// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Virtio I2C Bus Driver
 *
 * The Virtio I2C Specification:
 * https://raw.githubusercontent.com/oasis-tcs/virtio-spec/master/virtio-i2c.tex
 *
 * Copyright (c) 2021 Intel Corporation. All rights reserved.
 */

#include <linux/acpi.h>
#include <linux/completion.h>
#include <linux/err.h>
#include <linux/i2c.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/virtio.h>
#include <linux/virtio_ids.h>
#include <linux/virtio_config.h>
#include <linux/virtio_i2c.h>

/**
 * struct virtio_i2c - virtio I2C data
 * @vdev: virtio device for this controller
 * @adap: I2C adapter for this controller
 * @vq: the virtio virtqueue for communication
 */
struct virtio_i2c {
        struct virtio_device *vdev;
        struct i2c_adapter adap;
        struct virtqueue *vq;
};

/**
 * struct virtio_i2c_req - the virtio I2C request structure
 * @completion: completion of virtio I2C message
 * @out_hdr: the OUT header of the virtio I2C message
 * @buf: the buffer into which data is read, or from which it's written
 * @in_hdr: the IN header of the virtio I2C message
 */
struct virtio_i2c_req {
        struct completion completion;
        struct virtio_i2c_out_hdr out_hdr       ____cacheline_aligned;
        uint8_t *buf                            ____cacheline_aligned;
        struct virtio_i2c_in_hdr in_hdr         ____cacheline_aligned;
};

static void virtio_i2c_msg_done(struct virtqueue *vq)
{
        struct virtio_i2c_req *req;
        unsigned int len;

        while ((req = virtqueue_get_buf(vq, &len)))
                complete(&req->completion);
}

static int virtio_i2c_prepare_reqs(struct virtqueue *vq,
                                   struct virtio_i2c_req *reqs,
                                   struct i2c_msg *msgs, int num)
{
        struct scatterlist *sgs[3], out_hdr, msg_buf, in_hdr;
        int i;

        for (i = 0; i < num; i++) {
                int outcnt = 0, incnt = 0;

                init_completion(&reqs[i].completion);

                /*
                 * Only 7-bit mode supported for this moment. For the address
                 * format, Please check the Virtio I2C Specification.
                 */
                reqs[i].out_hdr.addr = cpu_to_le16(msgs[i].addr << 1);

                if (msgs[i].flags & I2C_M_RD)
                        reqs[i].out_hdr.flags |= cpu_to_le32(VIRTIO_I2C_FLAGS_M_RD);

                if (i != num - 1)
                        reqs[i].out_hdr.flags |= cpu_to_le32(VIRTIO_I2C_FLAGS_FAIL_NEXT);

                sg_init_one(&out_hdr, &reqs[i].out_hdr, sizeof(reqs[i].out_hdr));
                sgs[outcnt++] = &out_hdr;

                if (msgs[i].len) {
                        reqs[i].buf = i2c_get_dma_safe_msg_buf(&msgs[i], 1);
                        if (!reqs[i].buf)
                                break;

                        sg_init_one(&msg_buf, reqs[i].buf, msgs[i].len);

                        if (msgs[i].flags & I2C_M_RD)
                                sgs[outcnt + incnt++] = &msg_buf;
                        else
                                sgs[outcnt++] = &msg_buf;
                }

                sg_init_one(&in_hdr, &reqs[i].in_hdr, sizeof(reqs[i].in_hdr));
                sgs[outcnt + incnt++] = &in_hdr;

                if (virtqueue_add_sgs(vq, sgs, outcnt, incnt, &reqs[i], GFP_KERNEL)) {
                        i2c_put_dma_safe_msg_buf(reqs[i].buf, &msgs[i], false);
                        break;
                }
        }

        return i;
}

static int virtio_i2c_complete_reqs(struct virtqueue *vq,
                                    struct virtio_i2c_req *reqs,
                                    struct i2c_msg *msgs, int num)
{
        bool failed = false;
        int i, j = 0;

        for (i = 0; i < num; i++) {
                struct virtio_i2c_req *req = &reqs[i];

                if (!failed) {
                        if (wait_for_completion_interruptible(&req->completion))
                                failed = true;
                        else if (req->in_hdr.status != VIRTIO_I2C_MSG_OK)
                                failed = true;
                        else
                                j++;
                }

                i2c_put_dma_safe_msg_buf(reqs[i].buf, &msgs[i], !failed);
        }

        return j;
}

static int virtio_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs,
                           int num)
{
        struct virtio_i2c *vi = i2c_get_adapdata(adap);
        struct virtqueue *vq = vi->vq;
        struct virtio_i2c_req *reqs;
        int count;

        reqs = kzalloc_objs(*reqs, num);
        if (!reqs)
                return -ENOMEM;

        count = virtio_i2c_prepare_reqs(vq, reqs, msgs, num);
        if (!count)
                goto err_free;

        /*
         * For the case where count < num, i.e. we weren't able to queue all the
         * msgs, ideally we should abort right away and return early, but some
         * of the messages are already sent to the remote I2C controller and the
         * virtqueue will be left in undefined state in that case. We kick the
         * remote here to clear the virtqueue, so we can try another set of
         * messages later on.
         */
        virtqueue_kick(vq);

        count = virtio_i2c_complete_reqs(vq, reqs, msgs, count);

err_free:
        kfree(reqs);
        return count;
}

static void virtio_i2c_del_vqs(struct virtio_device *vdev)
{
        virtio_reset_device(vdev);
        vdev->config->del_vqs(vdev);
}

static int virtio_i2c_setup_vqs(struct virtio_i2c *vi)
{
        struct virtio_device *vdev = vi->vdev;

        vi->vq = virtio_find_single_vq(vdev, virtio_i2c_msg_done, "msg");
        return PTR_ERR_OR_ZERO(vi->vq);
}

static u32 virtio_i2c_func(struct i2c_adapter *adap)
{
        return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL;
}

static const struct i2c_algorithm virtio_algorithm = {
        .xfer = virtio_i2c_xfer,
        .functionality = virtio_i2c_func,
};

static int virtio_i2c_probe(struct virtio_device *vdev)
{
        struct virtio_i2c *vi;
        int ret;

        if (!virtio_has_feature(vdev, VIRTIO_I2C_F_ZERO_LENGTH_REQUEST))
                return dev_err_probe(&vdev->dev, -EINVAL,
                                     "Zero-length request feature is mandatory\n");

        vi = devm_kzalloc(&vdev->dev, sizeof(*vi), GFP_KERNEL);
        if (!vi)
                return -ENOMEM;

        vdev->priv = vi;
        vi->vdev = vdev;

        ret = virtio_i2c_setup_vqs(vi);
        if (ret)
                return ret;

        vi->adap.owner = THIS_MODULE;
        snprintf(vi->adap.name, sizeof(vi->adap.name),
                 "i2c_virtio at virtio bus %d", vdev->index);
        vi->adap.algo = &virtio_algorithm;
        vi->adap.dev.parent = &vdev->dev;
        vi->adap.dev.of_node = vdev->dev.of_node;
        i2c_set_adapdata(&vi->adap, vi);

        /*
         * Setup ACPI node for controlled devices which will be probed through
         * ACPI.
         */
        ACPI_COMPANION_SET(&vi->adap.dev, ACPI_COMPANION(vdev->dev.parent));

        ret = i2c_add_adapter(&vi->adap);
        if (ret)
                virtio_i2c_del_vqs(vdev);

        return ret;
}

static void virtio_i2c_remove(struct virtio_device *vdev)
{
        struct virtio_i2c *vi = vdev->priv;

        i2c_del_adapter(&vi->adap);
        virtio_i2c_del_vqs(vdev);
}

static const struct virtio_device_id id_table[] = {
        { VIRTIO_ID_I2C_ADAPTER, VIRTIO_DEV_ANY_ID },
        {}
};
MODULE_DEVICE_TABLE(virtio, id_table);

static int virtio_i2c_freeze(struct virtio_device *vdev)
{
        virtio_i2c_del_vqs(vdev);
        return 0;
}

static int virtio_i2c_restore(struct virtio_device *vdev)
{
        return virtio_i2c_setup_vqs(vdev->priv);
}

static const unsigned int features[] = {
        VIRTIO_I2C_F_ZERO_LENGTH_REQUEST,
};

static struct virtio_driver virtio_i2c_driver = {
        .feature_table          = features,
        .feature_table_size     = ARRAY_SIZE(features),
        .id_table               = id_table,
        .probe                  = virtio_i2c_probe,
        .remove                 = virtio_i2c_remove,
        .driver                 = {
                .name   = "i2c_virtio",
        },
        .freeze                 = pm_sleep_ptr(virtio_i2c_freeze),
        .restore                = pm_sleep_ptr(virtio_i2c_restore),
};
module_virtio_driver(virtio_i2c_driver);

MODULE_AUTHOR("Jie Deng <jie.deng@intel.com>");
MODULE_AUTHOR("Conghui Chen <conghui.chen@intel.com>");
MODULE_DESCRIPTION("Virtio i2c bus driver");
MODULE_LICENSE("GPL");