drivers/i2c/busses/i2c-mxs.c - nest-hello/linux-3.10 - Git at Google

 /*
  * Freescale MXS I2C bus driver
  *
  * Copyright (C) 2011-2012 Wolfram Sang, Pengutronix e.K.
  *
  * based on a (non-working) driver which was:
  *
  * Copyright (C) 2009-2010 Freescale Semiconductor, Inc. All Rights Reserved.
  *
  * 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.
  *
  */

 #include <linux/slab.h>
 #include <linux/device.h>
 #include <linux/module.h>
 #include <linux/i2c.h>
 #include <linux/err.h>
 #include <linux/interrupt.h>
 #include <linux/completion.h>
 #include <linux/platform_device.h>
 #include <linux/jiffies.h>
 #include <linux/io.h>
 #include <linux/pinctrl/consumer.h>
 #include <linux/stmp_device.h>
 #include <linux/of.h>
 #include <linux/of_device.h>
 #include <linux/of_i2c.h>
 #include <linux/dma-mapping.h>
 #include <linux/dmaengine.h>

 #define DRIVER_NAME "mxs-i2c"

 #define MXS_I2C_CTRL0		(0x00)
 #define MXS_I2C_CTRL0_SET	(0x04)

 #define MXS_I2C_CTRL0_SFTRST			0x80000000
 #define MXS_I2C_CTRL0_RUN			0x20000000
 #define MXS_I2C_CTRL0_SEND_NAK_ON_LAST		0x02000000
 #define MXS_I2C_CTRL0_RETAIN_CLOCK		0x00200000
 #define MXS_I2C_CTRL0_POST_SEND_STOP		0x00100000
 #define MXS_I2C_CTRL0_PRE_SEND_START		0x00080000
 #define MXS_I2C_CTRL0_MASTER_MODE		0x00020000
 #define MXS_I2C_CTRL0_DIRECTION			0x00010000
 #define MXS_I2C_CTRL0_XFER_COUNT(v)		((v) & 0x0000FFFF)

 #define MXS_I2C_TIMING0		(0x10)
 #define MXS_I2C_TIMING1		(0x20)
 #define MXS_I2C_TIMING2		(0x30)

 #define MXS_I2C_CTRL1		(0x40)
 #define MXS_I2C_CTRL1_SET	(0x44)
 #define MXS_I2C_CTRL1_CLR	(0x48)

 #define MXS_I2C_CTRL1_CLR_GOT_A_NAK		0x10000000
 #define MXS_I2C_CTRL1_BUS_FREE_IRQ		0x80
 #define MXS_I2C_CTRL1_DATA_ENGINE_CMPLT_IRQ	0x40
 #define MXS_I2C_CTRL1_NO_SLAVE_ACK_IRQ		0x20
 #define MXS_I2C_CTRL1_OVERSIZE_XFER_TERM_IRQ	0x10
 #define MXS_I2C_CTRL1_EARLY_TERM_IRQ		0x08
 #define MXS_I2C_CTRL1_MASTER_LOSS_IRQ		0x04
 #define MXS_I2C_CTRL1_SLAVE_STOP_IRQ		0x02
 #define MXS_I2C_CTRL1_SLAVE_IRQ			0x01

 #define MXS_I2C_STAT		(0x50)
 #define MXS_I2C_STAT_BUS_BUSY			0x00000800
 #define MXS_I2C_STAT_CLK_GEN_BUSY		0x00000400

 #define MXS_I2C_DATA		(0xa0)

 #define MXS_I2C_DEBUG0		(0xb0)
 #define MXS_I2C_DEBUG0_CLR	(0xb8)

 #define MXS_I2C_DEBUG0_DMAREQ	0x80000000

 #define MXS_I2C_IRQ_MASK	(MXS_I2C_CTRL1_DATA_ENGINE_CMPLT_IRQ | \
 				 MXS_I2C_CTRL1_NO_SLAVE_ACK_IRQ | \
 				 MXS_I2C_CTRL1_EARLY_TERM_IRQ | \
 				 MXS_I2C_CTRL1_MASTER_LOSS_IRQ | \
 				 MXS_I2C_CTRL1_SLAVE_STOP_IRQ | \
 				 MXS_I2C_CTRL1_SLAVE_IRQ)


 #define MXS_CMD_I2C_SELECT	(MXS_I2C_CTRL0_RETAIN_CLOCK |	\
 				 MXS_I2C_CTRL0_PRE_SEND_START |	\
 				 MXS_I2C_CTRL0_MASTER_MODE |	\
 				 MXS_I2C_CTRL0_DIRECTION |	\
 				 MXS_I2C_CTRL0_XFER_COUNT(1))

 #define MXS_CMD_I2C_WRITE	(MXS_I2C_CTRL0_PRE_SEND_START |	\
 				 MXS_I2C_CTRL0_MASTER_MODE |	\
 				 MXS_I2C_CTRL0_DIRECTION)

 #define MXS_CMD_I2C_READ	(MXS_I2C_CTRL0_SEND_NAK_ON_LAST | \
 				 MXS_I2C_CTRL0_MASTER_MODE)

 /**
  * struct mxs_i2c_dev - per device, private MXS-I2C data
  *
  * @dev: driver model device node
  * @regs: IO registers pointer
  * @cmd_complete: completion object for transaction wait
  * @cmd_err: error code for last transaction
  * @adapter: i2c subsystem adapter node
  */
 struct mxs_i2c_dev {
 	struct device *dev;
 	void __iomem *regs;
 	struct completion cmd_complete;
 	int cmd_err;
 	struct i2c_adapter adapter;

 	uint32_t timing0;
 	uint32_t timing1;

 	/* DMA support components */
 	struct dma_chan         	*dmach;
 	uint32_t			pio_data[2];
 	uint32_t			addr_data;
 	struct scatterlist		sg_io[2];
 	bool				dma_read;
 };

 static void mxs_i2c_reset(struct mxs_i2c_dev *i2c)
 {
 	stmp_reset_block(i2c->regs);

 	/*
 	 * Configure timing for the I2C block. The I2C TIMING2 register has to
 	 * be programmed with this particular magic number. The rest is derived
 	 * from the XTAL speed and requested I2C speed.
 	 *
 	 * For details, see i.MX233 [25.4.2 - 25.4.4] and i.MX28 [27.5.2 - 27.5.4].
 	 */
 	writel(i2c->timing0, i2c->regs + MXS_I2C_TIMING0);
 	writel(i2c->timing1, i2c->regs + MXS_I2C_TIMING1);
 	writel(0x00300030, i2c->regs + MXS_I2C_TIMING2);

 	writel(MXS_I2C_IRQ_MASK << 8, i2c->regs + MXS_I2C_CTRL1_SET);
 }

 static void mxs_i2c_dma_finish(struct mxs_i2c_dev *i2c)
 {
 	if (i2c->dma_read) {
 		dma_unmap_sg(i2c->dev, &i2c->sg_io[0], 1, DMA_TO_DEVICE);
 		dma_unmap_sg(i2c->dev, &i2c->sg_io[1], 1, DMA_FROM_DEVICE);
 	} else {
 		dma_unmap_sg(i2c->dev, i2c->sg_io, 2, DMA_TO_DEVICE);
 	}
 }

 static void mxs_i2c_dma_irq_callback(void *param)
 {
 	struct mxs_i2c_dev *i2c = param;

 	complete(&i2c->cmd_complete);
 	mxs_i2c_dma_finish(i2c);
 }

 static int mxs_i2c_dma_setup_xfer(struct i2c_adapter *adap,
 			struct i2c_msg *msg, uint32_t flags)
 {
 	struct dma_async_tx_descriptor *desc;
 	struct mxs_i2c_dev *i2c = i2c_get_adapdata(adap);

 	if (msg->flags & I2C_M_RD) {
 		i2c->dma_read = 1;
 		i2c->addr_data = (msg->addr << 1) | I2C_SMBUS_READ;

 		/*
 		 * SELECT command.
 		 */

 		/* Queue the PIO register write transfer. */
 		i2c->pio_data[0] = MXS_CMD_I2C_SELECT;
 		desc = dmaengine_prep_slave_sg(i2c->dmach,
 					(struct scatterlist *)&i2c->pio_data[0],
 					1, DMA_TRANS_NONE, 0);
 		if (!desc) {
 			dev_err(i2c->dev,
 				"Failed to get PIO reg. write descriptor.\n");
 			goto select_init_pio_fail;
 		}

 		/* Queue the DMA data transfer. */
 		sg_init_one(&i2c->sg_io[0], &i2c->addr_data, 1);
 		dma_map_sg(i2c->dev, &i2c->sg_io[0], 1, DMA_TO_DEVICE);
 		desc = dmaengine_prep_slave_sg(i2c->dmach, &i2c->sg_io[0], 1,
 					DMA_MEM_TO_DEV,
 					DMA_PREP_INTERRUPT | DMA_CTRL_ACK);
 		if (!desc) {
 			dev_err(i2c->dev,
 				"Failed to get DMA data write descriptor.\n");
 			goto select_init_dma_fail;
 		}

 		/*
 		 * READ command.
 		 */

 		/* Queue the PIO register write transfer. */
 		i2c->pio_data[1] = flags | MXS_CMD_I2C_READ |
 				MXS_I2C_CTRL0_XFER_COUNT(msg->len);
 		desc = dmaengine_prep_slave_sg(i2c->dmach,
 					(struct scatterlist *)&i2c->pio_data[1],
 					1, DMA_TRANS_NONE, DMA_PREP_INTERRUPT);
 		if (!desc) {
 			dev_err(i2c->dev,
 				"Failed to get PIO reg. write descriptor.\n");
 			goto select_init_dma_fail;
 		}

 		/* Queue the DMA data transfer. */
 		sg_init_one(&i2c->sg_io[1], msg->buf, msg->len);
 		dma_map_sg(i2c->dev, &i2c->sg_io[1], 1, DMA_FROM_DEVICE);
 		desc = dmaengine_prep_slave_sg(i2c->dmach, &i2c->sg_io[1], 1,
 					DMA_DEV_TO_MEM,
 					DMA_PREP_INTERRUPT | DMA_CTRL_ACK);
 		if (!desc) {
 			dev_err(i2c->dev,
 				"Failed to get DMA data write descriptor.\n");
 			goto read_init_dma_fail;
 		}
 	} else {
 		i2c->dma_read = 0;
 		i2c->addr_data = (msg->addr << 1) | I2C_SMBUS_WRITE;

 		/*
 		 * WRITE command.
 		 */

 		/* Queue the PIO register write transfer. */
 		i2c->pio_data[0] = flags | MXS_CMD_I2C_WRITE |
 				MXS_I2C_CTRL0_XFER_COUNT(msg->len + 1);
 		desc = dmaengine_prep_slave_sg(i2c->dmach,
 					(struct scatterlist *)&i2c->pio_data[0],
 					1, DMA_TRANS_NONE, 0);
 		if (!desc) {
 			dev_err(i2c->dev,
 				"Failed to get PIO reg. write descriptor.\n");
 			goto write_init_pio_fail;
 		}

 		/* Queue the DMA data transfer. */
 		sg_init_table(i2c->sg_io, 2);
 		sg_set_buf(&i2c->sg_io[0], &i2c->addr_data, 1);
 		sg_set_buf(&i2c->sg_io[1], msg->buf, msg->len);
 		dma_map_sg(i2c->dev, i2c->sg_io, 2, DMA_TO_DEVICE);
 		desc = dmaengine_prep_slave_sg(i2c->dmach, i2c->sg_io, 2,
 					DMA_MEM_TO_DEV,
 					DMA_PREP_INTERRUPT | DMA_CTRL_ACK);
 		if (!desc) {
 			dev_err(i2c->dev,
 				"Failed to get DMA data write descriptor.\n");
 			goto write_init_dma_fail;
 		}
 	}

 	/*
 	 * The last descriptor must have this callback,
 	 * to finish the DMA transaction.
 	 */
 	desc->callback = mxs_i2c_dma_irq_callback;
 	desc->callback_param = i2c;

 	/* Start the transfer. */
 	dmaengine_submit(desc);
 	dma_async_issue_pending(i2c->dmach);
 	return 0;

 /* Read failpath. */
 read_init_dma_fail:
 	dma_unmap_sg(i2c->dev, &i2c->sg_io[1], 1, DMA_FROM_DEVICE);
 select_init_dma_fail:
 	dma_unmap_sg(i2c->dev, &i2c->sg_io[0], 1, DMA_TO_DEVICE);
 select_init_pio_fail:
 	dmaengine_terminate_all(i2c->dmach);
 	return -EINVAL;

 /* Write failpath. */
 write_init_dma_fail:
 	dma_unmap_sg(i2c->dev, i2c->sg_io, 2, DMA_TO_DEVICE);
 write_init_pio_fail:
 	dmaengine_terminate_all(i2c->dmach);
 	return -EINVAL;
 }

 static int mxs_i2c_pio_wait_dmareq(struct mxs_i2c_dev *i2c)
 {
 	unsigned long timeout = jiffies + msecs_to_jiffies(1000);

 	while (!(readl(i2c->regs + MXS_I2C_DEBUG0) &
 		MXS_I2C_DEBUG0_DMAREQ)) {
 		if (time_after(jiffies, timeout))
 			return -ETIMEDOUT;
 		cond_resched();
 	}

 	return 0;
 }

 static int mxs_i2c_pio_wait_cplt(struct mxs_i2c_dev *i2c, int last)
 {
 	unsigned long timeout = jiffies + msecs_to_jiffies(1000);

 	/*
 	 * We do not use interrupts in the PIO mode. Due to the
 	 * maximum transfer length being 8 bytes in PIO mode, the
 	 * overhead of interrupt would be too large and this would
 	 * neglect the gain from using the PIO mode.
 	 */

 	while (!(readl(i2c->regs + MXS_I2C_CTRL1) &
 		MXS_I2C_CTRL1_DATA_ENGINE_CMPLT_IRQ)) {
 		if (time_after(jiffies, timeout))
 			return -ETIMEDOUT;
 		cond_resched();
 	}

 	writel(MXS_I2C_CTRL1_DATA_ENGINE_CMPLT_IRQ,
 		i2c->regs + MXS_I2C_CTRL1_CLR);

 	/*
 	 * When ending a transfer with a stop, we have to wait for the bus to
 	 * go idle before we report the transfer as completed. Otherwise the
 	 * start of the next transfer may race with the end of the current one.
 	 */
 	while (last && (readl(i2c->regs + MXS_I2C_STAT) &
 			(MXS_I2C_STAT_BUS_BUSY | MXS_I2C_STAT_CLK_GEN_BUSY))) {
 		if (time_after(jiffies, timeout))
 			return -ETIMEDOUT;
 		cond_resched();
 	}

 	return 0;
 }

 static int mxs_i2c_pio_check_error_state(struct mxs_i2c_dev *i2c)
 {
 	u32 state;

 	state = readl(i2c->regs + MXS_I2C_CTRL1_CLR) & MXS_I2C_IRQ_MASK;

 	if (state & MXS_I2C_CTRL1_NO_SLAVE_ACK_IRQ)
 		i2c->cmd_err = -ENXIO;
 	else if (state & (MXS_I2C_CTRL1_EARLY_TERM_IRQ |
 			  MXS_I2C_CTRL1_MASTER_LOSS_IRQ |
 			  MXS_I2C_CTRL1_SLAVE_STOP_IRQ |
 			  MXS_I2C_CTRL1_SLAVE_IRQ))
 		i2c->cmd_err = -EIO;

 	return i2c->cmd_err;
 }

 static void mxs_i2c_pio_trigger_cmd(struct mxs_i2c_dev *i2c, u32 cmd)
 {
 	u32 reg;

 	writel(cmd, i2c->regs + MXS_I2C_CTRL0);

 	/* readback makes sure the write is latched into hardware */
 	reg = readl(i2c->regs + MXS_I2C_CTRL0);
 	reg |= MXS_I2C_CTRL0_RUN;
 	writel(reg, i2c->regs + MXS_I2C_CTRL0);
 }

 static int mxs_i2c_pio_setup_xfer(struct i2c_adapter *adap,
 			struct i2c_msg *msg, uint32_t flags)
 {
 	struct mxs_i2c_dev *i2c = i2c_get_adapdata(adap);
 	uint32_t addr_data = msg->addr << 1;
 	uint32_t data = 0;
 	int i, shifts_left, ret;

 	/* Mute IRQs coming from this block. */
 	writel(MXS_I2C_IRQ_MASK << 8, i2c->regs + MXS_I2C_CTRL1_CLR);

 	if (msg->flags & I2C_M_RD) {
 		addr_data |= I2C_SMBUS_READ;

 		/* SELECT command. */
 		mxs_i2c_pio_trigger_cmd(i2c, MXS_CMD_I2C_SELECT);

 		ret = mxs_i2c_pio_wait_dmareq(i2c);
 		if (ret)
 			return ret;

 		writel(addr_data, i2c->regs + MXS_I2C_DATA);
 		writel(MXS_I2C_DEBUG0_DMAREQ, i2c->regs + MXS_I2C_DEBUG0_CLR);

 		ret = mxs_i2c_pio_wait_cplt(i2c, 0);
 		if (ret)
 			return ret;

 		if (mxs_i2c_pio_check_error_state(i2c))
 			goto cleanup;

 		/* READ command. */
 		mxs_i2c_pio_trigger_cmd(i2c,
 					MXS_CMD_I2C_READ | flags |
 					MXS_I2C_CTRL0_XFER_COUNT(msg->len));

 		for (i = 0; i < msg->len; i++) {
 			if ((i & 3) == 0) {
 				ret = mxs_i2c_pio_wait_dmareq(i2c);
 				if (ret)
 					return ret;
 				data = readl(i2c->regs + MXS_I2C_DATA);
 				writel(MXS_I2C_DEBUG0_DMAREQ,
 				       i2c->regs + MXS_I2C_DEBUG0_CLR);
 			}
 			msg->buf[i] = data & 0xff;
 			data >>= 8;
 		}
 	} else {
 		addr_data |= I2C_SMBUS_WRITE;

 		/* WRITE command. */
 		mxs_i2c_pio_trigger_cmd(i2c,
 					MXS_CMD_I2C_WRITE | flags |
 					MXS_I2C_CTRL0_XFER_COUNT(msg->len + 1));

 		/*
 		 * The LSB of data buffer is the first byte blasted across
 		 * the bus. Higher order bytes follow. Thus the following
 		 * filling schematic.
 		 */
 		data = addr_data << 24;
 		for (i = 0; i < msg->len; i++) {
 			data >>= 8;
 			data |= (msg->buf[i] << 24);
 			if ((i & 3) == 2) {
 				ret = mxs_i2c_pio_wait_dmareq(i2c);
 				if (ret)
 					return ret;
 				writel(data, i2c->regs + MXS_I2C_DATA);
 				writel(MXS_I2C_DEBUG0_DMAREQ,
 				       i2c->regs + MXS_I2C_DEBUG0_CLR);
 			}
 		}

 		shifts_left = 24 - (i & 3) * 8;
 		if (shifts_left) {
 			data >>= shifts_left;
 			ret = mxs_i2c_pio_wait_dmareq(i2c);
 			if (ret)
 				return ret;
 			writel(data, i2c->regs + MXS_I2C_DATA);
 			writel(MXS_I2C_DEBUG0_DMAREQ,
 			       i2c->regs + MXS_I2C_DEBUG0_CLR);
 		}
 	}

 	ret = mxs_i2c_pio_wait_cplt(i2c, flags & MXS_I2C_CTRL0_POST_SEND_STOP);
 	if (ret)
 		return ret;

 	/* make sure we capture any occurred error into cmd_err */
 	mxs_i2c_pio_check_error_state(i2c);

 cleanup:
 	/* Clear any dangling IRQs and re-enable interrupts. */
 	writel(MXS_I2C_IRQ_MASK, i2c->regs + MXS_I2C_CTRL1_CLR);
 	writel(MXS_I2C_IRQ_MASK << 8, i2c->regs + MXS_I2C_CTRL1_SET);

 	return 0;
 }

 /*
  * Low level master read/write transaction.
  */
 static int mxs_i2c_xfer_msg(struct i2c_adapter *adap, struct i2c_msg *msg,
 				int stop)
 {
 	struct mxs_i2c_dev *i2c = i2c_get_adapdata(adap);
 	int ret;
 	int flags;

 	flags = stop ? MXS_I2C_CTRL0_POST_SEND_STOP : 0;

 	dev_dbg(i2c->dev, "addr: 0x%04x, len: %d, flags: 0x%x, stop: %d\n",
 		msg->addr, msg->len, msg->flags, stop);

 	if (msg->len == 0)
 		return -EINVAL;

 	/*
 	 * The current boundary to select between PIO/DMA transfer method
 	 * is set to 8 bytes, transfers shorter than 8 bytes are transfered
 	 * using PIO mode while longer transfers use DMA. The 8 byte border is
 	 * based on this empirical measurement and a lot of previous frobbing.
 	 */
 	i2c->cmd_err = 0;
 	if (0) {	/* disable PIO mode until a proper fix is made */
 		ret = mxs_i2c_pio_setup_xfer(adap, msg, flags);
 		if (ret)
 			mxs_i2c_reset(i2c);
 	} else {
 		INIT_COMPLETION(i2c->cmd_complete);
 		ret = mxs_i2c_dma_setup_xfer(adap, msg, flags);
 		if (ret)
 			return ret;

 		ret = wait_for_completion_timeout(&i2c->cmd_complete,
 						msecs_to_jiffies(1000));
 		if (ret == 0)
 			goto timeout;
 	}

 	if (i2c->cmd_err == -ENXIO) {
 		/*
 		 * If the transfer fails with a NAK from the slave the
 		 * controller halts until it gets told to return to idle state.
 		 */
 		writel(MXS_I2C_CTRL1_CLR_GOT_A_NAK,
 		       i2c->regs + MXS_I2C_CTRL1_SET);
 	}

 	ret = i2c->cmd_err;

 	dev_dbg(i2c->dev, "Done with err=%d\n", ret);

 	return ret;

 timeout:
 	dev_dbg(i2c->dev, "Timeout!\n");
 	mxs_i2c_dma_finish(i2c);
 	mxs_i2c_reset(i2c);
 	return -ETIMEDOUT;
 }

 static int mxs_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg msgs[],
 			int num)
 {
 	int i;
 	int err;

 	for (i = 0; i < num; i++) {
 		err = mxs_i2c_xfer_msg(adap, &msgs[i], i == (num - 1));
 		if (err)
 			return err;
 	}

 	return num;
 }

 static u32 mxs_i2c_func(struct i2c_adapter *adap)
 {
 	return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL;
 }

 static irqreturn_t mxs_i2c_isr(int this_irq, void *dev_id)
 {
 	struct mxs_i2c_dev *i2c = dev_id;
 	u32 stat = readl(i2c->regs + MXS_I2C_CTRL1) & MXS_I2C_IRQ_MASK;

 	if (!stat)
 		return IRQ_NONE;

 	if (stat & MXS_I2C_CTRL1_NO_SLAVE_ACK_IRQ)
 		i2c->cmd_err = -ENXIO;
 	else if (stat & (MXS_I2C_CTRL1_EARLY_TERM_IRQ |
 		    MXS_I2C_CTRL1_MASTER_LOSS_IRQ |
 		    MXS_I2C_CTRL1_SLAVE_STOP_IRQ | MXS_I2C_CTRL1_SLAVE_IRQ))
 		/* MXS_I2C_CTRL1_OVERSIZE_XFER_TERM_IRQ is only for slaves */
 		i2c->cmd_err = -EIO;

 	writel(stat, i2c->regs + MXS_I2C_CTRL1_CLR);

 	return IRQ_HANDLED;
 }

 static const struct i2c_algorithm mxs_i2c_algo = {
 	.master_xfer = mxs_i2c_xfer,
 	.functionality = mxs_i2c_func,
 };

 static void mxs_i2c_derive_timing(struct mxs_i2c_dev *i2c, int speed)
 {
 	/* The I2C block clock run at 24MHz */
 	const uint32_t clk = 24000000;
 	uint32_t base;
 	uint16_t high_count, low_count, rcv_count, xmit_count;
 	struct device *dev = i2c->dev;

 	if (speed > 540000) {
 		dev_warn(dev, "Speed too high (%d Hz), using 540 kHz\n", speed);
 		speed = 540000;
 	} else if (speed < 12000) {
 		dev_warn(dev, "Speed too low (%d Hz), using 12 kHz\n", speed);
 		speed = 12000;
 	}

 	/*
 	 * The timing derivation algorithm. There is no documentation for this
 	 * algorithm available, it was derived by using the scope and fiddling
 	 * with constants until the result observed on the scope was good enough
 	 * for 20kHz, 50kHz, 100kHz, 200kHz, 300kHz and 400kHz. It should be
 	 * possible to assume the algorithm works for other frequencies as well.
 	 *
 	 * Note it was necessary to cap the frequency on both ends as it's not
 	 * possible to configure completely arbitrary frequency for the I2C bus
 	 * clock.
 	 */
 	base = ((clk / speed) - 38) / 2;
 	high_count = base + 3;
 	low_count = base - 3;
 	rcv_count = (high_count * 3) / 4;
 	xmit_count = low_count / 4;

 	i2c->timing0 = (high_count << 16) | rcv_count;
 	i2c->timing1 = (low_count << 16) | xmit_count;
 }

 static int mxs_i2c_get_ofdata(struct mxs_i2c_dev *i2c)
 {
 	uint32_t speed;
 	struct device *dev = i2c->dev;
 	struct device_node *node = dev->of_node;
 	int ret;

 	ret = of_property_read_u32(node, "clock-frequency", &speed);
 	if (ret) {
 		dev_warn(dev, "No I2C speed selected, using 100kHz\n");
 		speed = 100000;
 	}

 	mxs_i2c_derive_timing(i2c, speed);

 	return 0;
 }

 static int mxs_i2c_probe(struct platform_device *pdev)
 {
 	struct device *dev = &pdev->dev;
 	struct mxs_i2c_dev *i2c;
 	struct i2c_adapter *adap;
 	struct pinctrl *pinctrl;
 	struct resource *res;
 	resource_size_t res_size;
 	int err, irq;

 	pinctrl = devm_pinctrl_get_select_default(dev);
 	if (IS_ERR(pinctrl))
 		return PTR_ERR(pinctrl);

 	i2c = devm_kzalloc(dev, sizeof(struct mxs_i2c_dev), GFP_KERNEL);
 	if (!i2c)
 		return -ENOMEM;

 	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
 	irq = platform_get_irq(pdev, 0);

 	if (!res || irq < 0)
 		return -ENOENT;

 	res_size = resource_size(res);
 	if (!devm_request_mem_region(dev, res->start, res_size, res->name))
 		return -EBUSY;

 	i2c->regs = devm_ioremap_nocache(dev, res->start, res_size);
 	if (!i2c->regs)
 		return -EBUSY;

 	err = devm_request_irq(dev, irq, mxs_i2c_isr, 0, dev_name(dev), i2c);
 	if (err)
 		return err;

 	i2c->dev = dev;

 	init_completion(&i2c->cmd_complete);

 	if (dev->of_node) {
 		err = mxs_i2c_get_ofdata(i2c);
 		if (err)
 			return err;
 	}

 	/* Setup the DMA */
 	i2c->dmach = dma_request_slave_channel(dev, "rx-tx");
 	if (!i2c->dmach) {
 		dev_err(dev, "Failed to request dma\n");
 		return -ENODEV;
 	}

 	platform_set_drvdata(pdev, i2c);

 	/* Do reset to enforce correct startup after pinmuxing */
 	mxs_i2c_reset(i2c);

 	adap = &i2c->adapter;
 	strlcpy(adap->name, "MXS I2C adapter", sizeof(adap->name));
 	adap->owner = THIS_MODULE;
 	adap->algo = &mxs_i2c_algo;
 	adap->dev.parent = dev;
 	adap->nr = pdev->id;
 	adap->dev.of_node = pdev->dev.of_node;
 	i2c_set_adapdata(adap, i2c);
 	err = i2c_add_numbered_adapter(adap);
 	if (err) {
 		dev_err(dev, "Failed to add adapter (%d)\n", err);
 		writel(MXS_I2C_CTRL0_SFTRST,
 				i2c->regs + MXS_I2C_CTRL0_SET);
 		return err;
 	}

 	of_i2c_register_devices(adap);

 	return 0;
 }

 static int mxs_i2c_remove(struct platform_device *pdev)
 {
 	struct mxs_i2c_dev *i2c = platform_get_drvdata(pdev);

 	i2c_del_adapter(&i2c->adapter);

 	if (i2c->dmach)
 		dma_release_channel(i2c->dmach);

 	writel(MXS_I2C_CTRL0_SFTRST, i2c->regs + MXS_I2C_CTRL0_SET);

 	return 0;
 }

 static const struct of_device_id mxs_i2c_dt_ids[] = {
 	{ .compatible = "fsl,imx28-i2c", },
 	{ /* sentinel */ }
 };
 MODULE_DEVICE_TABLE(of, mxs_i2c_dt_ids);

 static struct platform_driver mxs_i2c_driver = {
 	.driver = {
 		   .name = DRIVER_NAME,
 		   .owner = THIS_MODULE,
 		   .of_match_table = mxs_i2c_dt_ids,
 		   },
 	.remove = mxs_i2c_remove,
 };

 static int __init mxs_i2c_init(void)
 {
 	return platform_driver_probe(&mxs_i2c_driver, mxs_i2c_probe);
 }
 subsys_initcall(mxs_i2c_init);

 static void __exit mxs_i2c_exit(void)
 {
 	platform_driver_unregister(&mxs_i2c_driver);
 }
 module_exit(mxs_i2c_exit);

 MODULE_AUTHOR("Wolfram Sang <w.sang@pengutronix.de>");
 MODULE_DESCRIPTION("MXS I2C Bus Driver");
 MODULE_LICENSE("GPL");
 MODULE_ALIAS("platform:" DRIVER_NAME);
	/*
	* Freescale MXS I2C bus driver
	*
	* Copyright (C) 2011-2012 Wolfram Sang, Pengutronix e.K.
	*
	* based on a (non-working) driver which was:
	*
	* Copyright (C) 2009-2010 Freescale Semiconductor, Inc. All Rights Reserved.
	*
	* 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.
	*
	*/

	#include <linux/slab.h>
	#include <linux/device.h>
	#include <linux/module.h>
	#include <linux/i2c.h>
	#include <linux/err.h>
	#include <linux/interrupt.h>
	#include <linux/completion.h>
	#include <linux/platform_device.h>
	#include <linux/jiffies.h>
	#include <linux/io.h>
	#include <linux/pinctrl/consumer.h>
	#include <linux/stmp_device.h>
	#include <linux/of.h>
	#include <linux/of_device.h>
	#include <linux/of_i2c.h>
	#include <linux/dma-mapping.h>
	#include <linux/dmaengine.h>

	#define DRIVER_NAME "mxs-i2c"

	#define MXS_I2C_CTRL0 (0x00)
	#define MXS_I2C_CTRL0_SET (0x04)

	#define MXS_I2C_CTRL0_SFTRST 0x80000000
	#define MXS_I2C_CTRL0_RUN 0x20000000
	#define MXS_I2C_CTRL0_SEND_NAK_ON_LAST 0x02000000
	#define MXS_I2C_CTRL0_RETAIN_CLOCK 0x00200000
	#define MXS_I2C_CTRL0_POST_SEND_STOP 0x00100000
	#define MXS_I2C_CTRL0_PRE_SEND_START 0x00080000
	#define MXS_I2C_CTRL0_MASTER_MODE 0x00020000
	#define MXS_I2C_CTRL0_DIRECTION 0x00010000
	#define MXS_I2C_CTRL0_XFER_COUNT(v) ((v) & 0x0000FFFF)

	#define MXS_I2C_TIMING0 (0x10)
	#define MXS_I2C_TIMING1 (0x20)
	#define MXS_I2C_TIMING2 (0x30)

	#define MXS_I2C_CTRL1 (0x40)
	#define MXS_I2C_CTRL1_SET (0x44)
	#define MXS_I2C_CTRL1_CLR (0x48)

	#define MXS_I2C_CTRL1_CLR_GOT_A_NAK 0x10000000
	#define MXS_I2C_CTRL1_BUS_FREE_IRQ 0x80
	#define MXS_I2C_CTRL1_DATA_ENGINE_CMPLT_IRQ 0x40
	#define MXS_I2C_CTRL1_NO_SLAVE_ACK_IRQ 0x20
	#define MXS_I2C_CTRL1_OVERSIZE_XFER_TERM_IRQ 0x10
	#define MXS_I2C_CTRL1_EARLY_TERM_IRQ 0x08
	#define MXS_I2C_CTRL1_MASTER_LOSS_IRQ 0x04
	#define MXS_I2C_CTRL1_SLAVE_STOP_IRQ 0x02
	#define MXS_I2C_CTRL1_SLAVE_IRQ 0x01

	#define MXS_I2C_STAT (0x50)
	#define MXS_I2C_STAT_BUS_BUSY 0x00000800
	#define MXS_I2C_STAT_CLK_GEN_BUSY 0x00000400

	#define MXS_I2C_DATA (0xa0)

	#define MXS_I2C_DEBUG0 (0xb0)
	#define MXS_I2C_DEBUG0_CLR (0xb8)

	#define MXS_I2C_DEBUG0_DMAREQ 0x80000000

	#define MXS_I2C_IRQ_MASK (MXS_I2C_CTRL1_DATA_ENGINE_CMPLT_IRQ \| \
	MXS_I2C_CTRL1_NO_SLAVE_ACK_IRQ \| \
	MXS_I2C_CTRL1_EARLY_TERM_IRQ \| \
	MXS_I2C_CTRL1_MASTER_LOSS_IRQ \| \
	MXS_I2C_CTRL1_SLAVE_STOP_IRQ \| \
	MXS_I2C_CTRL1_SLAVE_IRQ)


	#define MXS_CMD_I2C_SELECT (MXS_I2C_CTRL0_RETAIN_CLOCK \| \
	MXS_I2C_CTRL0_PRE_SEND_START \| \
	MXS_I2C_CTRL0_MASTER_MODE \| \
	MXS_I2C_CTRL0_DIRECTION \| \
	MXS_I2C_CTRL0_XFER_COUNT(1))

	#define MXS_CMD_I2C_WRITE (MXS_I2C_CTRL0_PRE_SEND_START \| \
	MXS_I2C_CTRL0_MASTER_MODE \| \
	MXS_I2C_CTRL0_DIRECTION)

	#define MXS_CMD_I2C_READ (MXS_I2C_CTRL0_SEND_NAK_ON_LAST \| \
	MXS_I2C_CTRL0_MASTER_MODE)

	/**
	* struct mxs_i2c_dev - per device, private MXS-I2C data
	*
	* @dev: driver model device node
	* @regs: IO registers pointer
	* @cmd_complete: completion object for transaction wait
	* @cmd_err: error code for last transaction
	* @adapter: i2c subsystem adapter node
	*/
	struct mxs_i2c_dev {
	struct device *dev;
	void __iomem *regs;
	struct completion cmd_complete;
	int cmd_err;
	struct i2c_adapter adapter;

	uint32_t timing0;
	uint32_t timing1;

	/* DMA support components */
	struct dma_chan *dmach;
	uint32_t pio_data[2];
	uint32_t addr_data;
	struct scatterlist sg_io[2];
	bool dma_read;
	};

	static void mxs_i2c_reset(struct mxs_i2c_dev *i2c)
	{
	stmp_reset_block(i2c->regs);

	/*
	* Configure timing for the I2C block. The I2C TIMING2 register has to
	* be programmed with this particular magic number. The rest is derived
	* from the XTAL speed and requested I2C speed.
	*
	* For details, see i.MX233 [25.4.2 - 25.4.4] and i.MX28 [27.5.2 - 27.5.4].
	*/
	writel(i2c->timing0, i2c->regs + MXS_I2C_TIMING0);
	writel(i2c->timing1, i2c->regs + MXS_I2C_TIMING1);
	writel(0x00300030, i2c->regs + MXS_I2C_TIMING2);

	writel(MXS_I2C_IRQ_MASK << 8, i2c->regs + MXS_I2C_CTRL1_SET);
	}

	static void mxs_i2c_dma_finish(struct mxs_i2c_dev *i2c)
	{
	if (i2c->dma_read) {
	dma_unmap_sg(i2c->dev, &i2c->sg_io[0], 1, DMA_TO_DEVICE);
	dma_unmap_sg(i2c->dev, &i2c->sg_io[1], 1, DMA_FROM_DEVICE);
	} else {
	dma_unmap_sg(i2c->dev, i2c->sg_io, 2, DMA_TO_DEVICE);
	}
	}

	static void mxs_i2c_dma_irq_callback(void *param)
	{
	struct mxs_i2c_dev *i2c = param;

	complete(&i2c->cmd_complete);
	mxs_i2c_dma_finish(i2c);
	}

	static int mxs_i2c_dma_setup_xfer(struct i2c_adapter *adap,
	struct i2c_msg *msg, uint32_t flags)
	{
	struct dma_async_tx_descriptor *desc;
	struct mxs_i2c_dev *i2c = i2c_get_adapdata(adap);

	if (msg->flags & I2C_M_RD) {
	i2c->dma_read = 1;
	i2c->addr_data = (msg->addr << 1) \| I2C_SMBUS_READ;

	/*
	* SELECT command.
	*/

	/* Queue the PIO register write transfer. */
	i2c->pio_data[0] = MXS_CMD_I2C_SELECT;
	desc = dmaengine_prep_slave_sg(i2c->dmach,
	(struct scatterlist *)&i2c->pio_data[0],
	1, DMA_TRANS_NONE, 0);
	if (!desc) {
	dev_err(i2c->dev,
	"Failed to get PIO reg. write descriptor.\n");
	goto select_init_pio_fail;
	}

	/* Queue the DMA data transfer. */
	sg_init_one(&i2c->sg_io[0], &i2c->addr_data, 1);
	dma_map_sg(i2c->dev, &i2c->sg_io[0], 1, DMA_TO_DEVICE);
	desc = dmaengine_prep_slave_sg(i2c->dmach, &i2c->sg_io[0], 1,
	DMA_MEM_TO_DEV,
	DMA_PREP_INTERRUPT \| DMA_CTRL_ACK);
	if (!desc) {
	dev_err(i2c->dev,
	"Failed to get DMA data write descriptor.\n");
	goto select_init_dma_fail;
	}

	/*
	* READ command.
	*/

	/* Queue the PIO register write transfer. */
	i2c->pio_data[1] = flags \| MXS_CMD_I2C_READ \|
	MXS_I2C_CTRL0_XFER_COUNT(msg->len);
	desc = dmaengine_prep_slave_sg(i2c->dmach,
	(struct scatterlist *)&i2c->pio_data[1],
	1, DMA_TRANS_NONE, DMA_PREP_INTERRUPT);
	if (!desc) {
	dev_err(i2c->dev,
	"Failed to get PIO reg. write descriptor.\n");
	goto select_init_dma_fail;
	}

	/* Queue the DMA data transfer. */
	sg_init_one(&i2c->sg_io[1], msg->buf, msg->len);
	dma_map_sg(i2c->dev, &i2c->sg_io[1], 1, DMA_FROM_DEVICE);
	desc = dmaengine_prep_slave_sg(i2c->dmach, &i2c->sg_io[1], 1,
	DMA_DEV_TO_MEM,
	DMA_PREP_INTERRUPT \| DMA_CTRL_ACK);
	if (!desc) {
	dev_err(i2c->dev,
	"Failed to get DMA data write descriptor.\n");
	goto read_init_dma_fail;
	}
	} else {
	i2c->dma_read = 0;
	i2c->addr_data = (msg->addr << 1) \| I2C_SMBUS_WRITE;

	/*
	* WRITE command.
	*/

	/* Queue the PIO register write transfer. */
	i2c->pio_data[0] = flags \| MXS_CMD_I2C_WRITE \|
	MXS_I2C_CTRL0_XFER_COUNT(msg->len + 1);
	desc = dmaengine_prep_slave_sg(i2c->dmach,
	(struct scatterlist *)&i2c->pio_data[0],
	1, DMA_TRANS_NONE, 0);
	if (!desc) {
	dev_err(i2c->dev,
	"Failed to get PIO reg. write descriptor.\n");
	goto write_init_pio_fail;
	}

	/* Queue the DMA data transfer. */
	sg_init_table(i2c->sg_io, 2);
	sg_set_buf(&i2c->sg_io[0], &i2c->addr_data, 1);
	sg_set_buf(&i2c->sg_io[1], msg->buf, msg->len);
	dma_map_sg(i2c->dev, i2c->sg_io, 2, DMA_TO_DEVICE);
	desc = dmaengine_prep_slave_sg(i2c->dmach, i2c->sg_io, 2,
	DMA_MEM_TO_DEV,
	DMA_PREP_INTERRUPT \| DMA_CTRL_ACK);
	if (!desc) {
	dev_err(i2c->dev,
	"Failed to get DMA data write descriptor.\n");
	goto write_init_dma_fail;
	}
	}

	/*
	* The last descriptor must have this callback,
	* to finish the DMA transaction.
	*/
	desc->callback = mxs_i2c_dma_irq_callback;
	desc->callback_param = i2c;

	/* Start the transfer. */
	dmaengine_submit(desc);
	dma_async_issue_pending(i2c->dmach);
	return 0;

	/* Read failpath. */
	read_init_dma_fail:
	dma_unmap_sg(i2c->dev, &i2c->sg_io[1], 1, DMA_FROM_DEVICE);
	select_init_dma_fail:
	dma_unmap_sg(i2c->dev, &i2c->sg_io[0], 1, DMA_TO_DEVICE);
	select_init_pio_fail:
	dmaengine_terminate_all(i2c->dmach);
	return -EINVAL;

	/* Write failpath. */
	write_init_dma_fail:
	dma_unmap_sg(i2c->dev, i2c->sg_io, 2, DMA_TO_DEVICE);
	write_init_pio_fail:
	dmaengine_terminate_all(i2c->dmach);
	return -EINVAL;
	}

	static int mxs_i2c_pio_wait_dmareq(struct mxs_i2c_dev *i2c)
	{
	unsigned long timeout = jiffies + msecs_to_jiffies(1000);

	while (!(readl(i2c->regs + MXS_I2C_DEBUG0) &
	MXS_I2C_DEBUG0_DMAREQ)) {
	if (time_after(jiffies, timeout))
	return -ETIMEDOUT;
	cond_resched();
	}

	return 0;
	}

	static int mxs_i2c_pio_wait_cplt(struct mxs_i2c_dev *i2c, int last)
	{
	unsigned long timeout = jiffies + msecs_to_jiffies(1000);

	/*
	* We do not use interrupts in the PIO mode. Due to the
	* maximum transfer length being 8 bytes in PIO mode, the
	* overhead of interrupt would be too large and this would
	* neglect the gain from using the PIO mode.
	*/

	while (!(readl(i2c->regs + MXS_I2C_CTRL1) &
	MXS_I2C_CTRL1_DATA_ENGINE_CMPLT_IRQ)) {
	if (time_after(jiffies, timeout))
	return -ETIMEDOUT;
	cond_resched();
	}

	writel(MXS_I2C_CTRL1_DATA_ENGINE_CMPLT_IRQ,
	i2c->regs + MXS_I2C_CTRL1_CLR);

	/*
	* When ending a transfer with a stop, we have to wait for the bus to
	* go idle before we report the transfer as completed. Otherwise the
	* start of the next transfer may race with the end of the current one.
	*/
	while (last && (readl(i2c->regs + MXS_I2C_STAT) &
	(MXS_I2C_STAT_BUS_BUSY \| MXS_I2C_STAT_CLK_GEN_BUSY))) {
	if (time_after(jiffies, timeout))
	return -ETIMEDOUT;
	cond_resched();
	}

	return 0;
	}

	static int mxs_i2c_pio_check_error_state(struct mxs_i2c_dev *i2c)
	{
	u32 state;

	state = readl(i2c->regs + MXS_I2C_CTRL1_CLR) & MXS_I2C_IRQ_MASK;

	if (state & MXS_I2C_CTRL1_NO_SLAVE_ACK_IRQ)
	i2c->cmd_err = -ENXIO;
	else if (state & (MXS_I2C_CTRL1_EARLY_TERM_IRQ \|
	MXS_I2C_CTRL1_MASTER_LOSS_IRQ \|
	MXS_I2C_CTRL1_SLAVE_STOP_IRQ \|
	MXS_I2C_CTRL1_SLAVE_IRQ))
	i2c->cmd_err = -EIO;

	return i2c->cmd_err;
	}

	static void mxs_i2c_pio_trigger_cmd(struct mxs_i2c_dev *i2c, u32 cmd)
	{
	u32 reg;

	writel(cmd, i2c->regs + MXS_I2C_CTRL0);

	/* readback makes sure the write is latched into hardware */
	reg = readl(i2c->regs + MXS_I2C_CTRL0);
	reg \|= MXS_I2C_CTRL0_RUN;
	writel(reg, i2c->regs + MXS_I2C_CTRL0);
	}

	static int mxs_i2c_pio_setup_xfer(struct i2c_adapter *adap,
	struct i2c_msg *msg, uint32_t flags)
	{
	struct mxs_i2c_dev *i2c = i2c_get_adapdata(adap);
	uint32_t addr_data = msg->addr << 1;
	uint32_t data = 0;
	int i, shifts_left, ret;

	/* Mute IRQs coming from this block. */
	writel(MXS_I2C_IRQ_MASK << 8, i2c->regs + MXS_I2C_CTRL1_CLR);

	if (msg->flags & I2C_M_RD) {
	addr_data \|= I2C_SMBUS_READ;

	/* SELECT command. */
	mxs_i2c_pio_trigger_cmd(i2c, MXS_CMD_I2C_SELECT);

	ret = mxs_i2c_pio_wait_dmareq(i2c);
	if (ret)
	return ret;

	writel(addr_data, i2c->regs + MXS_I2C_DATA);
	writel(MXS_I2C_DEBUG0_DMAREQ, i2c->regs + MXS_I2C_DEBUG0_CLR);

	ret = mxs_i2c_pio_wait_cplt(i2c, 0);
	if (ret)
	return ret;

	if (mxs_i2c_pio_check_error_state(i2c))
	goto cleanup;

	/* READ command. */
	mxs_i2c_pio_trigger_cmd(i2c,
	MXS_CMD_I2C_READ \| flags \|
	MXS_I2C_CTRL0_XFER_COUNT(msg->len));

	for (i = 0; i < msg->len; i++) {
	if ((i & 3) == 0) {
	ret = mxs_i2c_pio_wait_dmareq(i2c);
	if (ret)
	return ret;
	data = readl(i2c->regs + MXS_I2C_DATA);
	writel(MXS_I2C_DEBUG0_DMAREQ,
	i2c->regs + MXS_I2C_DEBUG0_CLR);
	}
	msg->buf[i] = data & 0xff;
	data >>= 8;
	}
	} else {
	addr_data \|= I2C_SMBUS_WRITE;

	/* WRITE command. */
	mxs_i2c_pio_trigger_cmd(i2c,
	MXS_CMD_I2C_WRITE \| flags \|
	MXS_I2C_CTRL0_XFER_COUNT(msg->len + 1));

	/*
	* The LSB of data buffer is the first byte blasted across
	* the bus. Higher order bytes follow. Thus the following
	* filling schematic.
	*/
	data = addr_data << 24;
	for (i = 0; i < msg->len; i++) {
	data >>= 8;
	data \|= (msg->buf[i] << 24);
	if ((i & 3) == 2) {
	ret = mxs_i2c_pio_wait_dmareq(i2c);
	if (ret)
	return ret;
	writel(data, i2c->regs + MXS_I2C_DATA);
	writel(MXS_I2C_DEBUG0_DMAREQ,
	i2c->regs + MXS_I2C_DEBUG0_CLR);
	}
	}

	shifts_left = 24 - (i & 3) * 8;
	if (shifts_left) {
	data >>= shifts_left;
	ret = mxs_i2c_pio_wait_dmareq(i2c);
	if (ret)
	return ret;
	writel(data, i2c->regs + MXS_I2C_DATA);
	writel(MXS_I2C_DEBUG0_DMAREQ,
	i2c->regs + MXS_I2C_DEBUG0_CLR);
	}
	}

	ret = mxs_i2c_pio_wait_cplt(i2c, flags & MXS_I2C_CTRL0_POST_SEND_STOP);
	if (ret)
	return ret;

	/* make sure we capture any occurred error into cmd_err */
	mxs_i2c_pio_check_error_state(i2c);

	cleanup:
	/* Clear any dangling IRQs and re-enable interrupts. */
	writel(MXS_I2C_IRQ_MASK, i2c->regs + MXS_I2C_CTRL1_CLR);
	writel(MXS_I2C_IRQ_MASK << 8, i2c->regs + MXS_I2C_CTRL1_SET);

	return 0;
	}

	/*
	* Low level master read/write transaction.
	*/
	static int mxs_i2c_xfer_msg(struct i2c_adapter adap, struct i2c_msg msg,
	int stop)
	{
	struct mxs_i2c_dev *i2c = i2c_get_adapdata(adap);
	int ret;
	int flags;

	flags = stop ? MXS_I2C_CTRL0_POST_SEND_STOP : 0;

	dev_dbg(i2c->dev, "addr: 0x%04x, len: %d, flags: 0x%x, stop: %d\n",
	msg->addr, msg->len, msg->flags, stop);

	if (msg->len == 0)
	return -EINVAL;

	/*
	* The current boundary to select between PIO/DMA transfer method
	* is set to 8 bytes, transfers shorter than 8 bytes are transfered
	* using PIO mode while longer transfers use DMA. The 8 byte border is
	* based on this empirical measurement and a lot of previous frobbing.
	*/
	i2c->cmd_err = 0;
	if (0) { /* disable PIO mode until a proper fix is made */
	ret = mxs_i2c_pio_setup_xfer(adap, msg, flags);
	if (ret)
	mxs_i2c_reset(i2c);
	} else {
	INIT_COMPLETION(i2c->cmd_complete);
	ret = mxs_i2c_dma_setup_xfer(adap, msg, flags);
	if (ret)
	return ret;

	ret = wait_for_completion_timeout(&i2c->cmd_complete,
	msecs_to_jiffies(1000));
	if (ret == 0)
	goto timeout;
	}

	if (i2c->cmd_err == -ENXIO) {
	/*
	* If the transfer fails with a NAK from the slave the
	* controller halts until it gets told to return to idle state.
	*/
	writel(MXS_I2C_CTRL1_CLR_GOT_A_NAK,
	i2c->regs + MXS_I2C_CTRL1_SET);
	}

	ret = i2c->cmd_err;

	dev_dbg(i2c->dev, "Done with err=%d\n", ret);

	return ret;

	timeout:
	dev_dbg(i2c->dev, "Timeout!\n");
	mxs_i2c_dma_finish(i2c);
	mxs_i2c_reset(i2c);
	return -ETIMEDOUT;
	}

	static int mxs_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg msgs[],
	int num)
	{
	int i;
	int err;

	for (i = 0; i < num; i++) {
	err = mxs_i2c_xfer_msg(adap, &msgs[i], i == (num - 1));
	if (err)
	return err;
	}

	return num;
	}

	static u32 mxs_i2c_func(struct i2c_adapter *adap)
	{
	return I2C_FUNC_I2C \| I2C_FUNC_SMBUS_EMUL;
	}

	static irqreturn_t mxs_i2c_isr(int this_irq, void *dev_id)
	{
	struct mxs_i2c_dev *i2c = dev_id;
	u32 stat = readl(i2c->regs + MXS_I2C_CTRL1) & MXS_I2C_IRQ_MASK;

	if (!stat)
	return IRQ_NONE;

	if (stat & MXS_I2C_CTRL1_NO_SLAVE_ACK_IRQ)
	i2c->cmd_err = -ENXIO;
	else if (stat & (MXS_I2C_CTRL1_EARLY_TERM_IRQ \|
	MXS_I2C_CTRL1_MASTER_LOSS_IRQ \|
	MXS_I2C_CTRL1_SLAVE_STOP_IRQ \| MXS_I2C_CTRL1_SLAVE_IRQ))
	/* MXS_I2C_CTRL1_OVERSIZE_XFER_TERM_IRQ is only for slaves */
	i2c->cmd_err = -EIO;

	writel(stat, i2c->regs + MXS_I2C_CTRL1_CLR);

	return IRQ_HANDLED;
	}

	static const struct i2c_algorithm mxs_i2c_algo = {
	.master_xfer = mxs_i2c_xfer,
	.functionality = mxs_i2c_func,
	};

	static void mxs_i2c_derive_timing(struct mxs_i2c_dev *i2c, int speed)
	{
	/* The I2C block clock run at 24MHz */
	const uint32_t clk = 24000000;
	uint32_t base;
	uint16_t high_count, low_count, rcv_count, xmit_count;
	struct device *dev = i2c->dev;

	if (speed > 540000) {
	dev_warn(dev, "Speed too high (%d Hz), using 540 kHz\n", speed);
	speed = 540000;
	} else if (speed < 12000) {
	dev_warn(dev, "Speed too low (%d Hz), using 12 kHz\n", speed);
	speed = 12000;
	}

	/*
	* The timing derivation algorithm. There is no documentation for this
	* algorithm available, it was derived by using the scope and fiddling
	* with constants until the result observed on the scope was good enough
	* for 20kHz, 50kHz, 100kHz, 200kHz, 300kHz and 400kHz. It should be
	* possible to assume the algorithm works for other frequencies as well.
	*
	* Note it was necessary to cap the frequency on both ends as it's not
	* possible to configure completely arbitrary frequency for the I2C bus
	* clock.
	*/
	base = ((clk / speed) - 38) / 2;
	high_count = base + 3;
	low_count = base - 3;
	rcv_count = (high_count * 3) / 4;
	xmit_count = low_count / 4;

	i2c->timing0 = (high_count << 16) \| rcv_count;
	i2c->timing1 = (low_count << 16) \| xmit_count;
	}

	static int mxs_i2c_get_ofdata(struct mxs_i2c_dev *i2c)
	{
	uint32_t speed;
	struct device *dev = i2c->dev;
	struct device_node *node = dev->of_node;
	int ret;

	ret = of_property_read_u32(node, "clock-frequency", &speed);
	if (ret) {
	dev_warn(dev, "No I2C speed selected, using 100kHz\n");
	speed = 100000;
	}

	mxs_i2c_derive_timing(i2c, speed);

	return 0;
	}

	static int mxs_i2c_probe(struct platform_device *pdev)
	{
	struct device *dev = &pdev->dev;
	struct mxs_i2c_dev *i2c;
	struct i2c_adapter *adap;
	struct pinctrl *pinctrl;
	struct resource *res;
	resource_size_t res_size;
	int err, irq;

	pinctrl = devm_pinctrl_get_select_default(dev);
	if (IS_ERR(pinctrl))
	return PTR_ERR(pinctrl);

	i2c = devm_kzalloc(dev, sizeof(struct mxs_i2c_dev), GFP_KERNEL);
	if (!i2c)
	return -ENOMEM;

	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
	irq = platform_get_irq(pdev, 0);

	if (!res \|\| irq < 0)
	return -ENOENT;

	res_size = resource_size(res);
	if (!devm_request_mem_region(dev, res->start, res_size, res->name))
	return -EBUSY;

	i2c->regs = devm_ioremap_nocache(dev, res->start, res_size);
	if (!i2c->regs)
	return -EBUSY;

	err = devm_request_irq(dev, irq, mxs_i2c_isr, 0, dev_name(dev), i2c);
	if (err)
	return err;

	i2c->dev = dev;

	init_completion(&i2c->cmd_complete);

	if (dev->of_node) {
	err = mxs_i2c_get_ofdata(i2c);
	if (err)
	return err;
	}

	/* Setup the DMA */
	i2c->dmach = dma_request_slave_channel(dev, "rx-tx");
	if (!i2c->dmach) {
	dev_err(dev, "Failed to request dma\n");
	return -ENODEV;
	}

	platform_set_drvdata(pdev, i2c);

	/* Do reset to enforce correct startup after pinmuxing */
	mxs_i2c_reset(i2c);

	adap = &i2c->adapter;
	strlcpy(adap->name, "MXS I2C adapter", sizeof(adap->name));
	adap->owner = THIS_MODULE;
	adap->algo = &mxs_i2c_algo;
	adap->dev.parent = dev;
	adap->nr = pdev->id;
	adap->dev.of_node = pdev->dev.of_node;
	i2c_set_adapdata(adap, i2c);
	err = i2c_add_numbered_adapter(adap);
	if (err) {
	dev_err(dev, "Failed to add adapter (%d)\n", err);
	writel(MXS_I2C_CTRL0_SFTRST,
	i2c->regs + MXS_I2C_CTRL0_SET);
	return err;
	}

	of_i2c_register_devices(adap);

	return 0;
	}

	static int mxs_i2c_remove(struct platform_device *pdev)
	{
	struct mxs_i2c_dev *i2c = platform_get_drvdata(pdev);

	i2c_del_adapter(&i2c->adapter);

	if (i2c->dmach)
	dma_release_channel(i2c->dmach);

	writel(MXS_I2C_CTRL0_SFTRST, i2c->regs + MXS_I2C_CTRL0_SET);

	return 0;
	}

	static const struct of_device_id mxs_i2c_dt_ids[] = {
	{ .compatible = "fsl,imx28-i2c", },
	{ /* sentinel */ }
	};
	MODULE_DEVICE_TABLE(of, mxs_i2c_dt_ids);

	static struct platform_driver mxs_i2c_driver = {
	.driver = {
	.name = DRIVER_NAME,
	.owner = THIS_MODULE,
	.of_match_table = mxs_i2c_dt_ids,
	},
	.remove = mxs_i2c_remove,
	};

	static int __init mxs_i2c_init(void)
	{
	return platform_driver_probe(&mxs_i2c_driver, mxs_i2c_probe);
	}
	subsys_initcall(mxs_i2c_init);

	static void __exit mxs_i2c_exit(void)
	{
	platform_driver_unregister(&mxs_i2c_driver);
	}
	module_exit(mxs_i2c_exit);

	MODULE_AUTHOR("Wolfram Sang <w.sang@pengutronix.de>");
	MODULE_DESCRIPTION("MXS I2C Bus Driver");
	MODULE_LICENSE("GPL");
	MODULE_ALIAS("platform:" DRIVER_NAME);