--- /dev/null
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Virtio Transport driver for Arm System Control and Management Interface
+ * (SCMI).
+ *
+ * Copyright (C) 2020-2021 OpenSynergy.
+ * Copyright (C) 2021 ARM Ltd.
+ */
+
+/**
+ * DOC: Theory of Operation
+ *
+ * The scmi-virtio transport implements a driver for the virtio SCMI device.
+ *
+ * There is one Tx channel (virtio cmdq, A2P channel) and at most one Rx
+ * channel (virtio eventq, P2A channel). Each channel is implemented through a
+ * virtqueue. Access to each virtqueue is protected by spinlocks.
+ */
+
+#include <linux/errno.h>
+#include <linux/slab.h>
+#include <linux/virtio.h>
+#include <linux/virtio_config.h>
+
+#include <uapi/linux/virtio_ids.h>
+#include <uapi/linux/virtio_scmi.h>
+
+#include "common.h"
+
+#define VIRTIO_SCMI_MAX_MSG_SIZE 128 /* Value may be increased. */
+#define VIRTIO_SCMI_MAX_PDU_SIZE \
+ (VIRTIO_SCMI_MAX_MSG_SIZE + SCMI_MSG_MAX_PROT_OVERHEAD)
+#define DESCRIPTORS_PER_TX_MSG 2
+
+/**
+ * struct scmi_vio_channel - Transport channel information
+ *
+ * @vqueue: Associated virtqueue
+ * @cinfo: SCMI Tx or Rx channel
+ * @free_list: List of unused scmi_vio_msg, maintained for Tx channels only
+ * @is_rx: Whether channel is an Rx channel
+ * @ready: Whether transport user is ready to hear about channel
+ * @max_msg: Maximum number of pending messages for this channel.
+ * @lock: Protects access to all members except ready.
+ * @ready_lock: Protects access to ready. If required, it must be taken before
+ * lock.
+ */
+struct scmi_vio_channel {
+ struct virtqueue *vqueue;
+ struct scmi_chan_info *cinfo;
+ struct list_head free_list;
+ bool is_rx;
+ bool ready;
+ unsigned int max_msg;
+ /* lock to protect access to all members except ready. */
+ spinlock_t lock;
+ /* lock to rotects access to ready flag. */
+ spinlock_t ready_lock;
+};
+
+/**
+ * struct scmi_vio_msg - Transport PDU information
+ *
+ * @request: SDU used for commands
+ * @input: SDU used for (delayed) responses and notifications
+ * @list: List which scmi_vio_msg may be part of
+ * @rx_len: Input SDU size in bytes, once input has been received
+ */
+struct scmi_vio_msg {
+ struct scmi_msg_payld *request;
+ struct scmi_msg_payld *input;
+ struct list_head list;
+ unsigned int rx_len;
+};
+
+/* Only one SCMI VirtIO device can possibly exist */
+static struct virtio_device *scmi_vdev;
+
+static bool scmi_vio_have_vq_rx(struct virtio_device *vdev)
+{
+ return virtio_has_feature(vdev, VIRTIO_SCMI_F_P2A_CHANNELS);
+}
+
+static int scmi_vio_feed_vq_rx(struct scmi_vio_channel *vioch,
+ struct scmi_vio_msg *msg)
+{
+ struct scatterlist sg_in;
+ int rc;
+ unsigned long flags;
+
+ sg_init_one(&sg_in, msg->input, VIRTIO_SCMI_MAX_PDU_SIZE);
+
+ spin_lock_irqsave(&vioch->lock, flags);
+
+ rc = virtqueue_add_inbuf(vioch->vqueue, &sg_in, 1, msg, GFP_ATOMIC);
+ if (rc)
+ dev_err_once(vioch->cinfo->dev,
+ "failed to add to virtqueue (%d)\n", rc);
+ else
+ virtqueue_kick(vioch->vqueue);
+
+ spin_unlock_irqrestore(&vioch->lock, flags);
+
+ return rc;
+}
+
+static void scmi_finalize_message(struct scmi_vio_channel *vioch,
+ struct scmi_vio_msg *msg)
+{
+ if (vioch->is_rx) {
+ scmi_vio_feed_vq_rx(vioch, msg);
+ } else {
+ unsigned long flags;
+
+ spin_lock_irqsave(&vioch->lock, flags);
+ list_add(&msg->list, &vioch->free_list);
+ spin_unlock_irqrestore(&vioch->lock, flags);
+ }
+}
+
+static void scmi_vio_complete_cb(struct virtqueue *vqueue)
+{
+ unsigned long ready_flags;
+ unsigned long flags;
+ unsigned int length;
+ struct scmi_vio_channel *vioch;
+ struct scmi_vio_msg *msg;
+ bool cb_enabled = true;
+
+ if (WARN_ON_ONCE(!vqueue->vdev->priv))
+ return;
+ vioch = &((struct scmi_vio_channel *)vqueue->vdev->priv)[vqueue->index];
+
+ for (;;) {
+ spin_lock_irqsave(&vioch->ready_lock, ready_flags);
+
+ if (!vioch->ready) {
+ if (!cb_enabled)
+ (void)virtqueue_enable_cb(vqueue);
+ goto unlock_ready_out;
+ }
+
+ spin_lock_irqsave(&vioch->lock, flags);
+ if (cb_enabled) {
+ virtqueue_disable_cb(vqueue);
+ cb_enabled = false;
+ }
+ msg = virtqueue_get_buf(vqueue, &length);
+ if (!msg) {
+ if (virtqueue_enable_cb(vqueue))
+ goto unlock_out;
+ cb_enabled = true;
+ }
+ spin_unlock_irqrestore(&vioch->lock, flags);
+
+ if (msg) {
+ msg->rx_len = length;
+ scmi_rx_callback(vioch->cinfo,
+ msg_read_header(msg->input), msg);
+
+ scmi_finalize_message(vioch, msg);
+ }
+
+ spin_unlock_irqrestore(&vioch->ready_lock, ready_flags);
+ }
+
+unlock_out:
+ spin_unlock_irqrestore(&vioch->lock, flags);
+unlock_ready_out:
+ spin_unlock_irqrestore(&vioch->ready_lock, ready_flags);
+}
+
+static const char *const scmi_vio_vqueue_names[] = { "tx", "rx" };
+
+static vq_callback_t *scmi_vio_complete_callbacks[] = {
+ scmi_vio_complete_cb,
+ scmi_vio_complete_cb
+};
+
+static unsigned int virtio_get_max_msg(struct scmi_chan_info *base_cinfo)
+{
+ struct scmi_vio_channel *vioch = base_cinfo->transport_info;
+
+ return vioch->max_msg;
+}
+
+static int virtio_link_supplier(struct device *dev)
+{
+ if (!scmi_vdev) {
+ dev_notice_once(dev,
+ "Deferring probe after not finding a bound scmi-virtio device\n");
+ return -EPROBE_DEFER;
+ }
+
+ if (!device_link_add(dev, &scmi_vdev->dev,
+ DL_FLAG_AUTOREMOVE_CONSUMER)) {
+ dev_err(dev, "Adding link to supplier virtio device failed\n");
+ return -ECANCELED;
+ }
+
+ return 0;
+}
+
+static bool virtio_chan_available(struct device *dev, int idx)
+{
+ struct scmi_vio_channel *channels, *vioch = NULL;
+
+ if (WARN_ON_ONCE(!scmi_vdev))
+ return false;
+
+ channels = (struct scmi_vio_channel *)scmi_vdev->priv;
+
+ switch (idx) {
+ case VIRTIO_SCMI_VQ_TX:
+ vioch = &channels[VIRTIO_SCMI_VQ_TX];
+ break;
+ case VIRTIO_SCMI_VQ_RX:
+ if (scmi_vio_have_vq_rx(scmi_vdev))
+ vioch = &channels[VIRTIO_SCMI_VQ_RX];
+ break;
+ default:
+ return false;
+ }
+
+ return vioch && !vioch->cinfo ? true : false;
+}
+
+static int virtio_chan_setup(struct scmi_chan_info *cinfo, struct device *dev,
+ bool tx)
+{
+ unsigned long flags;
+ struct scmi_vio_channel *vioch;
+ int index = tx ? VIRTIO_SCMI_VQ_TX : VIRTIO_SCMI_VQ_RX;
+ int i;
+
+ if (!scmi_vdev)
+ return -EPROBE_DEFER;
+
+ vioch = &((struct scmi_vio_channel *)scmi_vdev->priv)[index];
+
+ for (i = 0; i < vioch->max_msg; i++) {
+ struct scmi_vio_msg *msg;
+
+ msg = devm_kzalloc(cinfo->dev, sizeof(*msg), GFP_KERNEL);
+ if (!msg)
+ return -ENOMEM;
+
+ if (tx) {
+ msg->request = devm_kzalloc(cinfo->dev,
+ VIRTIO_SCMI_MAX_PDU_SIZE,
+ GFP_KERNEL);
+ if (!msg->request)
+ return -ENOMEM;
+ }
+
+ msg->input = devm_kzalloc(cinfo->dev, VIRTIO_SCMI_MAX_PDU_SIZE,
+ GFP_KERNEL);
+ if (!msg->input)
+ return -ENOMEM;
+
+ if (tx) {
+ spin_lock_irqsave(&vioch->lock, flags);
+ list_add_tail(&msg->list, &vioch->free_list);
+ spin_unlock_irqrestore(&vioch->lock, flags);
+ } else {
+ scmi_vio_feed_vq_rx(vioch, msg);
+ }
+ }
+
+ spin_lock_irqsave(&vioch->lock, flags);
+ cinfo->transport_info = vioch;
+ /* Indirectly setting channel not available any more */
+ vioch->cinfo = cinfo;
+ spin_unlock_irqrestore(&vioch->lock, flags);
+
+ spin_lock_irqsave(&vioch->ready_lock, flags);
+ vioch->ready = true;
+ spin_unlock_irqrestore(&vioch->ready_lock, flags);
+
+ return 0;
+}
+
+static int virtio_chan_free(int id, void *p, void *data)
+{
+ unsigned long flags;
+ struct scmi_chan_info *cinfo = p;
+ struct scmi_vio_channel *vioch = cinfo->transport_info;
+
+ spin_lock_irqsave(&vioch->ready_lock, flags);
+ vioch->ready = false;
+ spin_unlock_irqrestore(&vioch->ready_lock, flags);
+
+ scmi_free_channel(cinfo, data, id);
+
+ spin_lock_irqsave(&vioch->lock, flags);
+ vioch->cinfo = NULL;
+ spin_unlock_irqrestore(&vioch->lock, flags);
+
+ return 0;
+}
+
+static int virtio_send_message(struct scmi_chan_info *cinfo,
+ struct scmi_xfer *xfer)
+{
+ struct scmi_vio_channel *vioch = cinfo->transport_info;
+ struct scatterlist sg_out;
+ struct scatterlist sg_in;
+ struct scatterlist *sgs[DESCRIPTORS_PER_TX_MSG] = { &sg_out, &sg_in };
+ unsigned long flags;
+ int rc;
+ struct scmi_vio_msg *msg;
+
+ spin_lock_irqsave(&vioch->lock, flags);
+
+ if (list_empty(&vioch->free_list)) {
+ spin_unlock_irqrestore(&vioch->lock, flags);
+ return -EBUSY;
+ }
+
+ msg = list_first_entry(&vioch->free_list, typeof(*msg), list);
+ list_del(&msg->list);
+
+ msg_tx_prepare(msg->request, xfer);
+
+ sg_init_one(&sg_out, msg->request, msg_command_size(xfer));
+ sg_init_one(&sg_in, msg->input, msg_response_size(xfer));
+
+ rc = virtqueue_add_sgs(vioch->vqueue, sgs, 1, 1, msg, GFP_ATOMIC);
+ if (rc) {
+ list_add(&msg->list, &vioch->free_list);
+ dev_err_once(vioch->cinfo->dev,
+ "%s() failed to add to virtqueue (%d)\n", __func__,
+ rc);
+ } else {
+ virtqueue_kick(vioch->vqueue);
+ }
+
+ spin_unlock_irqrestore(&vioch->lock, flags);
+
+ return rc;
+}
+
+static void virtio_fetch_response(struct scmi_chan_info *cinfo,
+ struct scmi_xfer *xfer)
+{
+ struct scmi_vio_msg *msg = xfer->priv;
+
+ if (msg) {
+ msg_fetch_response(msg->input, msg->rx_len, xfer);
+ xfer->priv = NULL;
+ }
+}
+
+static void virtio_fetch_notification(struct scmi_chan_info *cinfo,
+ size_t max_len, struct scmi_xfer *xfer)
+{
+ struct scmi_vio_msg *msg = xfer->priv;
+
+ if (msg) {
+ msg_fetch_notification(msg->input, msg->rx_len, max_len, xfer);
+ xfer->priv = NULL;
+ }
+}
+
+static const struct scmi_transport_ops scmi_virtio_ops = {
+ .link_supplier = virtio_link_supplier,
+ .chan_available = virtio_chan_available,
+ .chan_setup = virtio_chan_setup,
+ .chan_free = virtio_chan_free,
+ .get_max_msg = virtio_get_max_msg,
+ .send_message = virtio_send_message,
+ .fetch_response = virtio_fetch_response,
+ .fetch_notification = virtio_fetch_notification,
+};
+
+static int scmi_vio_probe(struct virtio_device *vdev)
+{
+ struct device *dev = &vdev->dev;
+ struct scmi_vio_channel *channels;
+ bool have_vq_rx;
+ int vq_cnt;
+ int i;
+ int ret;
+ struct virtqueue *vqs[VIRTIO_SCMI_VQ_MAX_CNT];
+
+ /* Only one SCMI VirtiO device allowed */
+ if (scmi_vdev)
+ return -EINVAL;
+
+ have_vq_rx = scmi_vio_have_vq_rx(vdev);
+ vq_cnt = have_vq_rx ? VIRTIO_SCMI_VQ_MAX_CNT : 1;
+
+ channels = devm_kcalloc(dev, vq_cnt, sizeof(*channels), GFP_KERNEL);
+ if (!channels)
+ return -ENOMEM;
+
+ if (have_vq_rx)
+ channels[VIRTIO_SCMI_VQ_RX].is_rx = true;
+
+ ret = virtio_find_vqs(vdev, vq_cnt, vqs, scmi_vio_complete_callbacks,
+ scmi_vio_vqueue_names, NULL);
+ if (ret) {
+ dev_err(dev, "Failed to get %d virtqueue(s)\n", vq_cnt);
+ return ret;
+ }
+
+ for (i = 0; i < vq_cnt; i++) {
+ unsigned int sz;
+
+ spin_lock_init(&channels[i].lock);
+ spin_lock_init(&channels[i].ready_lock);
+ INIT_LIST_HEAD(&channels[i].free_list);
+ channels[i].vqueue = vqs[i];
+
+ sz = virtqueue_get_vring_size(channels[i].vqueue);
+ /* Tx messages need multiple descriptors. */
+ if (!channels[i].is_rx)
+ sz /= DESCRIPTORS_PER_TX_MSG;
+
+ if (sz > MSG_TOKEN_MAX) {
+ dev_info_once(dev,
+ "%s virtqueue could hold %d messages. Only %ld allowed to be pending.\n",
+ channels[i].is_rx ? "rx" : "tx",
+ sz, MSG_TOKEN_MAX);
+ sz = MSG_TOKEN_MAX;
+ }
+ channels[i].max_msg = sz;
+ }
+
+ vdev->priv = channels;
+ scmi_vdev = vdev;
+
+ return 0;
+}
+
+static void scmi_vio_remove(struct virtio_device *vdev)
+{
+ vdev->config->reset(vdev);
+ vdev->config->del_vqs(vdev);
+ scmi_vdev = NULL;
+}
+
+static int scmi_vio_validate(struct virtio_device *vdev)
+{
+ if (!virtio_has_feature(vdev, VIRTIO_F_VERSION_1)) {
+ dev_err(&vdev->dev,
+ "device does not comply with spec version 1.x\n");
+ return -EINVAL;
+ }
+
+ return 0;
+}
+
+static unsigned int features[] = {
+ VIRTIO_SCMI_F_P2A_CHANNELS,
+};
+
+static const struct virtio_device_id id_table[] = {
+ { VIRTIO_ID_SCMI, VIRTIO_DEV_ANY_ID },
+ { 0 }
+};
+
+static struct virtio_driver virtio_scmi_driver = {
+ .driver.name = "scmi-virtio",
+ .driver.owner = THIS_MODULE,
+ .feature_table = features,
+ .feature_table_size = ARRAY_SIZE(features),
+ .id_table = id_table,
+ .probe = scmi_vio_probe,
+ .remove = scmi_vio_remove,
+ .validate = scmi_vio_validate,
+};
+
+static int __init virtio_scmi_init(void)
+{
+ return register_virtio_driver(&virtio_scmi_driver);
+}
+
+static void __exit virtio_scmi_exit(void)
+{
+ unregister_virtio_driver(&virtio_scmi_driver);
+}
+
+const struct scmi_desc scmi_virtio_desc = {
+ .transport_init = virtio_scmi_init,
+ .transport_exit = virtio_scmi_exit,
+ .ops = &scmi_virtio_ops,
+ .max_rx_timeout_ms = 60000, /* for non-realtime virtio devices */
+ .max_msg = 0, /* overridden by virtio_get_max_msg() */
+ .max_msg_size = VIRTIO_SCMI_MAX_MSG_SIZE,
+};
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