// 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 {
                /* Here IRQs are assumed to be already disabled by the caller */
                spin_lock(&vioch->lock);
                list_add(&msg->list, &vioch->free_list);
                spin_unlock(&vioch->lock);
        }
}

static void scmi_vio_complete_cb(struct virtqueue *vqueue)
{
        unsigned long ready_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;
                }

                /* IRQs already disabled here no need to irqsave */
                spin_lock(&vioch->lock);
                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(&vioch->lock);

                if (msg) {
                        msg->rx_len = length;
                        scmi_rx_callback(vioch->cinfo,
                                         msg_read_header(msg->input), msg);

                        scmi_finalize_message(vioch, msg);
                }

                /*
                 * Release ready_lock and re-enable IRQs between loop iterations
                 * to allow virtio_chan_free() to possibly kick in and set the
                 * flag vioch->ready to false even in between processing of
                 * messages, so as to force outstanding messages to be ignored
                 * when system is shutting down.
                 */
                spin_unlock_irqrestore(&vioch->ready_lock, ready_flags);
        }

unlock_out:
        spin_unlock(&vioch->lock);
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;
}

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) {
                dev_err(dev,
                        "One SCMI Virtio device was already initialized: only one allowed.\n");
                return -EBUSY;
        }

        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;
        /* Ensure initialized scmi_vdev is visible */
        smp_store_mb(scmi_vdev, vdev);

        return 0;
}

static void scmi_vio_remove(struct virtio_device *vdev)
{
        /*
         * Once we get here, virtio_chan_free() will have already been called by
         * the SCMI core for any existing channel and, as a consequence, all the
         * virtio channels will have been already marked NOT ready, causing any
         * outstanding message on any vqueue to be ignored by complete_cb: now
         * we can just stop processing buffers and destroy the vqueues.
         */
        vdev->config->reset(vdev);
        vdev->config->del_vqs(vdev);
        /* Ensure scmi_vdev is visible as NULL */
        smp_store_mb(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 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,
};