ALSA: virtio: handling control messages

The control queue can be used by different parts of the driver to send
commands to the device. Control messages can be either synchronous or
asynchronous. The lifetime of a message is controlled by a reference
count.

Introduce a module parameter to set the message completion timeout:
  msg_timeout_ms [=1000]
Signed-off-by: Anton Yakovlev <anton.yakovlev@opensynergy.com>
Link: https://lore.kernel.org/r/20210302164709.3142702-4-anton.yakovlev@opensynergy.comSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/virtio/Makefile

@@ -3,5 +3,6 @@
 obj-$(CONFIG_SND_VIRTIO) += virtio_snd.o
 
 virtio_snd-objs := \
-	virtio_card.o
+	virtio_card.o \
+	virtio_ctl_msg.o
 

sound/virtio/virtio_card.c

@@ -11,6 +11,10 @@
 
 #include "virtio_card.h"
 
+u32 virtsnd_msg_timeout_ms = MSEC_PER_SEC;
+module_param_named(msg_timeout_ms, virtsnd_msg_timeout_ms, uint, 0644);
+MODULE_PARM_DESC(msg_timeout_ms, "Message completion timeout in milliseconds");
+
 static void virtsnd_remove(struct virtio_device *vdev);
 
 /**
@@ -96,9 +100,11 @@ static int virtsnd_find_vqs(struct virtio_snd *snd)
 {
 	struct virtio_device *vdev = snd->vdev;
 	static vq_callback_t *callbacks[VIRTIO_SND_VQ_MAX] = {
+		[VIRTIO_SND_VQ_CONTROL] = virtsnd_ctl_notify_cb,
 		[VIRTIO_SND_VQ_EVENT] = virtsnd_event_notify_cb
 	};
 	static const char *names[VIRTIO_SND_VQ_MAX] = {
+		[VIRTIO_SND_VQ_CONTROL] = "virtsnd-ctl",
 		[VIRTIO_SND_VQ_EVENT] = "virtsnd-event"
 	};
 	struct virtqueue *vqs[VIRTIO_SND_VQ_MAX] = { 0 };
@@ -226,6 +232,11 @@ static int virtsnd_validate(struct virtio_device *vdev)
 		return -EINVAL;
 	}
 
+	if (!virtsnd_msg_timeout_ms) {
+		dev_err(&vdev->dev, "msg_timeout_ms value cannot be zero\n");
+		return -EINVAL;
+	}
+
 	return 0;
 }
 
@@ -247,6 +258,7 @@ static int virtsnd_probe(struct virtio_device *vdev)
 		return -ENOMEM;
 
 	snd->vdev = vdev;
+	INIT_LIST_HEAD(&snd->ctl_msgs);
 
 	vdev->priv = snd;
 
@@ -283,6 +295,7 @@ static void virtsnd_remove(struct virtio_device *vdev)
 	struct virtio_snd *snd = vdev->priv;
 
 	virtsnd_disable_event_vq(snd);
+	virtsnd_ctl_msg_cancel_all(snd);
 
 	if (snd->card)
 		snd_card_free(snd->card);

sound/virtio/virtio_card.h

@@ -11,6 +11,8 @@
 #include <sound/core.h>
 #include <uapi/linux/virtio_snd.h>
 
+#include "virtio_ctl_msg.h"
+
 #define VIRTIO_SND_CARD_DRIVER	"virtio-snd"
 #define VIRTIO_SND_CARD_NAME	"VirtIO SoundCard"
 
@@ -29,15 +31,20 @@ struct virtio_snd_queue {
  * @vdev: Underlying virtio device.
  * @queues: Virtqueue wrappers.
  * @card: ALSA sound card.
+ * @ctl_msgs: Pending control request list.
  * @event_msgs: Device events.
  */
 struct virtio_snd {
 	struct virtio_device *vdev;
 	struct virtio_snd_queue queues[VIRTIO_SND_VQ_MAX];
 	struct snd_card *card;
+	struct list_head ctl_msgs;
 	struct virtio_snd_event *event_msgs;
 };
 
+/* Message completion timeout in milliseconds (module parameter). */
+extern u32 virtsnd_msg_timeout_ms;
+
 static inline struct virtio_snd_queue *
 virtsnd_control_queue(struct virtio_snd *snd)
 {

sound/virtio/virtio_ctl_msg.c

+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * virtio-snd: Virtio sound device
+ * Copyright (C) 2021 OpenSynergy GmbH
+ */
+#include <linux/moduleparam.h>
+#include <linux/virtio_config.h>
+
+#include "virtio_card.h"
+
+/**
+ * struct virtio_snd_msg - Control message.
+ * @sg_request: Scattergather list containing a device request (header).
+ * @sg_response: Scattergather list containing a device response (status).
+ * @list: Pending message list entry.
+ * @notify: Request completed notification.
+ * @ref_count: Reference count used to manage a message lifetime.
+ */
+struct virtio_snd_msg {
+	struct scatterlist sg_request;
+	struct scatterlist sg_response;
+	struct list_head list;
+	struct completion notify;
+	refcount_t ref_count;
+};
+
+/**
+ * virtsnd_ctl_msg_ref() - Increment reference counter for the message.
+ * @msg: Control message.
+ *
+ * Context: Any context.
+ */
+void virtsnd_ctl_msg_ref(struct virtio_snd_msg *msg)
+{
+	refcount_inc(&msg->ref_count);
+}
+
+/**
+ * virtsnd_ctl_msg_unref() - Decrement reference counter for the message.
+ * @msg: Control message.
+ *
+ * The message will be freed when the ref_count value is 0.
+ *
+ * Context: Any context.
+ */
+void virtsnd_ctl_msg_unref(struct virtio_snd_msg *msg)
+{
+	if (refcount_dec_and_test(&msg->ref_count))
+		kfree(msg);
+}
+
+/**
+ * virtsnd_ctl_msg_request() - Get a pointer to the request header.
+ * @msg: Control message.
+ *
+ * Context: Any context.
+ */
+void *virtsnd_ctl_msg_request(struct virtio_snd_msg *msg)
+{
+	return sg_virt(&msg->sg_request);
+}
+
+/**
+ * virtsnd_ctl_msg_request() - Get a pointer to the response header.
+ * @msg: Control message.
+ *
+ * Context: Any context.
+ */
+void *virtsnd_ctl_msg_response(struct virtio_snd_msg *msg)
+{
+	return sg_virt(&msg->sg_response);
+}
+
+/**
+ * virtsnd_ctl_msg_alloc() - Allocate and initialize a control message.
+ * @request_size: Size of request header.
+ * @response_size: Size of response header.
+ * @gfp: Kernel flags for memory allocation.
+ *
+ * The message will be automatically freed when the ref_count value is 0.
+ *
+ * Context: Any context. May sleep if @gfp flags permit.
+ * Return: Allocated message on success, NULL on failure.
+ */
+struct virtio_snd_msg *virtsnd_ctl_msg_alloc(size_t request_size,
+					     size_t response_size, gfp_t gfp)
+{
+	struct virtio_snd_msg *msg;
+
+	if (!request_size || !response_size)
+		return NULL;
+
+	msg = kzalloc(sizeof(*msg) + request_size + response_size, gfp);
+	if (!msg)
+		return NULL;
+
+	sg_init_one(&msg->sg_request, (u8 *)msg + sizeof(*msg), request_size);
+	sg_init_one(&msg->sg_response, (u8 *)msg + sizeof(*msg) + request_size,
+		    response_size);
+
+	INIT_LIST_HEAD(&msg->list);
+	init_completion(&msg->notify);
+	/* This reference is dropped in virtsnd_ctl_msg_complete(). */
+	refcount_set(&msg->ref_count, 1);
+
+	return msg;
+}
+
+/**
+ * virtsnd_ctl_msg_send() - Send a control message.
+ * @snd: VirtIO sound device.
+ * @msg: Control message.
+ * @out_sgs: Additional sg-list to attach to the request header (may be NULL).
+ * @in_sgs: Additional sg-list to attach to the response header (may be NULL).
+ * @nowait: Flag indicating whether to wait for completion.
+ *
+ * Context: Any context. Takes and releases the control queue spinlock.
+ *          May sleep if @nowait is false.
+ * Return: 0 on success, -errno on failure.
+ */
+int virtsnd_ctl_msg_send(struct virtio_snd *snd, struct virtio_snd_msg *msg,
+			 struct scatterlist *out_sgs,
+			 struct scatterlist *in_sgs, bool nowait)
+{
+	struct virtio_device *vdev = snd->vdev;
+	struct virtio_snd_queue *queue = virtsnd_control_queue(snd);
+	unsigned int js = msecs_to_jiffies(virtsnd_msg_timeout_ms);
+	struct virtio_snd_hdr *request = virtsnd_ctl_msg_request(msg);
+	struct virtio_snd_hdr *response = virtsnd_ctl_msg_response(msg);
+	unsigned int nouts = 0;
+	unsigned int nins = 0;
+	struct scatterlist *psgs[4];
+	bool notify = false;
+	unsigned long flags;
+	int rc;
+
+	virtsnd_ctl_msg_ref(msg);
+
+	/* Set the default status in case the message was canceled. */
+	response->code = cpu_to_le32(VIRTIO_SND_S_IO_ERR);
+
+	psgs[nouts++] = &msg->sg_request;
+	if (out_sgs)
+		psgs[nouts++] = out_sgs;
+
+	psgs[nouts + nins++] = &msg->sg_response;
+	if (in_sgs)
+		psgs[nouts + nins++] = in_sgs;
+
+	spin_lock_irqsave(&queue->lock, flags);
+	rc = virtqueue_add_sgs(queue->vqueue, psgs, nouts, nins, msg,
+			       GFP_ATOMIC);
+	if (!rc) {
+		notify = virtqueue_kick_prepare(queue->vqueue);
+
+		list_add_tail(&msg->list, &snd->ctl_msgs);
+	}
+	spin_unlock_irqrestore(&queue->lock, flags);
+
+	if (rc) {
+		dev_err(&vdev->dev, "failed to send control message (0x%08x)\n",
+			le32_to_cpu(request->code));
+
+		/*
+		 * Since in this case virtsnd_ctl_msg_complete() will not be
+		 * called, it is necessary to decrement the reference count.
+		 */
+		virtsnd_ctl_msg_unref(msg);
+
+		goto on_exit;
+	}
+
+	if (notify)
+		virtqueue_notify(queue->vqueue);
+
+	if (nowait)
+		goto on_exit;
+
+	rc = wait_for_completion_interruptible_timeout(&msg->notify, js);
+	if (rc <= 0) {
+		if (!rc) {
+			dev_err(&vdev->dev,
+				"control message (0x%08x) timeout\n",
+				le32_to_cpu(request->code));
+			rc = -ETIMEDOUT;
+		}
+
+		goto on_exit;
+	}
+
+	switch (le32_to_cpu(response->code)) {
+	case VIRTIO_SND_S_OK:
+		rc = 0;
+		break;
+	case VIRTIO_SND_S_NOT_SUPP:
+		rc = -EOPNOTSUPP;
+		break;
+	case VIRTIO_SND_S_IO_ERR:
+		rc = -EIO;
+		break;
+	default:
+		rc = -EINVAL;
+		break;
+	}
+
+on_exit:
+	virtsnd_ctl_msg_unref(msg);
+
+	return rc;
+}
+
+/**
+ * virtsnd_ctl_msg_complete() - Complete a control message.
+ * @msg: Control message.
+ *
+ * Context: Any context. Expects the control queue spinlock to be held by
+ *          caller.
+ */
+void virtsnd_ctl_msg_complete(struct virtio_snd_msg *msg)
+{
+	list_del(&msg->list);
+	complete(&msg->notify);
+
+	virtsnd_ctl_msg_unref(msg);
+}
+
+/**
+ * virtsnd_ctl_msg_cancel_all() - Cancel all pending control messages.
+ * @snd: VirtIO sound device.
+ *
+ * Context: Any context.
+ */
+void virtsnd_ctl_msg_cancel_all(struct virtio_snd *snd)
+{
+	struct virtio_snd_queue *queue = virtsnd_control_queue(snd);
+	unsigned long flags;
+
+	spin_lock_irqsave(&queue->lock, flags);
+	while (!list_empty(&snd->ctl_msgs)) {
+		struct virtio_snd_msg *msg =
+			list_first_entry(&snd->ctl_msgs, struct virtio_snd_msg,
+					 list);
+
+		virtsnd_ctl_msg_complete(msg);
+	}
+	spin_unlock_irqrestore(&queue->lock, flags);
+}
+
+/**
+ * virtsnd_ctl_query_info() - Query the item configuration from the device.
+ * @snd: VirtIO sound device.
+ * @command: Control request code (VIRTIO_SND_R_XXX_INFO).
+ * @start_id: Item start identifier.
+ * @count: Item count to query.
+ * @size: Item information size in bytes.
+ * @info: Buffer for storing item information.
+ *
+ * Context: Any context that permits to sleep.
+ * Return: 0 on success, -errno on failure.
+ */
+int virtsnd_ctl_query_info(struct virtio_snd *snd, int command, int start_id,
+			   int count, size_t size, void *info)
+{
+	struct virtio_snd_msg *msg;
+	struct virtio_snd_query_info *query;
+	struct scatterlist sg;
+
+	msg = virtsnd_ctl_msg_alloc(sizeof(*query),
+				    sizeof(struct virtio_snd_hdr), GFP_KERNEL);
+	if (!msg)
+		return -ENOMEM;
+
+	query = virtsnd_ctl_msg_request(msg);
+	query->hdr.code = cpu_to_le32(command);
+	query->start_id = cpu_to_le32(start_id);
+	query->count = cpu_to_le32(count);
+	query->size = cpu_to_le32(size);
+
+	sg_init_one(&sg, info, count * size);
+
+	return virtsnd_ctl_msg_send(snd, msg, NULL, &sg, false);
+}
+
+/**
+ * virtsnd_ctl_notify_cb() - Process all completed control messages.
+ * @vqueue: Underlying control virtqueue.
+ *
+ * This callback function is called upon a vring interrupt request from the
+ * device.
+ *
+ * Context: Interrupt context. Takes and releases the control queue spinlock.
+ */
+void virtsnd_ctl_notify_cb(struct virtqueue *vqueue)
+{
+	struct virtio_snd *snd = vqueue->vdev->priv;
+	struct virtio_snd_queue *queue = virtsnd_control_queue(snd);
+	struct virtio_snd_msg *msg;
+	u32 length;
+	unsigned long flags;
+
+	spin_lock_irqsave(&queue->lock, flags);
+	do {
+		virtqueue_disable_cb(vqueue);
+		while ((msg = virtqueue_get_buf(vqueue, &length)))
+			virtsnd_ctl_msg_complete(msg);
+		if (unlikely(virtqueue_is_broken(vqueue)))
+			break;
+	} while (!virtqueue_enable_cb(vqueue));
+	spin_unlock_irqrestore(&queue->lock, flags);
+}

sound/virtio/virtio_ctl_msg.h

+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * virtio-snd: Virtio sound device
+ * Copyright (C) 2021 OpenSynergy GmbH
+ */
+#ifndef VIRTIO_SND_MSG_H
+#define VIRTIO_SND_MSG_H
+
+#include <linux/atomic.h>
+#include <linux/virtio.h>
+
+struct virtio_snd;
+struct virtio_snd_msg;
+
+void virtsnd_ctl_msg_ref(struct virtio_snd_msg *msg);
+
+void virtsnd_ctl_msg_unref(struct virtio_snd_msg *msg);
+
+void *virtsnd_ctl_msg_request(struct virtio_snd_msg *msg);
+
+void *virtsnd_ctl_msg_response(struct virtio_snd_msg *msg);
+
+struct virtio_snd_msg *virtsnd_ctl_msg_alloc(size_t request_size,
+					     size_t response_size, gfp_t gfp);
+
+int virtsnd_ctl_msg_send(struct virtio_snd *snd, struct virtio_snd_msg *msg,
+			 struct scatterlist *out_sgs,
+			 struct scatterlist *in_sgs, bool nowait);
+
+/**
+ * virtsnd_ctl_msg_send_sync() - Simplified sending of synchronous message.
+ * @snd: VirtIO sound device.
+ * @msg: Control message.
+ *
+ * After returning from this function, the message will be deleted. If message
+ * content is still needed, the caller must additionally to
+ * virtsnd_ctl_msg_ref/unref() it.
+ *
+ * The msg_timeout_ms module parameter defines the message completion timeout.
+ * If the message is not completed within this time, the function will return an
+ * error.
+ *
+ * Context: Any context that permits to sleep.
+ * Return: 0 on success, -errno on failure.
+ *
+ * The return value is a message status code (VIRTIO_SND_S_XXX) converted to an
+ * appropriate -errno value.
+ */
+static inline int virtsnd_ctl_msg_send_sync(struct virtio_snd *snd,
+					    struct virtio_snd_msg *msg)
+{
+	return virtsnd_ctl_msg_send(snd, msg, NULL, NULL, false);
+}
+
+/**
+ * virtsnd_ctl_msg_send_async() - Simplified sending of asynchronous message.
+ * @snd: VirtIO sound device.
+ * @msg: Control message.
+ *
+ * Context: Any context.
+ * Return: 0 on success, -errno on failure.
+ */
+static inline int virtsnd_ctl_msg_send_async(struct virtio_snd *snd,
+					     struct virtio_snd_msg *msg)
+{
+	return virtsnd_ctl_msg_send(snd, msg, NULL, NULL, true);
+}
+
+void virtsnd_ctl_msg_cancel_all(struct virtio_snd *snd);
+
+void virtsnd_ctl_msg_complete(struct virtio_snd_msg *msg);
+
+int virtsnd_ctl_query_info(struct virtio_snd *snd, int command, int start_id,
+			   int count, size_t size, void *info);
+
+void virtsnd_ctl_notify_cb(struct virtqueue *vqueue);
+
+#endif /* VIRTIO_SND_MSG_H */