x86/xen: resume timer irqs early

[linux/fpc-iii.git] / drivers / i2c / busses / i2c-mxs.c

/*
 * 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/stmp_device.h>
#include <linux/of.h>
#include <linux/of_device.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;
        uint32_t timing2;

        /* 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 int mxs_i2c_reset(struct mxs_i2c_dev *i2c)
{
        int ret = stmp_reset_block(i2c->regs);
        if (ret)
                return ret;

        /*
         * 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(i2c->timing2, i2c->regs + MXS_I2C_TIMING2);

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

        return 0;
}

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, err;
        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) {
                        err = mxs_i2c_reset(i2c);
                        if (err)
                                return err;
                }
        } 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);
        ret = mxs_i2c_reset(i2c);
        if (ret)
                return ret;

        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, uint32_t speed)
{
        /* The I2C block clock runs at 24MHz */
        const uint32_t clk = 24000000;
        uint32_t divider;
        uint16_t high_count, low_count, rcv_count, xmit_count;
        uint32_t bus_free, leadin;
        struct device *dev = i2c->dev;

        divider = DIV_ROUND_UP(clk, speed);

        if (divider < 25) {
                /*
                 * limit the divider, so that min(low_count, high_count)
                 * is >= 1
                 */
                divider = 25;
                dev_warn(dev,
                        "Speed too high (%u.%03u kHz), using %u.%03u kHz\n",
                        speed / 1000, speed % 1000,
                        clk / divider / 1000, clk / divider % 1000);
        } else if (divider > 1897) {
                /*
                 * limit the divider, so that max(low_count, high_count)
                 * cannot exceed 1023
                 */
                divider = 1897;
                dev_warn(dev,
                        "Speed too low (%u.%03u kHz), using %u.%03u kHz\n",
                        speed / 1000, speed % 1000,
                        clk / divider / 1000, clk / divider % 1000);
        }

        /*
         * The I2C spec specifies the following timing data:
         *                          standard mode  fast mode Bitfield name
         * tLOW (SCL LOW period)     4700 ns        1300 ns
         * tHIGH (SCL HIGH period)   4000 ns         600 ns
         * tSU;DAT (data setup time)  250 ns         100 ns
         * tHD;STA (START hold time) 4000 ns         600 ns
         * tBUF (bus free time)      4700 ns        1300 ns
         *
         * The hardware (of the i.MX28 at least) seems to add 2 additional
         * clock cycles to the low_count and 7 cycles to the high_count.
         * This is compensated for by subtracting the respective constants
         * from the values written to the timing registers.
         */
        if (speed > 100000) {
                /* fast mode */
                low_count = DIV_ROUND_CLOSEST(divider * 13, (13 + 6));
                high_count = DIV_ROUND_CLOSEST(divider * 6, (13 + 6));
                leadin = DIV_ROUND_UP(600 * (clk / 1000000), 1000);
                bus_free = DIV_ROUND_UP(1300 * (clk / 1000000), 1000);
        } else {
                /* normal mode */
                low_count = DIV_ROUND_CLOSEST(divider * 47, (47 + 40));
                high_count = DIV_ROUND_CLOSEST(divider * 40, (47 + 40));
                leadin = DIV_ROUND_UP(4700 * (clk / 1000000), 1000);
                bus_free = DIV_ROUND_UP(4700 * (clk / 1000000), 1000);
        }
        rcv_count = high_count * 3 / 8;
        xmit_count = low_count * 3 / 8;

        dev_dbg(dev,
                "speed=%u(actual %u) divider=%u low=%u high=%u xmit=%u rcv=%u leadin=%u bus_free=%u\n",
                speed, clk / divider, divider, low_count, high_count,
                xmit_count, rcv_count, leadin, bus_free);

        low_count -= 2;
        high_count -= 7;
        i2c->timing0 = (high_count << 16) | rcv_count;
        i2c->timing1 = (low_count << 16) | xmit_count;
        i2c->timing2 = (bus_free << 16 | leadin);
}

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 resource *res;
        resource_size_t res_size;
        int err, irq;

        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 */
        err = mxs_i2c_reset(i2c);
        if (err)
                return err;

        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;
        }

        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,
                   },
        .probe = mxs_i2c_probe,
        .remove = mxs_i2c_remove,
};

static int __init mxs_i2c_init(void)
{
        return platform_driver_register(&mxs_i2c_driver);
}
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);