/*
 *  Copyright (C) 2013 Google, Inc
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 * Expose an I2C passthrough to the ChromeOS EC.
 */

#include <linux/module.h>
#include <linux/i2c.h>
#include <linux/mfd/cros_ec.h>
#include <linux/mfd/cros_ec_commands.h>
#include <linux/platform_device.h>
#include <linux/slab.h>

#define I2C_MAX_RETRIES 3

/**
 * struct ec_i2c_device - Driver data for I2C tunnel
 *
 * @dev: Device node
 * @adap: I2C adapter
 * @ec: Pointer to EC device
 * @remote_bus: The EC bus number we tunnel to on the other side.
 * @request_buf: Buffer for transmitting data; we expect most transfers to fit.
 * @response_buf: Buffer for receiving data; we expect most transfers to fit.
 */

struct ec_i2c_device {
        struct device *dev;
        struct i2c_adapter adap;
        struct cros_ec_device *ec;

        u16 remote_bus;

        u8 request_buf[256];
        u8 response_buf[256];
};

/**
 * ec_i2c_count_message - Count bytes needed for ec_i2c_construct_message
 *
 * @i2c_msgs: The i2c messages to read
 * @num: The number of i2c messages.
 *
 * Returns the number of bytes the messages will take up.
 */
static int ec_i2c_count_message(const struct i2c_msg i2c_msgs[], int num)
{
        int i;
        int size;

        size = sizeof(struct ec_params_i2c_passthru);
        size += num * sizeof(struct ec_params_i2c_passthru_msg);
        for (i = 0; i < num; i++)
                if (!(i2c_msgs[i].flags & I2C_M_RD))
                        size += i2c_msgs[i].len;

        return size;
}

/**
 * ec_i2c_construct_message - construct a message to go to the EC
 *
 * This function effectively stuffs the standard i2c_msg format of Linux into
 * a format that the EC understands.
 *
 * @buf: The buffer to fill.  We assume that the buffer is big enough.
 * @i2c_msgs: The i2c messages to read.
 * @num: The number of i2c messages.
 * @bus_num: The remote bus number we want to talk to.
 *
 * Returns 0 or a negative error number.
 */
static int ec_i2c_construct_message(u8 *buf, const struct i2c_msg i2c_msgs[],
                                    int num, u16 bus_num)
{
        struct ec_params_i2c_passthru *params;
        u8 *out_data;
        int i;

        out_data = buf + sizeof(struct ec_params_i2c_passthru) +
                   num * sizeof(struct ec_params_i2c_passthru_msg);

        params = (struct ec_params_i2c_passthru *)buf;
        params->port = bus_num;
        params->num_msgs = num;
        for (i = 0; i < num; i++) {
                const struct i2c_msg *i2c_msg = &i2c_msgs[i];
                struct ec_params_i2c_passthru_msg *msg = &params->msg[i];

                msg->len = i2c_msg->len;
                msg->addr_flags = i2c_msg->addr;

                if (i2c_msg->flags & I2C_M_TEN)
                        return -EINVAL;

                if (i2c_msg->flags & I2C_M_RD) {
                        msg->addr_flags |= EC_I2C_FLAG_READ;
                } else {
                        memcpy(out_data, i2c_msg->buf, msg->len);
                        out_data += msg->len;
                }
        }

        return 0;
}

/**
 * ec_i2c_count_response - Count bytes needed for ec_i2c_parse_response
 *
 * @i2c_msgs: The i2c messages to to fill up.
 * @num: The number of i2c messages expected.
 *
 * Returns the number of response bytes expeced.
 */
static int ec_i2c_count_response(struct i2c_msg i2c_msgs[], int num)
{
        int size;
        int i;

        size = sizeof(struct ec_response_i2c_passthru);
        for (i = 0; i < num; i++)
                if (i2c_msgs[i].flags & I2C_M_RD)
                        size += i2c_msgs[i].len;

        return size;
}

/**
 * ec_i2c_parse_response - Parse a response from the EC
 *
 * We'll take the EC's response and copy it back into msgs.
 *
 * @buf: The buffer to parse.
 * @i2c_msgs: The i2c messages to to fill up.
 * @num: The number of i2c messages; will be modified to include the actual
 *       number received.
 *
 * Returns 0 or a negative error number.
 */
static int ec_i2c_parse_response(const u8 *buf, struct i2c_msg i2c_msgs[],
                                 int *num)
{
        const struct ec_response_i2c_passthru *resp;
        const u8 *in_data;
        int i;

        in_data = buf + sizeof(struct ec_response_i2c_passthru);

        resp = (const struct ec_response_i2c_passthru *)buf;
        if (resp->i2c_status & EC_I2C_STATUS_TIMEOUT)
                return -ETIMEDOUT;
        else if (resp->i2c_status & EC_I2C_STATUS_ERROR)
                return -EREMOTEIO;

        /* Other side could send us back fewer messages, but not more */
        if (resp->num_msgs > *num)
                return -EPROTO;
        *num = resp->num_msgs;

        for (i = 0; i < *num; i++) {
                struct i2c_msg *i2c_msg = &i2c_msgs[i];

                if (i2c_msgs[i].flags & I2C_M_RD) {
                        memcpy(i2c_msg->buf, in_data, i2c_msg->len);
                        in_data += i2c_msg->len;
                }
        }

        return 0;
}

static int ec_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg i2c_msgs[],
                       int num)
{
        struct ec_i2c_device *bus = adap->algo_data;
        struct device *dev = bus->dev;
        const u16 bus_num = bus->remote_bus;
        int request_len;
        int response_len;
        int alloc_size;
        int result;
        struct cros_ec_command *msg;

        request_len = ec_i2c_count_message(i2c_msgs, num);
        if (request_len < 0) {
                dev_warn(dev, "Error constructing message %d\n", request_len);
                return request_len;
        }

        response_len = ec_i2c_count_response(i2c_msgs, num);
        if (response_len < 0) {
                /* Unexpected; no errors should come when NULL response */
                dev_warn(dev, "Error preparing response %d\n", response_len);
                return response_len;
        }

        alloc_size = max(request_len, response_len);
        msg = kmalloc(sizeof(*msg) + alloc_size, GFP_KERNEL);
        if (!msg)
                return -ENOMEM;

        result = ec_i2c_construct_message(msg->data, i2c_msgs, num, bus_num);
        if (result) {
                dev_err(dev, "Error constructing EC i2c message %d\n", result);
                goto exit;
        }

        msg->version = 0;
        msg->command = EC_CMD_I2C_PASSTHRU;
        msg->outsize = request_len;
        msg->insize = response_len;

        result = cros_ec_cmd_xfer(bus->ec, msg);
        if (result < 0) {
                dev_err(dev, "Error transferring EC i2c message %d\n", result);
                goto exit;
        }

        result = ec_i2c_parse_response(msg->data, i2c_msgs, &num);
        if (result < 0) {
                dev_err(dev, "Error parsing EC i2c message %d\n", result);
                goto exit;
        }

        /* Indicate success by saying how many messages were sent */
        result = num;
exit:
        kfree(msg);
        return result;
}

static u32 ec_i2c_functionality(struct i2c_adapter *adap)
{
        return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL;
}

static const struct i2c_algorithm ec_i2c_algorithm = {
        .master_xfer    = ec_i2c_xfer,
        .functionality  = ec_i2c_functionality,
};

static int ec_i2c_probe(struct platform_device *pdev)
{
        struct device_node *np = pdev->dev.of_node;
        struct cros_ec_device *ec = dev_get_drvdata(pdev->dev.parent);
        struct device *dev = &pdev->dev;
        struct ec_i2c_device *bus = NULL;
        u32 remote_bus;
        int err;

        if (!ec->cmd_xfer) {
                dev_err(dev, "Missing sendrecv\n");
                return -EINVAL;
        }

        bus = devm_kzalloc(dev, sizeof(*bus), GFP_KERNEL);
        if (bus == NULL)
                return -ENOMEM;

        err = of_property_read_u32(np, "google,remote-bus", &remote_bus);
        if (err) {
                dev_err(dev, "Couldn't read remote-bus property\n");
                return err;
        }
        bus->remote_bus = remote_bus;

        bus->ec = ec;
        bus->dev = dev;

        bus->adap.owner = THIS_MODULE;
        strlcpy(bus->adap.name, "cros-ec-i2c-tunnel", sizeof(bus->adap.name));
        bus->adap.algo = &ec_i2c_algorithm;
        bus->adap.algo_data = bus;
        bus->adap.dev.parent = &pdev->dev;
        bus->adap.dev.of_node = np;
        bus->adap.retries = I2C_MAX_RETRIES;

        err = i2c_add_adapter(&bus->adap);
        if (err) {
                dev_err(dev, "cannot register i2c adapter\n");
                return err;
        }
        platform_set_drvdata(pdev, bus);

        return err;
}

static int ec_i2c_remove(struct platform_device *dev)
{
        struct ec_i2c_device *bus = platform_get_drvdata(dev);

        i2c_del_adapter(&bus->adap);

        return 0;
}

#ifdef CONFIG_OF
static const struct of_device_id cros_ec_i2c_of_match[] = {
        { .compatible = "google,cros-ec-i2c-tunnel" },
        {},
};
MODULE_DEVICE_TABLE(of, cros_ec_i2c_of_match);
#endif

static struct platform_driver ec_i2c_tunnel_driver = {
        .probe = ec_i2c_probe,
        .remove = ec_i2c_remove,
        .driver = {
                .name = "cros-ec-i2c-tunnel",
                .of_match_table = of_match_ptr(cros_ec_i2c_of_match),
        },
};

module_platform_driver(ec_i2c_tunnel_driver);

MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("EC I2C tunnel driver");
MODULE_ALIAS("platform:cros-ec-i2c-tunnel");