
+	tristate "Vhost SOF driver"
+	depends on SND_SOC_SOF
+	select VHOST
+	select VHOST_RPMSG
+	default n
+	---help---
+	  SOF vhost VirtIO driver. It exports the same IPC interface, as the
+	  one, used for Audio DSP communication, to Linux VirtIO guests.
+
 config VHOST_VSOCK
 	tristate "vhost virtio-vsock driver"
 	depends on VSOCKETS && EVENTFD
diff --git a/drivers/vhost/Makefile b/drivers/vhost/Makefile
index 29b8115..3de5e08 100644
--- a/drivers/vhost/Makefile
+++ b/drivers/vhost/Makefile
@@ -8,6 +8,9 @@ vhost_rpmsg-y := rpmsg.o
 obj-$(CONFIG_VHOST_SCSI) += vhost_scsi.o
 vhost_scsi-y := scsi.o
 
+obj-$(CONFIG_VHOST_SOF) += vhost_sof.o
+vhost_sof-y := adsp.o
+
 obj-$(CONFIG_VHOST_VSOCK) += vhost_vsock.o
 vhost_vsock-y := vsock.o
 
diff --git a/drivers/vhost/adsp.c b/drivers/vhost/adsp.c
new file mode 100644
index 00000000..c386cf3
--- /dev/null
+++ b/drivers/vhost/adsp.c
@@ -0,0 +1,618 @@
+/* SPDX-License-Identifier: (GPL-2.0 OR BSD-3-Clause) */
+/*
+ * Copyright(c) 2019-2020 Intel Corporation. All rights reserved.
+ *
+ * Author: Guennadi Liakhovetski <guennadi.liakhovetski@linux.intel.com>
+ *
+ * vhost-SOF VirtIO interface
+ */
+
+#include <linux/bitmap.h>
+#include <linux/compat.h>
+#include <linux/file.h>
+#include <linux/miscdevice.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/slab.h>
+#include <linux/spinlock.h>
+#include <linux/vhost.h>
+#include <linux/virtio_rpmsg.h>
+#include <uapi/linux/rpmsg.h>
+
+#include <sound/sof/stream.h>
+#include <sound/sof/rpmsg.h>
+
+#include "vhost.h"
+#include "vhost_rpmsg.h"
+
+#define VHOST_DSP_FEATURES (VHOST_FEATURES | (1ULL << VIRTIO_RPMSG_F_NS))
+
+struct snd_sof_dev;
+struct sof_vhost_client;
+
+struct vhost_dsp {
+	struct vhost_rpmsg vrdev;
+
+	struct sof_vhost_client *snd;
+
+	bool active;
+
+	/* RPMsg address of the position update endpoint */
+	u32 posn_addr;
+	/* position update buffer and work */
+	struct vhost_work posn_work;
+	struct sof_ipc_stream_posn posn;
+
+	/* IPC request buffer */
+	struct sof_rpmsg_ipc_req ipc_buf;
+	/* IPC response buffer */
+	u8 reply_buf[SOF_IPC_MSG_MAX_SIZE];
+	/*
+	 * data response header, captured audio data is copied directly from the
+	 * DMA buffer
+	 */
+	struct sof_rpmsg_data_resp data_resp;
+};
+
+/* A guest is booting */
+static int vhost_dsp_activate(struct vhost_dsp *dsp)
+{
+	unsigned int i;
+	int ret = 0;
+
+	mutex_lock(&dsp->vrdev.dev.mutex);
+
+	/* Wait until all the VirtQueues have been initialised */
+	if (!dsp->active) {
+		struct vhost_virtqueue *vq;
+
+		for (i = 0, vq = dsp->vrdev.vq;
+		     i < ARRAY_SIZE(dsp->vrdev.vq);
+		     i++, vq++) {
+			/* .private_data is required != NULL */
+			vq->private_data = vq;
+			/* needed for re-initialisation upon guest reboot */
+			ret = vhost_vq_init_access(vq);
+			if (ret)
+				vq_err(vq,
+				       "%s(): error %d initialising vq #%d\n",
+				       __func__, ret, i);
+		}
+
+		/* Send an RPMsg namespace announcement */
+		if (!ret && !vhost_rpmsg_ns_announce(&dsp->vrdev, "sof_rpmsg",
+						     SOF_RPMSG_ADDR_IPC))
+			dsp->active = true;
+	}
+
+	mutex_unlock(&dsp->vrdev.dev.mutex);
+
+	return ret;
+}
+
+/* A guest is powered off or reset */
+static void vhost_dsp_deactivate(struct vhost_dsp *dsp)
+{
+	unsigned int i;
+
+	mutex_lock(&dsp->vrdev.dev.mutex);
+
+	if (dsp->active) {
+		struct vhost_virtqueue *vq;
+
+		dsp->active = false;
+
+		/* If a VM reboots sof_vhost_client_release() isn't called */
+		sof_vhost_topology_purge(dsp->snd);
+
+		/* signal, that we're inactive */
+		for (i = 0, vq = dsp->vrdev.vq;
+		     i < ARRAY_SIZE(dsp->vrdev.vq);
+		     i++, vq++) {
+			mutex_lock(&vq->mutex);
+			vq->private_data = NULL;
+			mutex_unlock(&vq->mutex);
+		}
+	}
+
+	mutex_unlock(&dsp->vrdev.dev.mutex);
+}
+
+/* No special features at the moment */
+static int vhost_dsp_set_features(struct vhost_dsp *dsp, u64 features)
+{
+	struct vhost_virtqueue *vq;
+	unsigned int i;
+
+	if (features & ~VHOST_DSP_FEATURES)
+		return -EOPNOTSUPP;
+
+	mutex_lock(&dsp->vrdev.dev.mutex);
+
+	if ((features & (1 << VHOST_F_LOG_ALL)) &&
+	    !vhost_log_access_ok(&dsp->vrdev.dev)) {
+		mutex_unlock(&dsp->vrdev.dev.mutex);
+		return -EFAULT;
+	}
+
+	for (i = 0, vq = dsp->vrdev.vq;
+	     i < ARRAY_SIZE(dsp->vrdev.vq);
+	     i++, vq++) {
+		mutex_lock(&vq->mutex);
+		vq->acked_features = features;
+		mutex_unlock(&vq->mutex);
+	}
+
+	mutex_unlock(&dsp->vrdev.dev.mutex);
+
+	return 0;
+}
+
+/* .ioctl(): we only use VHOST_SET_RUNNING in a non-default way */
+static long vhost_dsp_ioctl(struct file *filp, unsigned int ioctl,
+			    unsigned long arg)
+{
+	struct vhost_dsp *dsp = filp->private_data;
+	void __user *argp = (void __user *)arg;
+	struct vhost_adsp_topology tplg;
+	u64 __user *featurep = argp;
+	u64 features;
+	int start;
+	long ret;
+
+	switch (ioctl) {
+	case VHOST_GET_FEATURES:
+		features = VHOST_DSP_FEATURES;
+		if (copy_to_user(featurep, &features, sizeof(features)))
+			return -EFAULT;
+		return 0;
+	case VHOST_SET_FEATURES:
+		if (copy_from_user(&features, featurep, sizeof(features)))
+			return -EFAULT;
+		return vhost_dsp_set_features(dsp, features);
+	case VHOST_GET_BACKEND_FEATURES:
+		features = 0;
+		if (copy_to_user(featurep, &features, sizeof(features)))
+			return -EFAULT;
+		return 0;
+	case VHOST_SET_BACKEND_FEATURES:
+		if (copy_from_user(&features, featurep, sizeof(features)))
+			return -EFAULT;
+		if (features)
+			return -EOPNOTSUPP;
+		return 0;
+	case VHOST_RESET_OWNER:
+		mutex_lock(&dsp->vrdev.dev.mutex);
+		ret = vhost_dev_check_owner(&dsp->vrdev.dev);
+		if (!ret) {
+			struct vhost_umem *umem =
+				vhost_dev_reset_owner_prepare();
+			if (!umem) {
+				ret = -ENOMEM;
+			} else {
+				vhost_dev_stop(&dsp->vrdev.dev);
+				vhost_dev_reset_owner(&dsp->vrdev.dev, umem);
+			}
+		}
+		mutex_unlock(&dsp->vrdev.dev.mutex);
+		return ret;
+	case VHOST_SET_OWNER:
+		mutex_lock(&dsp->vrdev.dev.mutex);
+		ret = vhost_dev_set_owner(&dsp->vrdev.dev);
+		mutex_unlock(&dsp->vrdev.dev.mutex);
+		return ret;
+	case VHOST_SET_RUNNING:
+		if (copy_from_user(&start, argp, sizeof(start)))
+			return -EFAULT;
+
+		if (start)
+			return vhost_dsp_activate(dsp);
+
+		vhost_dsp_deactivate(dsp);
+		return 0;
+	case VHOST_ADSP_SET_GUEST_TPLG:
+		if (copy_from_user(&tplg, argp, sizeof(tplg)))
+			return -EFAULT;
+		return sof_vhost_set_tplg(dsp->snd, &tplg);
+	}
+
+	mutex_lock(&dsp->vrdev.dev.mutex);
+	ret = vhost_dev_ioctl(&dsp->vrdev.dev, ioctl, argp);
+	if (ret == -ENOIOCTLCMD)
+		ret = vhost_vring_ioctl(&dsp->vrdev.dev, ioctl, argp);
+	mutex_unlock(&dsp->vrdev.dev.mutex);
+
+	return ret;
+}
+
+#ifdef CONFIG_COMPAT
+static long vhost_dsp_compat_ioctl(struct file *filp, unsigned int ioctl,
+				   unsigned long arg)
+{
+	return vhost_dsp_ioctl(filp, ioctl, (unsigned long)compat_ptr(arg));
+}
+#endif
+
+static ssize_t vhost_dsp_chr_read_iter(struct kiocb *iocb, struct iov_iter *to)
+{
+	struct file *filp = iocb->ki_filp;
+	struct vhost_dsp *dsp = filp->private_data;
+	struct vhost_dev *dev = &dsp->vrdev.dev;
+	int noblock = filp->f_flags & O_NONBLOCK;
+
+	return vhost_chr_read_iter(dev, to, noblock);
+}
+
+static ssize_t vhost_dsp_chr_write_iter(struct kiocb *iocb,
+					struct iov_iter *from)
+{
+	struct file *filp = iocb->ki_filp;
+	struct vhost_dsp *dsp = filp->private_data;
+	struct vhost_dev *dev = &dsp->vrdev.dev;
+
+	return vhost_chr_write_iter(dev, from);
+}
+
+static __poll_t vhost_dsp_chr_poll(struct file *filp, poll_table *wait)
+{
+	struct vhost_dsp *dsp = filp->private_data;
+	struct vhost_dev *dev = &dsp->vrdev.dev;
+
+	return vhost_chr_poll(filp, dev, wait);
+}
+
+static ssize_t vhost_dsp_data_read(struct vhost_rpmsg *vr,
+				   struct vhost_rpmsg_iter *iter)
+{
+	struct vhost_dsp *dsp = container_of(vr, struct vhost_dsp, vrdev);
+	struct vhost_virtqueue *vq = iter->vq;
+	struct sof_rpmsg_data_resp *resp = &dsp->data_resp;
+	struct sof_rpmsg_data_req req;
+	size_t len = vhost_rpmsg_iter_len(iter);
+	size_t nbytes;
+
+	if (len < sizeof(req)) {
+		vq_err(vq, "%s(): data count %zu too small\n",
+		       __func__, len);
+		return -EINVAL;
+	}
+
+	/* copy_{to,from}_iter() can be called repeatedly to continue copying */
+	nbytes = vhost_rpmsg_copy(vr, iter, &req, sizeof(req));
+	if (nbytes != sizeof(req)) {
+		vq_err(vq,
+		       "%s(): got %zu instead of %zu bytes of data header\n",
+		       __func__, nbytes, sizeof(req));
+		return -EIO;
+	}
+
+	len -= nbytes;
+
+	/* Get a pointer to copy data to or from the audio buffer */
+	iter->priv = sof_vhost_stream_data(dsp->snd, &req, resp);
+	if (IS_ERR(iter->priv)) {
+		vq_err(vq, "%s(): error %ld getting data pointer\n",
+		       __func__, PTR_ERR(iter->priv));
+		return PTR_ERR(iter->priv);
+	}
+
+	if (len) {
+		/* Data in the buffer: playback */
+		if (len != req.size) {
+			vq_err(vq,
+			       "%s(): inconsistent data count: %zu vs. %u bytes\n",
+			       __func__, len, req.size);
+			return -EPROTO;
+		}
+
+		nbytes = vhost_rpmsg_copy(vr, iter, iter->priv, len);
+		if (nbytes != len) {
+			vq_err(vq,
+			       "%s(): copied %zu instead of %zu bytes of data\n",
+			       __func__, nbytes, len);
+			return -EIO;
+		}
+
+		return sizeof(*resp);
+	}
+
+	return sizeof(*resp) + resp->size;
+}
+
+static ssize_t vhost_dsp_data_write(struct vhost_rpmsg *vr,
+				    struct vhost_rpmsg_iter *iter)
+{
+	struct vhost_dsp *dsp = container_of(vr, struct vhost_dsp, vrdev);
+	struct vhost_virtqueue *vq = iter->vq;
+	struct sof_rpmsg_data_resp *resp = &dsp->data_resp;
+	size_t len = vhost_rpmsg_iter_len(iter);
+	size_t nbytes;
+
+	if (len < sizeof(*resp)) {
+		vq_err(vq,
+		       "%s(): %zu bytes aren't enough for %zu bytes of header\n",
+		       __func__, len, sizeof(*resp));
+		return -ENOBUFS;
+	}
+
+	nbytes = vhost_rpmsg_copy(vr, iter, resp, sizeof(*resp));
+	if (nbytes != sizeof(*resp)) {
+		vq_err(vq,
+		       "%s(): copied %zu instead of %zu bytes of data\n",
+		       __func__, nbytes, sizeof(*resp));
+		return -EIO;
+	}
+
+	if (resp->size && !resp->error) {
+		/* Capture */
+		len -= sizeof(*resp);
+
+		if (len < resp->size) {
+			vq_err(vq,
+			       "%s(): insufficient buffer space %zu for %u bytes\n",
+			       __func__, len, resp->size);
+			return -EPROTO;
+		}
+
+		nbytes = vhost_rpmsg_copy(vr, iter, iter->priv, resp->size);
+		if (nbytes != resp->size) {
+			vq_err(vq,
+			       "%s(): copied %zu instead of %u bytes of data\n",
+			       __func__, nbytes, resp->size);
+			return -EIO;
+		}
+	}
+
+	return 0;
+}
+
+static ssize_t vhost_dsp_ipc_read(struct vhost_rpmsg *vr,
+				  struct vhost_rpmsg_iter *iter)
+{
+	struct vhost_dsp *dsp = container_of(vr, struct vhost_dsp, vrdev);
+	struct vhost_virtqueue *vq = iter->vq;
+	size_t len = vhost_rpmsg_iter_len(iter);
+	size_t nbytes;
+	int ret;
+
+	if (len > sizeof(dsp->ipc_buf)) {
+		vq_err(vq, "%s(): data count %zu too large\n",
+		       __func__, len);
+		return -ENOBUFS;
+	}
+
+	if (len < sizeof(struct sof_ipc_cmd_hdr)) {
+		vq_err(vq, "%s(): data count %zu too small\n",
+		       __func__, len);
+		return -EINVAL;
+	}
+
+	nbytes = vhost_rpmsg_copy(vr, iter, &dsp->ipc_buf, len);
+	if (nbytes != len) {
+		vq_err(vq, "Expected %zu bytes for IPC, got %zu bytes\n",
+		       len, nbytes);
+		return -EIO;
+	}
+
+	/* Process the IPC payload */
+	ret = sof_vhost_ipc_fwd(dsp->snd, dsp->ipc_buf.ipc_msg,
+				dsp->reply_buf, len -
+				offsetof(struct sof_rpmsg_ipc_req, ipc_msg),
+				dsp->ipc_buf.reply_size);
+	if (ret < 0) {
+		struct sof_ipc_cmd_hdr *cmd_hdr =
+			(struct sof_ipc_cmd_hdr *)dsp->ipc_buf.ipc_msg;
+		vq_err(vq, "%s(): IPC 0x%x failed with error %d\n",
+		       __func__, cmd_hdr->cmd, ret);
+		/* continue to send an error response */
+	}
+
+	return ((struct sof_ipc_reply *)dsp->reply_buf)->hdr.size;
+}
+
+static ssize_t vhost_dsp_ipc_write(struct vhost_rpmsg *vr,
+				   struct vhost_rpmsg_iter *iter)
+{
+	struct vhost_dsp *dsp = container_of(vr, struct vhost_dsp, vrdev);
+
+	return vhost_rpmsg_copy(vr, iter, dsp->reply_buf,
+				vhost_rpmsg_iter_len(iter)) ==
+		vhost_rpmsg_iter_len(iter) ? 0 : -EIO;
+}
+
+/* Called only once to get guest's position update endpoint address */
+static ssize_t vhost_dsp_posn_read(struct vhost_rpmsg *vr,
+				   struct vhost_rpmsg_iter *iter)
+{
+	struct vhost_dsp *dsp = container_of(vr, struct vhost_dsp, vrdev);
+	struct vhost_virtqueue *vq = &dsp->vrdev.vq[VIRTIO_RPMSG_REQUEST];
+	size_t len = vhost_rpmsg_iter_len(iter);
+	size_t nbytes;
+
+	if ((int)dsp->posn_addr >= 0) {
+		vq_err(vq, "%s(): position queue address %u already set\n",
+		       __func__, dsp->posn_addr);
+		return -EINVAL;
+	}
+
+	if (len != sizeof(dsp->posn_addr)) {
+		vq_err(vq, "%s(): data count %zu invalid\n",
+		       __func__, len);
+		return -EINVAL;
+	}
+
+	nbytes = vhost_rpmsg_copy(vr, iter, &dsp->posn_addr,
+				  sizeof(dsp->posn_addr));
+	if (nbytes != sizeof(dsp->posn_addr)) {
+		vq_err(vq,
+		       "%s(): got %zu instead of %zu bytes position update\n",
+		       __func__, nbytes, sizeof(dsp->posn_addr));
+		return -EIO;
+	}
+
+	pr_debug("%s(): guest position endpoint address 0x%x\n", __func__,
+		 dsp->posn_addr);
+
+	return 0;
+}
+
+static void vhost_dsp_send_posn(struct vhost_work *work)
+{
+	struct vhost_dsp *dsp = container_of(work, struct vhost_dsp, posn_work);
+	struct vhost_rpmsg_iter iter = VHOST_RPMSG_ITER(SOF_RPMSG_ADDR_POSN,
+							dsp->posn_addr);
+	ssize_t nbytes;
+	int ret;
+
+	ret = vhost_rpmsg_start_lock(&dsp->vrdev, &iter, VIRTIO_RPMSG_RESPONSE,
+				     sizeof(dsp->posn));
+	if (ret < 0)
+		return;
+
+	nbytes = vhost_rpmsg_copy(&dsp->vrdev, &iter, &dsp->posn,
+				  sizeof(dsp->posn));
+	if (nbytes != sizeof(dsp->posn))
+		vq_err(iter.vq, "%s(): added %zd instead of %zu bytes\n",
+		       __func__, nbytes, sizeof(dsp->posn));
+
+	ret = vhost_rpmsg_finish_unlock(&dsp->vrdev, &iter);
+}
+
+static const struct vhost_rpmsg_ept vhost_dsp_ept[] = {
+	{
+		.addr = SOF_RPMSG_ADDR_IPC,
+		.read = vhost_dsp_ipc_read,
+		.write = vhost_dsp_ipc_write,
+	}, {
+		.addr = SOF_RPMSG_ADDR_POSN,
+		.read = vhost_dsp_posn_read,
+		.write = NULL, /* position updates are sent from a work-queue */
+	}, {
+		.addr = SOF_RPMSG_ADDR_DATA,
+		.read = vhost_dsp_data_read,
+		.write = vhost_dsp_data_write,
+	}
+};
+
+static int vhost_dsp_open(struct inode *inode, struct file *filp)
+{
+	struct miscdevice *misc = filp->private_data;
+	struct snd_sof_dev *sdev = dev_get_drvdata(misc->parent);
+	struct vhost_dsp *dsp = kmalloc(sizeof(*dsp), GFP_KERNEL);
+
+	if (!dsp)
+		return -ENOMEM;
+
+	dsp->vrdev.dev.mm = NULL;
+	dsp->snd = sof_vhost_client_add(sdev, dsp);
+	if (!dsp->snd) {
+		kfree(dsp);
+		return -ENOMEM;
+	}
+
+	/*
+	 * TODO: do we ever want to support multiple guest machines per DSP, if
+	 * not, we might as well perform all allocations when registering the
+	 * misc device.
+	 */
+	dsp->active = false;
+	dsp->posn_addr = -EINVAL;
+	dsp->posn.rhdr.error = -ENODATA;
+
+	vhost_rpmsg_init(&dsp->vrdev, vhost_dsp_ept, ARRAY_SIZE(vhost_dsp_ept));
+	vhost_work_init(&dsp->posn_work, vhost_dsp_send_posn);
+
+	/* Overwrite file private data */
+	filp->private_data = dsp;
+
+	return 0;
+}
+
+/*
+ * The device is closed by QEMU when the client driver is unloaded or the guest
+ * is shut down
+ */
+static int vhost_dsp_release(struct inode *inode, struct file *filp)
+{
+	struct vhost_dsp *dsp = filp->private_data;
+
+	vhost_work_flush(&dsp->vrdev.dev, &dsp->posn_work);
+
+	vhost_rpmsg_destroy(&dsp->vrdev);
+
+	sof_vhost_client_release(dsp->snd);
+
+	kfree(dsp);
+
+	return 0;
+}
+
+static const struct file_operations vhost_dsp_fops = {
+	.owner          = THIS_MODULE,
+	.release        = vhost_dsp_release,
+	.read_iter      = vhost_dsp_chr_read_iter,
+	.write_iter     = vhost_dsp_chr_write_iter,
+	.poll           = vhost_dsp_chr_poll,
+	.unlocked_ioctl = vhost_dsp_ioctl,
+#ifdef CONFIG_COMPAT
+	.compat_ioctl   = vhost_dsp_compat_ioctl,
+#endif
+	.open           = vhost_dsp_open,
+	.llseek		= noop_llseek,
+};
+
+static struct miscdevice vhost_dsp_misc = {
+	.minor = MISC_DYNAMIC_MINOR,
+	.name = "vhost-dsp",
+	.fops = &vhost_dsp_fops,
+};
+
+/* Always called from an interrupt thread context */
+static int vhost_dsp_update_posn(struct vhost_dsp *dsp,
+				 struct sof_ipc_stream_posn *posn)
+{
+	struct vhost_virtqueue *vq = &dsp->vrdev.vq[VIRTIO_RPMSG_RESPONSE];
+	int ret;
+
+	if (!dsp->active)
+		return 0;
+
+	memcpy(&dsp->posn, posn, sizeof(dsp->posn));
+
+	mutex_lock(&vq->mutex);
+
+	/*
+	 * VirtQueues can only be processed in the context of the VMM process or
+	 * a vhost work queue
+	 */
+	vhost_work_queue(&dsp->vrdev.dev, &dsp->posn_work);
+
+	mutex_unlock(&vq->mutex);
+
+	return ret;
+}
+
+static struct sof_vhost_ops vhost_dsp_ops = {
+	.update_posn = vhost_dsp_update_posn,
+};
+
+static int __init vhost_dsp_init(void)
+{
+	vhost_dsp_misc.parent = sof_vhost_dev_init(&vhost_dsp_ops);
+	if (!vhost_dsp_misc.parent)
+		return -ENODEV;
+
+	return misc_register(&vhost_dsp_misc);
+}
+
+static void __exit vhost_dsp_exit(void)
+{
+	misc_deregister(&vhost_dsp_misc);
+}
+
+module_init(vhost_dsp_init);
+module_exit(vhost_dsp_exit);
+
+MODULE_LICENSE("Dual BSD/GPL");
+MODULE_AUTHOR("Guennadi Liakhovetski");
+MODULE_DESCRIPTION("Host kernel accelerator for virtio sound");
-- 
1.9.3

Re: [Sound-open-firmware] [PATCH RFC] vhost: add an SOF Audio DSP driver

[Pierre-Louis Bossart]

> +config VHOST_SOF
> +	tristate "Vhost SOF driver"
> +	depends on SND_SOC_SOF

you probably want to make sure VHOST_SOF and SND_SOC_SOF are both 
built-in or module. Without constraints you are likely to trigger errors 
with randconfig. It's a classic.

> +	select VHOST
> +	select VHOST_RPMSG
> +	default n

not needed, default is always no.

> +	---help---
> +	  SOF vhost VirtIO driver. It exports the same IPC interface, as the
> +	  one, used for Audio DSP communication, to Linux VirtIO guests.

[...]

> +struct vhost_dsp {
> +	struct vhost_rpmsg vrdev;
> +
> +	struct sof_vhost_client *snd;
> +
> +	bool active;

I am struggling with this definition, it seems to be a local flag but 
how is it aligned to the actual DSP status?
In other words, can you have cases where the dsp is considered 'active' 
here but might be pm_runtime suspended?
I am sure you've thought of it based on previous threads, it'd be worth 
adding comments.

> +
> +	/* RPMsg address of the position update endpoint */
> +	u32 posn_addr;
> +	/* position update buffer and work */
> +	struct vhost_work posn_work;
> +	struct sof_ipc_stream_posn posn;
> +
> +	/* IPC request buffer */
> +	struct sof_rpmsg_ipc_req ipc_buf;
> +	/* IPC response buffer */
> +	u8 reply_buf[SOF_IPC_MSG_MAX_SIZE];
> +	/*
> +	 * data response header, captured audio data is copied directly from the
> +	 * DMA buffer

so zero-copy is not supported for now, right?

> +	 */
> +	struct sof_rpmsg_data_resp data_resp;
> +};
> +
> +/* A guest is booting */
> +static int vhost_dsp_activate(struct vhost_dsp *dsp)
> +{
> +	unsigned int i;
> +	int ret = 0;
> +
> +	mutex_lock(&dsp->vrdev.dev.mutex);
> +
> +	/* Wait until all the VirtQueues have been initialised */
> +	if (!dsp->active) {
> +		struct vhost_virtqueue *vq;
> +
> +		for (i = 0, vq = dsp->vrdev.vq;
> +		     i < ARRAY_SIZE(dsp->vrdev.vq);
> +		     i++, vq++) {
> +			/* .private_data is required != NULL */
> +			vq->private_data = vq;
> +			/* needed for re-initialisation upon guest reboot */
> +			ret = vhost_vq_init_access(vq);
> +			if (ret)
> +				vq_err(vq,
> +				       "%s(): error %d initialising vq #%d\n",
> +				       __func__, ret, i);
> +		}
> +
> +		/* Send an RPMsg namespace announcement */
> +		if (!ret && !vhost_rpmsg_ns_announce(&dsp->vrdev, "sof_rpmsg",
> +						     SOF_RPMSG_ADDR_IPC))
> +			dsp->active = true;
> +	}
> +
> +	mutex_unlock(&dsp->vrdev.dev.mutex);
> +
> +	return ret;
> +}
> +
> +/* A guest is powered off or reset */
> +static void vhost_dsp_deactivate(struct vhost_dsp *dsp)
> +{
> +	unsigned int i;
> +
> +	mutex_lock(&dsp->vrdev.dev.mutex);
> +
> +	if (dsp->active) {
> +		struct vhost_virtqueue *vq;
> +
> +		dsp->active = false;

can you explain why this is not symmetrical with _activate above: there 
is no rmpsg communication here?

> +
> +		/* If a VM reboots sof_vhost_client_release() isn't called */
> +		sof_vhost_topology_purge(dsp->snd);
> +
> +		/* signal, that we're inactive */
> +		for (i = 0, vq = dsp->vrdev.vq;
> +		     i < ARRAY_SIZE(dsp->vrdev.vq);
> +		     i++, vq++) {
> +			mutex_lock(&vq->mutex);
> +			vq->private_data = NULL;
> +			mutex_unlock(&vq->mutex);
> +		}
> +	}
> +
> +	mutex_unlock(&dsp->vrdev.dev.mutex);
> +}
> +

[...]

> +/* .ioctl(): we only use VHOST_SET_RUNNING in a non-default way */
> +static long vhost_dsp_ioctl(struct file *filp, unsigned int ioctl,
> +			    unsigned long arg)
> +{
> +	struct vhost_dsp *dsp = filp->private_data;
> +	void __user *argp = (void __user *)arg;
> +	struct vhost_adsp_topology tplg;
> +	u64 __user *featurep = argp;
> +	u64 features;
> +	int start;
> +	long ret;
> +
> +	switch (ioctl) {
> +	case VHOST_GET_FEATURES:
> +		features = VHOST_DSP_FEATURES;
> +		if (copy_to_user(featurep, &features, sizeof(features)))
> +			return -EFAULT;
> +		return 0;
> +	case VHOST_SET_FEATURES:
> +		if (copy_from_user(&features, featurep, sizeof(features)))
> +			return -EFAULT;
> +		return vhost_dsp_set_features(dsp, features);
> +	case VHOST_GET_BACKEND_FEATURES:
> +		features = 0;
> +		if (copy_to_user(featurep, &features, sizeof(features)))
> +			return -EFAULT;
> +		return 0;
> +	case VHOST_SET_BACKEND_FEATURES:
> +		if (copy_from_user(&features, featurep, sizeof(features)))
> +			return -EFAULT;
> +		if (features)
> +			return -EOPNOTSUPP;
> +		return 0;
> +	case VHOST_RESET_OWNER:
> +		mutex_lock(&dsp->vrdev.dev.mutex);
> +		ret = vhost_dev_check_owner(&dsp->vrdev.dev);
> +		if (!ret) {
> +			struct vhost_umem *umem =
> +				vhost_dev_reset_owner_prepare();
> +			if (!umem) {
> +				ret = -ENOMEM;
> +			} else {
> +				vhost_dev_stop(&dsp->vrdev.dev);
> +				vhost_dev_reset_owner(&dsp->vrdev.dev, umem);
> +			}
> +		}
> +		mutex_unlock(&dsp->vrdev.dev.mutex);
> +		return ret;
> +	case VHOST_SET_OWNER:
> +		mutex_lock(&dsp->vrdev.dev.mutex);
> +		ret = vhost_dev_set_owner(&dsp->vrdev.dev);
> +		mutex_unlock(&dsp->vrdev.dev.mutex);
> +		return ret;
> +	case VHOST_SET_RUNNING:
> +		if (copy_from_user(&start, argp, sizeof(start)))
> +			return -EFAULT;
> +
> +		if (start)
> +			return vhost_dsp_activate(dsp);
> +
> +		vhost_dsp_deactivate(dsp);
> +		return 0;
> +	case VHOST_ADSP_SET_GUEST_TPLG:
> +		if (copy_from_user(&tplg, argp, sizeof(tplg)))
> +			return -EFAULT;
> +		return sof_vhost_set_tplg(dsp->snd, &tplg);
> +	}

All cases seem to use return, so the the code below seems to be the 
default: case?

> +	mutex_lock(&dsp->vrdev.dev.mutex);
> +	ret = vhost_dev_ioctl(&dsp->vrdev.dev, ioctl, argp);
> +	if (ret == -ENOIOCTLCMD)
> +		ret = vhost_vring_ioctl(&dsp->vrdev.dev, ioctl, argp);
> +	mutex_unlock(&dsp->vrdev.dev.mutex);
> +
> +	return ret;
> +}

[...]

> +static ssize_t vhost_dsp_ipc_write(struct vhost_rpmsg *vr,
> +				   struct vhost_rpmsg_iter *iter)
> +{
> +	struct vhost_dsp *dsp = container_of(vr, struct vhost_dsp, vrdev);
> +
> +	return vhost_rpmsg_copy(vr, iter, dsp->reply_buf,
> +				vhost_rpmsg_iter_len(iter)) ==
> +		vhost_rpmsg_iter_len(iter) ? 0 : -EIO;
> +}

This is rather convoluted code, with the same function called on both 
sides of a comparison.

> +
> +/* Called only once to get guest's position update endpoint address */
> +static ssize_t vhost_dsp_posn_read(struct vhost_rpmsg *vr,
> +				   struct vhost_rpmsg_iter *iter)
> +{
> +	struct vhost_dsp *dsp = container_of(vr, struct vhost_dsp, vrdev);
> +	struct vhost_virtqueue *vq = &dsp->vrdev.vq[VIRTIO_RPMSG_REQUEST];
> +	size_t len = vhost_rpmsg_iter_len(iter);
> +	size_t nbytes;
> +
> +	if ((int)dsp->posn_addr >= 0) {

posn_addr is defined as a u32, so what are you trying to test here?

> +		vq_err(vq, "%s(): position queue address %u already set\n",
> +		       __func__, dsp->posn_addr);
> +		return -EINVAL;
> +	}
> +
> +	if (len != sizeof(dsp->posn_addr)) {

that also seems suspicious:

+	/* RPMsg address of the position update endpoint */
+	u32 posn_addr;

why would a length which should have different values have anything to 
do with a constant 4 bytes?

> +		vq_err(vq, "%s(): data count %zu invalid\n",
> +		       __func__, len);
> +		return -EINVAL;
> +	}
> +
> +	nbytes = vhost_rpmsg_copy(vr, iter, &dsp->posn_addr,
> +				  sizeof(dsp->posn_addr));
> +	if (nbytes != sizeof(dsp->posn_addr)) {

and again here?

> +		vq_err(vq,
> +		       "%s(): got %zu instead of %zu bytes position update\n",
> +		       __func__, nbytes, sizeof(dsp->posn_addr));
> +		return -EIO;
> +	}
> +
> +	pr_debug("%s(): guest position endpoint address 0x%x\n", __func__,
> +		 dsp->posn_addr);
> +
> +	return 0;
> +}
> +

[...]

> +static int vhost_dsp_open(struct inode *inode, struct file *filp)
> +{
> +	struct miscdevice *misc = filp->private_data;
> +	struct snd_sof_dev *sdev = dev_get_drvdata(misc->parent);
> +	struct vhost_dsp *dsp = kmalloc(sizeof(*dsp), GFP_KERNEL);
> +
> +	if (!dsp)
> +		return -ENOMEM;
> +
> +	dsp->vrdev.dev.mm = NULL;
> +	dsp->snd = sof_vhost_client_add(sdev, dsp);
> +	if (!dsp->snd) {
> +		kfree(dsp);
> +		return -ENOMEM;
> +	}
> +
> +	/*
> +	 * TODO: do we ever want to support multiple guest machines per DSP, if

That is a basic assumption yes.

> +	 * not, we might as well perform all allocations when registering the
> +	 * misc device.
> +	 */
> +	dsp->active = false;
> +	dsp->posn_addr = -EINVAL;
> +	dsp->posn.rhdr.error = -ENODATA;
> +
> +	vhost_rpmsg_init(&dsp->vrdev, vhost_dsp_ept, ARRAY_SIZE(vhost_dsp_ept));
> +	vhost_work_init(&dsp->posn_work, vhost_dsp_send_posn);
> +
> +	/* Overwrite file private data */
> +	filp->private_data = dsp;
> +
> +	return 0;
> +}

[...]

> +/* Always called from an interrupt thread context */
> +static int vhost_dsp_update_posn(struct vhost_dsp *dsp,
> +				 struct sof_ipc_stream_posn *posn)
> +{
> +	struct vhost_virtqueue *vq = &dsp->vrdev.vq[VIRTIO_RPMSG_RESPONSE];
> +	int ret;
> +
> +	if (!dsp->active)
> +		return 0;

is there a case where you can get a position update without the dsp 
being active?
And shouldn't this be an error?
> +
> +	memcpy(&dsp->posn, posn, sizeof(dsp->posn));
> +
> +	mutex_lock(&vq->mutex);
> +
> +	/*
> +	 * VirtQueues can only be processed in the context of the VMM process or
> +	 * a vhost work queue
> +	 */
> +	vhost_work_queue(&dsp->vrdev.dev, &dsp->posn_work);
> +
> +	mutex_unlock(&vq->mutex);
> +
> +	return ret;

Re: [Sound-open-firmware] [PATCH RFC] vhost: add an SOF Audio DSP driver

[Guennadi Liakhovetski]

Hi Pierre,

Thanks for the review!

On Sat, May 16, 2020 at 11:50:48AM -0500, Pierre-Louis Bossart wrote:
> 
> 
> 
> > +config VHOST_SOF
> > +	tristate "Vhost SOF driver"
> > +	depends on SND_SOC_SOF
> 
> you probably want to make sure VHOST_SOF and SND_SOC_SOF are both built-in
> or module. Without constraints you are likely to trigger errors with
> randconfig. It's a classic.

"depends on" guarantees, that I cannot build VHOST_SOF into the kernel while 
SND_SOC_SOF is configured as a module and that I cannot enable VHOST_SOF 
while SND_SOC_SOF is disabled, isn't it enough? Is there a problem if 
VHOST_SOF is a module and SND_SOC_SOF is built into the kernel?

> > +	select VHOST
> > +	select VHOST_RPMSG
> > +	default n
> 
> not needed, default is always no.

Ok, thanks, will remove.

> > +	---help---
> > +	  SOF vhost VirtIO driver. It exports the same IPC interface, as the
> > +	  one, used for Audio DSP communication, to Linux VirtIO guests.
> 
> [...]
> 
> > +struct vhost_dsp {
> > +	struct vhost_rpmsg vrdev;
> > +
> > +	struct sof_vhost_client *snd;
> > +
> > +	bool active;
> 
> I am struggling with this definition, it seems to be a local flag but how is
> it aligned to the actual DSP status?
> In other words, can you have cases where the dsp is considered 'active' here
> but might be pm_runtime suspended?
> I am sure you've thought of it based on previous threads, it'd be worth
> adding comments.

Yes, it might be a bit confusing, I'll add comments. This flag has nothing to 
do with the DSP state. Its purpose is to track reboots of the client, that has 
opened the misc devices. Normally the vhost driver doesn't get notified when 
that happens.

> > +
> > +	/* RPMsg address of the position update endpoint */
> > +	u32 posn_addr;
> > +	/* position update buffer and work */
> > +	struct vhost_work posn_work;
> > +	struct sof_ipc_stream_posn posn;
> > +
> > +	/* IPC request buffer */
> > +	struct sof_rpmsg_ipc_req ipc_buf;
> > +	/* IPC response buffer */
> > +	u8 reply_buf[SOF_IPC_MSG_MAX_SIZE];
> > +	/*
> > +	 * data response header, captured audio data is copied directly from the
> > +	 * DMA buffer
> 
> so zero-copy is not supported for now, right?

Not yet, no, the infrastructure isn't in the mainline yet.

> > +	 */
> > +	struct sof_rpmsg_data_resp data_resp;
> > +};
> > +
> > +/* A guest is booting */
> > +static int vhost_dsp_activate(struct vhost_dsp *dsp)
> > +{
> > +	unsigned int i;
> > +	int ret = 0;
> > +
> > +	mutex_lock(&dsp->vrdev.dev.mutex);
> > +
> > +	/* Wait until all the VirtQueues have been initialised */
> > +	if (!dsp->active) {
> > +		struct vhost_virtqueue *vq;
> > +
> > +		for (i = 0, vq = dsp->vrdev.vq;
> > +		     i < ARRAY_SIZE(dsp->vrdev.vq);
> > +		     i++, vq++) {
> > +			/* .private_data is required != NULL */
> > +			vq->private_data = vq;
> > +			/* needed for re-initialisation upon guest reboot */
> > +			ret = vhost_vq_init_access(vq);
> > +			if (ret)
> > +				vq_err(vq,
> > +				       "%s(): error %d initialising vq #%d\n",
> > +				       __func__, ret, i);
> > +		}
> > +
> > +		/* Send an RPMsg namespace announcement */
> > +		if (!ret && !vhost_rpmsg_ns_announce(&dsp->vrdev, "sof_rpmsg",
> > +						     SOF_RPMSG_ADDR_IPC))
> > +			dsp->active = true;
> > +	}
> > +
> > +	mutex_unlock(&dsp->vrdev.dev.mutex);
> > +
> > +	return ret;
> > +}
> > +
> > +/* A guest is powered off or reset */
> > +static void vhost_dsp_deactivate(struct vhost_dsp *dsp)
> > +{
> > +	unsigned int i;
> > +
> > +	mutex_lock(&dsp->vrdev.dev.mutex);
> > +
> > +	if (dsp->active) {
> > +		struct vhost_virtqueue *vq;
> > +
> > +		dsp->active = false;
> 
> can you explain why this is not symmetrical with _activate above: there is
> no rmpsg communication here?

No, none is needed here. You only need to announce the name-space once when 
initialising, there's nothing to be done when cleaning up.

> > +
> > +		/* If a VM reboots sof_vhost_client_release() isn't called */
> > +		sof_vhost_topology_purge(dsp->snd);
> > +
> > +		/* signal, that we're inactive */
> > +		for (i = 0, vq = dsp->vrdev.vq;
> > +		     i < ARRAY_SIZE(dsp->vrdev.vq);
> > +		     i++, vq++) {
> > +			mutex_lock(&vq->mutex);
> > +			vq->private_data = NULL;
> > +			mutex_unlock(&vq->mutex);
> > +		}
> > +	}
> > +
> > +	mutex_unlock(&dsp->vrdev.dev.mutex);
> > +}
> > +
> 
> [...]
> 
> > +/* .ioctl(): we only use VHOST_SET_RUNNING in a non-default way */
> > +static long vhost_dsp_ioctl(struct file *filp, unsigned int ioctl,
> > +			    unsigned long arg)
> > +{
> > +	struct vhost_dsp *dsp = filp->private_data;
> > +	void __user *argp = (void __user *)arg;
> > +	struct vhost_adsp_topology tplg;
> > +	u64 __user *featurep = argp;
> > +	u64 features;
> > +	int start;
> > +	long ret;
> > +
> > +	switch (ioctl) {
> > +	case VHOST_GET_FEATURES:
> > +		features = VHOST_DSP_FEATURES;
> > +		if (copy_to_user(featurep, &features, sizeof(features)))
> > +			return -EFAULT;
> > +		return 0;
> > +	case VHOST_SET_FEATURES:
> > +		if (copy_from_user(&features, featurep, sizeof(features)))
> > +			return -EFAULT;
> > +		return vhost_dsp_set_features(dsp, features);
> > +	case VHOST_GET_BACKEND_FEATURES:
> > +		features = 0;
> > +		if (copy_to_user(featurep, &features, sizeof(features)))
> > +			return -EFAULT;
> > +		return 0;
> > +	case VHOST_SET_BACKEND_FEATURES:
> > +		if (copy_from_user(&features, featurep, sizeof(features)))
> > +			return -EFAULT;
> > +		if (features)
> > +			return -EOPNOTSUPP;
> > +		return 0;
> > +	case VHOST_RESET_OWNER:
> > +		mutex_lock(&dsp->vrdev.dev.mutex);
> > +		ret = vhost_dev_check_owner(&dsp->vrdev.dev);
> > +		if (!ret) {
> > +			struct vhost_umem *umem =
> > +				vhost_dev_reset_owner_prepare();
> > +			if (!umem) {
> > +				ret = -ENOMEM;
> > +			} else {
> > +				vhost_dev_stop(&dsp->vrdev.dev);
> > +				vhost_dev_reset_owner(&dsp->vrdev.dev, umem);
> > +			}
> > +		}
> > +		mutex_unlock(&dsp->vrdev.dev.mutex);
> > +		return ret;
> > +	case VHOST_SET_OWNER:
> > +		mutex_lock(&dsp->vrdev.dev.mutex);
> > +		ret = vhost_dev_set_owner(&dsp->vrdev.dev);
> > +		mutex_unlock(&dsp->vrdev.dev.mutex);
> > +		return ret;
> > +	case VHOST_SET_RUNNING:
> > +		if (copy_from_user(&start, argp, sizeof(start)))
> > +			return -EFAULT;
> > +
> > +		if (start)
> > +			return vhost_dsp_activate(dsp);
> > +
> > +		vhost_dsp_deactivate(dsp);
> > +		return 0;
> > +	case VHOST_ADSP_SET_GUEST_TPLG:
> > +		if (copy_from_user(&tplg, argp, sizeof(tplg)))
> > +			return -EFAULT;
> > +		return sof_vhost_set_tplg(dsp->snd, &tplg);
> > +	}
> 
> All cases seem to use return, so the the code below seems to be the default:
> case?

That's correct, it's the default / fall-back case.

> > +	mutex_lock(&dsp->vrdev.dev.mutex);
> > +	ret = vhost_dev_ioctl(&dsp->vrdev.dev, ioctl, argp);
> > +	if (ret == -ENOIOCTLCMD)
> > +		ret = vhost_vring_ioctl(&dsp->vrdev.dev, ioctl, argp);
> > +	mutex_unlock(&dsp->vrdev.dev.mutex);
> > +
> > +	return ret;
> > +}
> 
> [...]
> 
> > +static ssize_t vhost_dsp_ipc_write(struct vhost_rpmsg *vr,
> > +				   struct vhost_rpmsg_iter *iter)
> > +{
> > +	struct vhost_dsp *dsp = container_of(vr, struct vhost_dsp, vrdev);
> > +
> > +	return vhost_rpmsg_copy(vr, iter, dsp->reply_buf,
> > +				vhost_rpmsg_iter_len(iter)) ==
> > +		vhost_rpmsg_iter_len(iter) ? 0 : -EIO;
> > +}
> 
> This is rather convoluted code, with the same function called on both sides
> of a comparison.

It's a simple inline function, but sure, I can add a variable to cache its
result in it.

> > +
> > +/* Called only once to get guest's position update endpoint address */
> > +static ssize_t vhost_dsp_posn_read(struct vhost_rpmsg *vr,
> > +				   struct vhost_rpmsg_iter *iter)
> > +{
> > +	struct vhost_dsp *dsp = container_of(vr, struct vhost_dsp, vrdev);
> > +	struct vhost_virtqueue *vq = &dsp->vrdev.vq[VIRTIO_RPMSG_REQUEST];
> > +	size_t len = vhost_rpmsg_iter_len(iter);
> > +	size_t nbytes;
> > +
> > +	if ((int)dsp->posn_addr >= 0) {
> 
> posn_addr is defined as a u32, so what are you trying to test here?

It's initialised to -EINVAL, so, this tests, whether it has been set to a 
valid value since then. I can make the field s32 to make it clearer.

> > +		vq_err(vq, "%s(): position queue address %u already set\n",
> > +		       __func__, dsp->posn_addr);
> > +		return -EINVAL;
> > +	}
> > +
> > +	if (len != sizeof(dsp->posn_addr)) {
> 
> that also seems suspicious:
> 
> +	/* RPMsg address of the position update endpoint */
> +	u32 posn_addr;
> 
> why would a length which should have different values have anything to do
> with a constant 4 bytes?

We are dealing with user-space here, user-space data should be checked for 
validity.

> > +		vq_err(vq, "%s(): data count %zu invalid\n",
> > +		       __func__, len);
> > +		return -EINVAL;
> > +	}
> > +
> > +	nbytes = vhost_rpmsg_copy(vr, iter, &dsp->posn_addr,
> > +				  sizeof(dsp->posn_addr));
> > +	if (nbytes != sizeof(dsp->posn_addr)) {
> 
> and again here?

Copying can return 0 in case of a failure.

> > +		vq_err(vq,
> > +		       "%s(): got %zu instead of %zu bytes position update\n",
> > +		       __func__, nbytes, sizeof(dsp->posn_addr));
> > +		return -EIO;
> > +	}
> > +
> > +	pr_debug("%s(): guest position endpoint address 0x%x\n", __func__,
> > +		 dsp->posn_addr);
> > +
> > +	return 0;
> > +}
> > +
> 
> [...]
> 
> > +static int vhost_dsp_open(struct inode *inode, struct file *filp)
> > +{
> > +	struct miscdevice *misc = filp->private_data;
> > +	struct snd_sof_dev *sdev = dev_get_drvdata(misc->parent);
> > +	struct vhost_dsp *dsp = kmalloc(sizeof(*dsp), GFP_KERNEL);
> > +
> > +	if (!dsp)
> > +		return -ENOMEM;
> > +
> > +	dsp->vrdev.dev.mm = NULL;
> > +	dsp->snd = sof_vhost_client_add(sdev, dsp);
> > +	if (!dsp->snd) {
> > +		kfree(dsp);
> > +		return -ENOMEM;
> > +	}
> > +
> > +	/*
> > +	 * TODO: do we ever want to support multiple guest machines per DSP, if
> 
> That is a basic assumption yes.

Yes, that comment might need an update.

> > +	 * not, we might as well perform all allocations when registering the
> > +	 * misc device.
> > +	 */
> > +	dsp->active = false;
> > +	dsp->posn_addr = -EINVAL;
> > +	dsp->posn.rhdr.error = -ENODATA;
> > +
> > +	vhost_rpmsg_init(&dsp->vrdev, vhost_dsp_ept, ARRAY_SIZE(vhost_dsp_ept));
> > +	vhost_work_init(&dsp->posn_work, vhost_dsp_send_posn);
> > +
> > +	/* Overwrite file private data */
> > +	filp->private_data = dsp;
> > +
> > +	return 0;
> > +}
> 
> [...]
> 
> > +/* Always called from an interrupt thread context */
> > +static int vhost_dsp_update_posn(struct vhost_dsp *dsp,
> > +				 struct sof_ipc_stream_posn *posn)
> > +{
> > +	struct vhost_virtqueue *vq = &dsp->vrdev.vq[VIRTIO_RPMSG_RESPONSE];
> > +	int ret;
> > +
> > +	if (!dsp->active)
> > +		return 0;
> 
> is there a case where you can get a position update without the dsp being
> active?
> And shouldn't this be an error?

It isn't the DSP status, it's a guest status, so, yes, it's certainly 
possible, that a guest isn't active while position updates are coming for a 
different stream.

Thanks
Guennadi

> > +
> > +	memcpy(&dsp->posn, posn, sizeof(dsp->posn));
> > +
> > +	mutex_lock(&vq->mutex);
> > +
> > +	/*
> > +	 * VirtQueues can only be processed in the context of the VMM process or
> > +	 * a vhost work queue
> > +	 */
> > +	vhost_work_queue(&dsp->vrdev.dev, &dsp->posn_work);
> > +
> > +	mutex_unlock(&vq->mutex);
> > +
> > +	return ret;