drivers/i2c/busses/i2c-bcm2835.c - linux - Git at Google

 /*
  * 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_FEDL_SHIFT	16
 #define BCM2835_I2C_REDL_SHIFT	0

 #define BCM2835_I2C_CDIV_MIN	0x0002
 #define BCM2835_I2C_CDIV_MAX	0xFFFE

 struct bcm2835_i2c_dev {
 	struct device *dev;
 	void __iomem *regs;
 	struct clk *clk;
 	int irq;
 	u32 bus_clk_rate;
 	struct i2c_adapter adapter;
 	struct completion completion;
 	struct i2c_msg *curr_msg;
 	int num_msgs;
 	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 int bcm2835_i2c_set_divider(struct bcm2835_i2c_dev *i2c_dev)
 {
 	u32 divider, redl, fedl;

 	divider = DIV_ROUND_UP(clk_get_rate(i2c_dev->clk),
 			       i2c_dev->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_ratelimited(i2c_dev->dev, "Invalid clock-frequency\n");
 		return -EINVAL;
 	}

 	bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_DIV, divider);

 	/*
 	 * Number of core clocks to wait after falling edge before
 	 * outputting the next data bit.  Note that both FEDL and REDL
 	 * can't be greater than CDIV/2.
 	 */
 	fedl = max(divider / 16, 1u);

 	/*
 	 * Number of core clocks to wait after rising edge before
 	 * sampling the next incoming data bit.
 	 */
 	redl = max(divider / 4, 1u);

 	bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_DEL,
 			   (fedl << BCM2835_I2C_FEDL_SHIFT) |
 			   (redl << BCM2835_I2C_REDL_SHIFT));
 	return 0;
 }

 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--;
 	}
 }

 /*
  * Repeated Start Condition (Sr)
  * The BCM2835 ARM Peripherals datasheet mentions a way to trigger a Sr when it
  * talks about reading from a slave with 10 bit address. This is achieved by
  * issuing a write, poll the I2CS.TA flag and wait for it to be set, and then
  * issue a read.
  * A comment in https://github.com/raspberrypi/linux/issues/254 shows how the
  * firmware actually does it using polling and says that it's a workaround for
  * a problem in the state machine.
  * It turns out that it is possible to use the TXW interrupt to know when the
  * transfer is active, provided the FIFO has not been prefilled.
  */

 static void bcm2835_i2c_start_transfer(struct bcm2835_i2c_dev *i2c_dev)
 {
 	u32 c = BCM2835_I2C_C_ST | BCM2835_I2C_C_I2CEN;
 	struct i2c_msg *msg = i2c_dev->curr_msg;
 	bool last_msg = (i2c_dev->num_msgs == 1);

 	if (!i2c_dev->num_msgs)
 		return;

 	i2c_dev->num_msgs--;
 	i2c_dev->msg_buf = msg->buf;
 	i2c_dev->msg_buf_remaining = msg->len;

 	if (msg->flags & I2C_M_RD)
 		c |= BCM2835_I2C_C_READ | BCM2835_I2C_C_INTR;
 	else
 		c |= BCM2835_I2C_C_INTT;

 	if (last_msg)
 		c |= BCM2835_I2C_C_INTD;

 	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);
 }

 /*
  * Note about I2C_C_CLEAR on error:
  * The I2C_C_CLEAR on errors will take some time to resolve -- if you were in
  * non-idle state and I2C_C_READ, it sets an abort_rx flag and runs through
  * the state machine to send a NACK and a STOP. Since we're setting CLEAR
  * without I2CEN, that NACK will be hanging around queued up for next time
  * we start the engine.
  */

 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);

 	err = val & (BCM2835_I2C_S_CLKT | BCM2835_I2C_S_ERR);
 	if (err) {
 		i2c_dev->msg_err = err;
 		goto complete;
 	}

 	if (val & BCM2835_I2C_S_DONE) {
 		if (!i2c_dev->curr_msg) {
 			dev_err(i2c_dev->dev, "Got unexpected interrupt (from firmware?)\n");
 		} else if (i2c_dev->curr_msg->flags & I2C_M_RD) {
 			bcm2835_drain_rxfifo(i2c_dev);
 			val = bcm2835_i2c_readl(i2c_dev, BCM2835_I2C_S);
 		}

 		if ((val & BCM2835_I2C_S_RXD) || i2c_dev->msg_buf_remaining)
 			i2c_dev->msg_err = BCM2835_I2C_S_LEN;
 		else
 			i2c_dev->msg_err = 0;
 		goto complete;
 	}

 	if (val & BCM2835_I2C_S_TXW) {
 		if (!i2c_dev->msg_buf_remaining) {
 			i2c_dev->msg_err = val | BCM2835_I2C_S_LEN;
 			goto complete;
 		}

 		bcm2835_fill_txfifo(i2c_dev);

 		if (i2c_dev->num_msgs && !i2c_dev->msg_buf_remaining) {
 			i2c_dev->curr_msg++;
 			bcm2835_i2c_start_transfer(i2c_dev);
 		}

 		return IRQ_HANDLED;
 	}

 	if (val & BCM2835_I2C_S_RXR) {
 		if (!i2c_dev->msg_buf_remaining) {
 			i2c_dev->msg_err = val | BCM2835_I2C_S_LEN;
 			goto complete;
 		}

 		bcm2835_drain_rxfifo(i2c_dev);
 		return IRQ_HANDLED;
 	}

 	return IRQ_NONE;

 complete:
 	bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_C, BCM2835_I2C_C_CLEAR);
 	bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_S, BCM2835_I2C_S_CLKT |
 			   BCM2835_I2C_S_ERR | BCM2835_I2C_S_DONE);
 	complete(&i2c_dev->completion);

 	return IRQ_HANDLED;
 }

 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);
 	unsigned long time_left;
 	int i, ret;

 	for (i = 0; i < (num - 1); i++)
 		if (msgs[i].flags & I2C_M_RD) {
 			dev_warn_once(i2c_dev->dev,
 				      "only one read message supported, has to be last\n");
 			return -EOPNOTSUPP;
 		}

 	ret = bcm2835_i2c_set_divider(i2c_dev);
 	if (ret)
 		return ret;

 	i2c_dev->curr_msg = msgs;
 	i2c_dev->num_msgs = num;
 	reinit_completion(&i2c_dev->completion);

 	bcm2835_i2c_start_transfer(i2c_dev);

 	time_left = wait_for_completion_timeout(&i2c_dev->completion,
 						adap->timeout);
 	if (!time_left) {
 		bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_C,
 				   BCM2835_I2C_C_CLEAR);
 		dev_err(i2c_dev->dev, "i2c transfer timed out\n");
 		return -ETIMEDOUT;
 	}

 	if (!i2c_dev->msg_err)
 		return num;

 	dev_dbg(i2c_dev->dev, "i2c transfer failed: %x\n", i2c_dev->msg_err);

 	if (i2c_dev->msg_err & BCM2835_I2C_S_ERR)
 		return -EREMOTEIO;

 	return -EIO;
 }

 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,
 };

 /*
  * This HW was reported to have problems with clock stretching:
  * http://www.advamation.com/knowhow/raspberrypi/rpi-i2c-bug.html
  * https://www.raspberrypi.org/forums/viewtopic.php?p=146272
  */
 static const struct i2c_adapter_quirks bcm2835_i2c_quirks = {
 	.flags = I2C_AQ_NO_CLK_STRETCH,
 };

 static int bcm2835_i2c_probe(struct platform_device *pdev)
 {
 	struct bcm2835_i2c_dev *i2c_dev;
 	struct resource *mem, *irq;
 	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)) {
 		if (PTR_ERR(i2c_dev->clk) != -EPROBE_DEFER)
 			dev_err(&pdev->dev, "Could not get clock\n");
 		return PTR_ERR(i2c_dev->clk);
 	}

 	ret = of_property_read_u32(pdev->dev.of_node, "clock-frequency",
 				   &i2c_dev->bus_clk_rate);
 	if (ret < 0) {
 		dev_warn(&pdev->dev,
 			 "Could not read clock-frequency property\n");
 		i2c_dev->bus_clk_rate = 100000;
 	}

 	irq = platform_get_resource(pdev, IORESOURCE_IRQ, 0);
 	if (!irq) {
 		dev_err(&pdev->dev, "No IRQ resource\n");
 		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\n");
 		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;
 	adap->quirks = &bcm2835_i2c_quirks;

 	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");
	/*
	* 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_FEDL_SHIFT 16
	#define BCM2835_I2C_REDL_SHIFT 0

	#define BCM2835_I2C_CDIV_MIN 0x0002
	#define BCM2835_I2C_CDIV_MAX 0xFFFE

	struct bcm2835_i2c_dev {
	struct device *dev;
	void __iomem *regs;
	struct clk *clk;
	int irq;
	u32 bus_clk_rate;
	struct i2c_adapter adapter;
	struct completion completion;
	struct i2c_msg *curr_msg;
	int num_msgs;
	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 int bcm2835_i2c_set_divider(struct bcm2835_i2c_dev *i2c_dev)
	{
	u32 divider, redl, fedl;

	divider = DIV_ROUND_UP(clk_get_rate(i2c_dev->clk),
	i2c_dev->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_ratelimited(i2c_dev->dev, "Invalid clock-frequency\n");
	return -EINVAL;
	}

	bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_DIV, divider);

	/*
	* Number of core clocks to wait after falling edge before
	* outputting the next data bit. Note that both FEDL and REDL
	* can't be greater than CDIV/2.
	*/
	fedl = max(divider / 16, 1u);

	/*
	* Number of core clocks to wait after rising edge before
	* sampling the next incoming data bit.
	*/
	redl = max(divider / 4, 1u);

	bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_DEL,
	(fedl << BCM2835_I2C_FEDL_SHIFT) \|
	(redl << BCM2835_I2C_REDL_SHIFT));
	return 0;
	}

	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--;
	}
	}

	/*
	* Repeated Start Condition (Sr)
	* The BCM2835 ARM Peripherals datasheet mentions a way to trigger a Sr when it
	* talks about reading from a slave with 10 bit address. This is achieved by
	* issuing a write, poll the I2CS.TA flag and wait for it to be set, and then
	* issue a read.
	* A comment in https://github.com/raspberrypi/linux/issues/254 shows how the
	* firmware actually does it using polling and says that it's a workaround for
	* a problem in the state machine.
	* It turns out that it is possible to use the TXW interrupt to know when the
	* transfer is active, provided the FIFO has not been prefilled.
	*/

	static void bcm2835_i2c_start_transfer(struct bcm2835_i2c_dev *i2c_dev)
	{
	u32 c = BCM2835_I2C_C_ST \| BCM2835_I2C_C_I2CEN;
	struct i2c_msg *msg = i2c_dev->curr_msg;
	bool last_msg = (i2c_dev->num_msgs == 1);

	if (!i2c_dev->num_msgs)
	return;

	i2c_dev->num_msgs--;
	i2c_dev->msg_buf = msg->buf;
	i2c_dev->msg_buf_remaining = msg->len;

	if (msg->flags & I2C_M_RD)
	c \|= BCM2835_I2C_C_READ \| BCM2835_I2C_C_INTR;
	else
	c \|= BCM2835_I2C_C_INTT;

	if (last_msg)
	c \|= BCM2835_I2C_C_INTD;

	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);
	}

	/*
	* Note about I2C_C_CLEAR on error:
	* The I2C_C_CLEAR on errors will take some time to resolve -- if you were in
	* non-idle state and I2C_C_READ, it sets an abort_rx flag and runs through
	* the state machine to send a NACK and a STOP. Since we're setting CLEAR
	* without I2CEN, that NACK will be hanging around queued up for next time
	* we start the engine.
	*/

	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);

	err = val & (BCM2835_I2C_S_CLKT \| BCM2835_I2C_S_ERR);
	if (err) {
	i2c_dev->msg_err = err;
	goto complete;
	}

	if (val & BCM2835_I2C_S_DONE) {
	if (!i2c_dev->curr_msg) {
	dev_err(i2c_dev->dev, "Got unexpected interrupt (from firmware?)\n");
	} else if (i2c_dev->curr_msg->flags & I2C_M_RD) {
	bcm2835_drain_rxfifo(i2c_dev);
	val = bcm2835_i2c_readl(i2c_dev, BCM2835_I2C_S);
	}

	if ((val & BCM2835_I2C_S_RXD) \|\| i2c_dev->msg_buf_remaining)
	i2c_dev->msg_err = BCM2835_I2C_S_LEN;
	else
	i2c_dev->msg_err = 0;
	goto complete;
	}

	if (val & BCM2835_I2C_S_TXW) {
	if (!i2c_dev->msg_buf_remaining) {
	i2c_dev->msg_err = val \| BCM2835_I2C_S_LEN;
	goto complete;
	}

	bcm2835_fill_txfifo(i2c_dev);

	if (i2c_dev->num_msgs && !i2c_dev->msg_buf_remaining) {
	i2c_dev->curr_msg++;
	bcm2835_i2c_start_transfer(i2c_dev);
	}

	return IRQ_HANDLED;
	}

	if (val & BCM2835_I2C_S_RXR) {
	if (!i2c_dev->msg_buf_remaining) {
	i2c_dev->msg_err = val \| BCM2835_I2C_S_LEN;
	goto complete;
	}

	bcm2835_drain_rxfifo(i2c_dev);
	return IRQ_HANDLED;
	}

	return IRQ_NONE;

	complete:
	bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_C, BCM2835_I2C_C_CLEAR);
	bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_S, BCM2835_I2C_S_CLKT \|
	BCM2835_I2C_S_ERR \| BCM2835_I2C_S_DONE);
	complete(&i2c_dev->completion);

	return IRQ_HANDLED;
	}

	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);
	unsigned long time_left;
	int i, ret;

	for (i = 0; i < (num - 1); i++)
	if (msgs[i].flags & I2C_M_RD) {
	dev_warn_once(i2c_dev->dev,
	"only one read message supported, has to be last\n");
	return -EOPNOTSUPP;
	}

	ret = bcm2835_i2c_set_divider(i2c_dev);
	if (ret)
	return ret;

	i2c_dev->curr_msg = msgs;
	i2c_dev->num_msgs = num;
	reinit_completion(&i2c_dev->completion);

	bcm2835_i2c_start_transfer(i2c_dev);

	time_left = wait_for_completion_timeout(&i2c_dev->completion,
	adap->timeout);
	if (!time_left) {
	bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_C,
	BCM2835_I2C_C_CLEAR);
	dev_err(i2c_dev->dev, "i2c transfer timed out\n");
	return -ETIMEDOUT;
	}

	if (!i2c_dev->msg_err)
	return num;

	dev_dbg(i2c_dev->dev, "i2c transfer failed: %x\n", i2c_dev->msg_err);

	if (i2c_dev->msg_err & BCM2835_I2C_S_ERR)
	return -EREMOTEIO;

	return -EIO;
	}

	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,
	};

	/*
	* This HW was reported to have problems with clock stretching:
	* http://www.advamation.com/knowhow/raspberrypi/rpi-i2c-bug.html
	* https://www.raspberrypi.org/forums/viewtopic.php?p=146272
	*/
	static const struct i2c_adapter_quirks bcm2835_i2c_quirks = {
	.flags = I2C_AQ_NO_CLK_STRETCH,
	};

	static int bcm2835_i2c_probe(struct platform_device *pdev)
	{
	struct bcm2835_i2c_dev *i2c_dev;
	struct resource mem, irq;
	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)) {
	if (PTR_ERR(i2c_dev->clk) != -EPROBE_DEFER)
	dev_err(&pdev->dev, "Could not get clock\n");
	return PTR_ERR(i2c_dev->clk);
	}

	ret = of_property_read_u32(pdev->dev.of_node, "clock-frequency",
	&i2c_dev->bus_clk_rate);
	if (ret < 0) {
	dev_warn(&pdev->dev,
	"Could not read clock-frequency property\n");
	i2c_dev->bus_clk_rate = 100000;
	}

	irq = platform_get_resource(pdev, IORESOURCE_IRQ, 0);
	if (!irq) {
	dev_err(&pdev->dev, "No IRQ resource\n");
	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\n");
	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;
	adap->quirks = &bcm2835_i2c_quirks;

	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");