/*
   * BCM2835 master mode driver
   *
   * This software is licensed under the terms of the GNU General Public
   * License version 2, as published by the Free Software Foundation, and
   * may be copied, distributed, and modified under those terms.
   *
   * This program is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   * GNU General Public License for more details.
   */
  
  #include <linux/clk.h>
  #include <linux/completion.h>
  #include <linux/err.h>
  #include <linux/i2c.h>
  #include <linux/interrupt.h>
  #include <linux/io.h>
  #include <linux/module.h>
  #include <linux/platform_device.h>
  #include <linux/slab.h>
  
  #define BCM2835_I2C_C		0x0
  #define BCM2835_I2C_S		0x4
  #define BCM2835_I2C_DLEN	0x8
  #define BCM2835_I2C_A		0xc
  #define BCM2835_I2C_FIFO	0x10
  #define BCM2835_I2C_DIV		0x14
  #define BCM2835_I2C_DEL		0x18
  #define BCM2835_I2C_CLKT	0x1c
  
  #define BCM2835_I2C_C_READ	BIT(0)
  #define BCM2835_I2C_C_CLEAR	BIT(4) /* bits 4 and 5 both clear */
  #define BCM2835_I2C_C_ST	BIT(7)
  #define BCM2835_I2C_C_INTD	BIT(8)
  #define BCM2835_I2C_C_INTT	BIT(9)
  #define BCM2835_I2C_C_INTR	BIT(10)
  #define BCM2835_I2C_C_I2CEN	BIT(15)
  
  #define BCM2835_I2C_S_TA	BIT(0)
  #define BCM2835_I2C_S_DONE	BIT(1)
  #define BCM2835_I2C_S_TXW	BIT(2)
  #define BCM2835_I2C_S_RXR	BIT(3)
  #define BCM2835_I2C_S_TXD	BIT(4)
  #define BCM2835_I2C_S_RXD	BIT(5)
  #define BCM2835_I2C_S_TXE	BIT(6)
  #define BCM2835_I2C_S_RXF	BIT(7)
  #define BCM2835_I2C_S_ERR	BIT(8)
  #define BCM2835_I2C_S_CLKT	BIT(9)
  #define BCM2835_I2C_S_LEN	BIT(10) /* Fake bit for SW error reporting */
  
  #define BCM2835_I2C_BITMSK_S	0x03FF
  
  #define BCM2835_I2C_CDIV_MIN	0x0002
  #define BCM2835_I2C_CDIV_MAX	0xFFFE
  
  #define BCM2835_I2C_TIMEOUT (msecs_to_jiffies(1000))
  
  struct bcm2835_i2c_dev {
  	struct device *dev;
  	void __iomem *regs;
  	struct clk *clk;
  	int irq;
  	struct i2c_adapter adapter;
  	struct completion completion;
  	u32 msg_err;
  	u8 *msg_buf;
  	size_t msg_buf_remaining;
  };
  
  static inline void bcm2835_i2c_writel(struct bcm2835_i2c_dev *i2c_dev,
  				      u32 reg, u32 val)
  {
  	writel(val, i2c_dev->regs + reg);
  }
  
  static inline u32 bcm2835_i2c_readl(struct bcm2835_i2c_dev *i2c_dev, u32 reg)
  {
  	return readl(i2c_dev->regs + reg);
  }
  
  static void bcm2835_fill_txfifo(struct bcm2835_i2c_dev *i2c_dev)
  {
  	u32 val;
  
  	while (i2c_dev->msg_buf_remaining) {
  		val = bcm2835_i2c_readl(i2c_dev, BCM2835_I2C_S);
  		if (!(val & BCM2835_I2C_S_TXD))
  			break;
  		bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_FIFO,
  				   *i2c_dev->msg_buf);
  		i2c_dev->msg_buf++;
  		i2c_dev->msg_buf_remaining--;
  	}
  }
  
  static void bcm2835_drain_rxfifo(struct bcm2835_i2c_dev *i2c_dev)
  {
  	u32 val;
  
  	while (i2c_dev->msg_buf_remaining) {
  		val = bcm2835_i2c_readl(i2c_dev, BCM2835_I2C_S);
  		if (!(val & BCM2835_I2C_S_RXD))
  			break;
  		*i2c_dev->msg_buf = bcm2835_i2c_readl(i2c_dev,
  						      BCM2835_I2C_FIFO);
  		i2c_dev->msg_buf++;
  		i2c_dev->msg_buf_remaining--;
  	}
  }
  
  static irqreturn_t bcm2835_i2c_isr(int this_irq, void *data)
  {
  	struct bcm2835_i2c_dev *i2c_dev = data;
  	u32 val, err;
  
  	val = bcm2835_i2c_readl(i2c_dev, BCM2835_I2C_S);
  	val &= BCM2835_I2C_BITMSK_S;
  	bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_S, val);
  
  	err = val & (BCM2835_I2C_S_CLKT | BCM2835_I2C_S_ERR);
  	if (err) {
  		i2c_dev->msg_err = err;
  		complete(&i2c_dev->completion);
  		return IRQ_HANDLED;
  	}
  
  	if (val & BCM2835_I2C_S_RXD) {
  		bcm2835_drain_rxfifo(i2c_dev);
  		if (!(val & BCM2835_I2C_S_DONE))
  			return IRQ_HANDLED;
  	}
  
  	if (val & BCM2835_I2C_S_DONE) {
  		if (i2c_dev->msg_buf_remaining)
  			i2c_dev->msg_err = BCM2835_I2C_S_LEN;
  		else
  			i2c_dev->msg_err = 0;
  		complete(&i2c_dev->completion);
  		return IRQ_HANDLED;
  	}
  
  	if (val & BCM2835_I2C_S_TXD) {
  		bcm2835_fill_txfifo(i2c_dev);
  		return IRQ_HANDLED;
  	}
  
  	return IRQ_NONE;
  }
  
  static int bcm2835_i2c_xfer_msg(struct bcm2835_i2c_dev *i2c_dev,
  				struct i2c_msg *msg)
  {
  	u32 c;
  	unsigned long time_left;
  
  	i2c_dev->msg_buf = msg->buf;
  	i2c_dev->msg_buf_remaining = msg->len;
  	reinit_completion(&i2c_dev->completion);
  
  	bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_C, BCM2835_I2C_C_CLEAR);
  
  	if (msg->flags & I2C_M_RD) {
  		c = BCM2835_I2C_C_READ | BCM2835_I2C_C_INTR;
  	} else {
  		c = BCM2835_I2C_C_INTT;
  		bcm2835_fill_txfifo(i2c_dev);
  	}
  	c |= BCM2835_I2C_C_ST | BCM2835_I2C_C_INTD | BCM2835_I2C_C_I2CEN;
  
  	bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_A, msg->addr);
  	bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_DLEN, msg->len);
  	bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_C, c);
  
  	time_left = wait_for_completion_timeout(&i2c_dev->completion,
  						BCM2835_I2C_TIMEOUT);
  	bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_C, BCM2835_I2C_C_CLEAR);
  	if (!time_left) {
  		dev_err(i2c_dev->dev, "i2c transfer timed out
  ");
  		return -ETIMEDOUT;
  	}
  
  	if (likely(!i2c_dev->msg_err))
  		return 0;
  
  	if ((i2c_dev->msg_err & BCM2835_I2C_S_ERR) &&
  	    (msg->flags & I2C_M_IGNORE_NAK))
  		return 0;
  
  	dev_err(i2c_dev->dev, "i2c transfer failed: %x
  ", i2c_dev->msg_err);
  
  	if (i2c_dev->msg_err & BCM2835_I2C_S_ERR)
  		return -EREMOTEIO;
  	else
  		return -EIO;
  }
  
  static int bcm2835_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg msgs[],
  			    int num)
  {
  	struct bcm2835_i2c_dev *i2c_dev = i2c_get_adapdata(adap);
  	int i;
  	int ret = 0;
  
  	for (i = 0; i < num; i++) {
  		ret = bcm2835_i2c_xfer_msg(i2c_dev, &msgs[i]);
  		if (ret)
  			break;
  	}
  
  	return ret ?: i;
  }
  
  static u32 bcm2835_i2c_func(struct i2c_adapter *adap)
  {
  	return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL;
  }
  
  static const struct i2c_algorithm bcm2835_i2c_algo = {
  	.master_xfer	= bcm2835_i2c_xfer,
  	.functionality	= bcm2835_i2c_func,
  };
  
  static int bcm2835_i2c_probe(struct platform_device *pdev)
  {
  	struct bcm2835_i2c_dev *i2c_dev;
  	struct resource *mem, *irq;
  	u32 bus_clk_rate, divider;
  	int ret;
  	struct i2c_adapter *adap;
  
  	i2c_dev = devm_kzalloc(&pdev->dev, sizeof(*i2c_dev), GFP_KERNEL);
  	if (!i2c_dev)
  		return -ENOMEM;
  	platform_set_drvdata(pdev, i2c_dev);
  	i2c_dev->dev = &pdev->dev;
  	init_completion(&i2c_dev->completion);
  
  	mem = platform_get_resource(pdev, IORESOURCE_MEM, 0);
  	i2c_dev->regs = devm_ioremap_resource(&pdev->dev, mem);
  	if (IS_ERR(i2c_dev->regs))
  		return PTR_ERR(i2c_dev->regs);
  
  	i2c_dev->clk = devm_clk_get(&pdev->dev, NULL);
  	if (IS_ERR(i2c_dev->clk)) {
  		dev_err(&pdev->dev, "Could not get clock
  ");
  		return PTR_ERR(i2c_dev->clk);
  	}
  
  	ret = of_property_read_u32(pdev->dev.of_node, "clock-frequency",
  				   &bus_clk_rate);
  	if (ret < 0) {
  		dev_warn(&pdev->dev,
  			 "Could not read clock-frequency property
  ");
  		bus_clk_rate = 100000;
  	}
  
  	divider = DIV_ROUND_UP(clk_get_rate(i2c_dev->clk), bus_clk_rate);
  	/*
  	 * Per the datasheet, the register is always interpreted as an even
  	 * number, by rounding down. In other words, the LSB is ignored. So,
  	 * if the LSB is set, increment the divider to avoid any issue.
  	 */
  	if (divider & 1)
  		divider++;
  	if ((divider < BCM2835_I2C_CDIV_MIN) ||
  	    (divider > BCM2835_I2C_CDIV_MAX)) {
  		dev_err(&pdev->dev, "Invalid clock-frequency
  ");
  		return -ENODEV;
  	}
  	bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_DIV, divider);
  
  	irq = platform_get_resource(pdev, IORESOURCE_IRQ, 0);
  	if (!irq) {
  		dev_err(&pdev->dev, "No IRQ resource
  ");
  		return -ENODEV;
  	}
  	i2c_dev->irq = irq->start;
  
  	ret = request_irq(i2c_dev->irq, bcm2835_i2c_isr, IRQF_SHARED,
  			  dev_name(&pdev->dev), i2c_dev);
  	if (ret) {
  		dev_err(&pdev->dev, "Could not request IRQ
  ");
  		return -ENODEV;
  	}
  
  	adap = &i2c_dev->adapter;
  	i2c_set_adapdata(adap, i2c_dev);
  	adap->owner = THIS_MODULE;
  	adap->class = I2C_CLASS_DEPRECATED;
  	strlcpy(adap->name, "bcm2835 I2C adapter", sizeof(adap->name));
  	adap->algo = &bcm2835_i2c_algo;
  	adap->dev.parent = &pdev->dev;
  	adap->dev.of_node = pdev->dev.of_node;
  
  	bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_C, 0);
  
  	ret = i2c_add_adapter(adap);
  	if (ret)
  		free_irq(i2c_dev->irq, i2c_dev);
  
  	return ret;
  }
  
  static int bcm2835_i2c_remove(struct platform_device *pdev)
  {
  	struct bcm2835_i2c_dev *i2c_dev = platform_get_drvdata(pdev);
  
  	free_irq(i2c_dev->irq, i2c_dev);
  	i2c_del_adapter(&i2c_dev->adapter);
  
  	return 0;
  }
  
  static const struct of_device_id bcm2835_i2c_of_match[] = {
  	{ .compatible = "brcm,bcm2835-i2c" },
  	{},
  };
  MODULE_DEVICE_TABLE(of, bcm2835_i2c_of_match);
  
  static struct platform_driver bcm2835_i2c_driver = {
  	.probe		= bcm2835_i2c_probe,
  	.remove		= bcm2835_i2c_remove,
  	.driver		= {
  		.name	= "i2c-bcm2835",
  		.of_match_table = bcm2835_i2c_of_match,
  	},
  };
  module_platform_driver(bcm2835_i2c_driver);
  
  MODULE_AUTHOR("Stephen Warren <swarren@wwwdotorg.org>");
  MODULE_DESCRIPTION("BCM2835 I2C bus adapter");
  MODULE_LICENSE("GPL v2");
  MODULE_ALIAS("platform:i2c-bcm2835");