/*
   *  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
  ", 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
  ", 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
  ", 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_status(bus->ec, msg);
  	if (result < 0) {
  		dev_err(dev, "Error transferring EC i2c message %d
  ", 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
  ", 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
  ");
  		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
  ");
  		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
  ");
  		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");