// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright (C) 2007-2012 ST-Ericsson AB
 * ST DDC I2C master mode driver, used in e.g. U300 series platforms.
 * Author: Linus Walleij <linus.walleij@stericsson.com>
 * Author: Jonas Aaberg <jonas.aberg@stericsson.com>
 */
#include <linux/init.h>
#include <linux/module.h>
#include <linux/platform_device.h>
#include <linux/delay.h>
#include <linux/i2c.h>
#include <linux/spinlock.h>
#include <linux/completion.h>
#include <linux/err.h>
#include <linux/interrupt.h>
#include <linux/clk.h>
#include <linux/io.h>
#include <linux/slab.h>

/* the name of this kernel module */
#define NAME "stu300"

/* CR (Control Register) 8bit (R/W) */
#define I2C_CR                                  (0x00000000)
#define I2C_CR_RESET_VALUE                      (0x00)
#define I2C_CR_RESET_UMASK                      (0x00)
#define I2C_CR_DDC1_ENABLE                      (0x80)
#define I2C_CR_TRANS_ENABLE                     (0x40)
#define I2C_CR_PERIPHERAL_ENABLE                (0x20)
#define I2C_CR_DDC2B_ENABLE                     (0x10)
#define I2C_CR_START_ENABLE                     (0x08)
#define I2C_CR_ACK_ENABLE                       (0x04)
#define I2C_CR_STOP_ENABLE                      (0x02)
#define I2C_CR_INTERRUPT_ENABLE                 (0x01)
/* SR1 (Status Register 1) 8bit (R/-) */
#define I2C_SR1                                 (0x00000004)
#define I2C_SR1_RESET_VALUE                     (0x00)
#define I2C_SR1_RESET_UMASK                     (0x00)
#define I2C_SR1_EVF_IND                         (0x80)
#define I2C_SR1_ADD10_IND                       (0x40)
#define I2C_SR1_TRA_IND                         (0x20)
#define I2C_SR1_BUSY_IND                        (0x10)
#define I2C_SR1_BTF_IND                         (0x08)
#define I2C_SR1_ADSL_IND                        (0x04)
#define I2C_SR1_MSL_IND                         (0x02)
#define I2C_SR1_SB_IND                          (0x01)
/* SR2 (Status Register 2) 8bit (R/-) */
#define I2C_SR2                                 (0x00000008)
#define I2C_SR2_RESET_VALUE                     (0x00)
#define I2C_SR2_RESET_UMASK                     (0x40)
#define I2C_SR2_MASK                            (0xBF)
#define I2C_SR2_SCLFAL_IND                      (0x80)
#define I2C_SR2_ENDAD_IND                       (0x20)
#define I2C_SR2_AF_IND                          (0x10)
#define I2C_SR2_STOPF_IND                       (0x08)
#define I2C_SR2_ARLO_IND                        (0x04)
#define I2C_SR2_BERR_IND                        (0x02)
#define I2C_SR2_DDC2BF_IND                      (0x01)
/* CCR (Clock Control Register) 8bit (R/W) */
#define I2C_CCR                                 (0x0000000C)
#define I2C_CCR_RESET_VALUE                     (0x00)
#define I2C_CCR_RESET_UMASK                     (0x00)
#define I2C_CCR_MASK                            (0xFF)
#define I2C_CCR_FMSM                            (0x80)
#define I2C_CCR_CC_MASK                         (0x7F)
/* OAR1 (Own Address Register 1) 8bit (R/W) */
#define I2C_OAR1                                (0x00000010)
#define I2C_OAR1_RESET_VALUE                    (0x00)
#define I2C_OAR1_RESET_UMASK                    (0x00)
#define I2C_OAR1_ADD_MASK                       (0xFF)
/* OAR2 (Own Address Register 2) 8bit (R/W) */
#define I2C_OAR2                                (0x00000014)
#define I2C_OAR2_RESET_VALUE                    (0x40)
#define I2C_OAR2_RESET_UMASK                    (0x19)
#define I2C_OAR2_MASK                           (0xE6)
#define I2C_OAR2_FR_25_10MHZ                    (0x00)
#define I2C_OAR2_FR_10_1667MHZ                  (0x20)
#define I2C_OAR2_FR_1667_2667MHZ                (0x40)
#define I2C_OAR2_FR_2667_40MHZ                  (0x60)
#define I2C_OAR2_FR_40_5333MHZ                  (0x80)
#define I2C_OAR2_FR_5333_66MHZ                  (0xA0)
#define I2C_OAR2_FR_66_80MHZ                    (0xC0)
#define I2C_OAR2_FR_80_100MHZ                   (0xE0)
#define I2C_OAR2_FR_MASK                        (0xE0)
#define I2C_OAR2_ADD_MASK                       (0x06)
/* DR (Data Register) 8bit (R/W) */
#define I2C_DR                                  (0x00000018)
#define I2C_DR_RESET_VALUE                      (0x00)
#define I2C_DR_RESET_UMASK                      (0xFF)
#define I2C_DR_D_MASK                           (0xFF)
/* ECCR (Extended Clock Control Register) 8bit (R/W) */
#define I2C_ECCR                                (0x0000001C)
#define I2C_ECCR_RESET_VALUE                    (0x00)
#define I2C_ECCR_RESET_UMASK                    (0xE0)
#define I2C_ECCR_MASK                           (0x1F)
#define I2C_ECCR_CC_MASK                        (0x1F)

/*
 * These events are more or less responses to commands
 * sent into the hardware, presumably reflecting the state
 * of an internal state machine.
 */
enum stu300_event {
        STU300_EVENT_NONE = 0,
        STU300_EVENT_1,
        STU300_EVENT_2,
        STU300_EVENT_3,
        STU300_EVENT_4,
        STU300_EVENT_5,
        STU300_EVENT_6,
        STU300_EVENT_7,
        STU300_EVENT_8,
        STU300_EVENT_9
};

enum stu300_error {
        STU300_ERROR_NONE = 0,
        STU300_ERROR_ACKNOWLEDGE_FAILURE,
        STU300_ERROR_BUS_ERROR,
        STU300_ERROR_ARBITRATION_LOST,
        STU300_ERROR_UNKNOWN
};

/* timeout waiting for the controller to respond */
#define STU300_TIMEOUT (msecs_to_jiffies(1000))

/*
 * The number of address send athemps tried before giving up.
 * If the first one fails it seems like 5 to 8 attempts are required.
 */
#define NUM_ADDR_RESEND_ATTEMPTS 12

/* I2C clock speed, in Hz 0-400kHz*/
static unsigned int scl_frequency = 100000;
module_param(scl_frequency, uint,  0644);

/**
 * struct stu300_dev - the stu300 driver state holder
 * @pdev: parent platform device
 * @adapter: corresponding I2C adapter
 * @clk: hardware block clock
 * @irq: assigned interrupt line
 * @cmd_issue_lock: this locks the following cmd_ variables
 * @cmd_complete: acknowledge completion for an I2C command
 * @cmd_event: expected event coming in as a response to a command
 * @cmd_err: error code as response to a command
 * @speed: current bus speed in Hz
 * @msg_index: index of current message
 * @msg_len: length of current message
 */

struct stu300_dev {
        struct platform_device  *pdev;
        struct i2c_adapter      adapter;
        void __iomem            *virtbase;
        struct clk              *clk;
        int                     irq;
        spinlock_t              cmd_issue_lock;
        struct completion       cmd_complete;
        enum stu300_event       cmd_event;
        enum stu300_error       cmd_err;
        unsigned int            speed;
        int                     msg_index;
        int                     msg_len;
};

/* Local forward function declarations */
static int stu300_init_hw(struct stu300_dev *dev);

/*
 * The block needs writes in both MSW and LSW in order
 * for all data lines to reach their destination.
 */
static inline void stu300_wr8(u32 value, void __iomem *address)
{
        writel((value << 16) | value, address);
}

/*
 * This merely masks off the duplicates which appear
 * in bytes 1-3. You _MUST_ use 32-bit bus access on this
 * device, else it will not work.
 */
static inline u32 stu300_r8(void __iomem *address)
{
        return readl(address) & 0x000000FFU;
}

static void stu300_irq_enable(struct stu300_dev *dev)
{
        u32 val;
        val = stu300_r8(dev->virtbase + I2C_CR);
        val |= I2C_CR_INTERRUPT_ENABLE;
        /* Twice paranoia (possible HW glitch) */
        stu300_wr8(val, dev->virtbase + I2C_CR);
        stu300_wr8(val, dev->virtbase + I2C_CR);
}

static void stu300_irq_disable(struct stu300_dev *dev)
{
        u32 val;
        val = stu300_r8(dev->virtbase + I2C_CR);
        val &= ~I2C_CR_INTERRUPT_ENABLE;
        /* Twice paranoia (possible HW glitch) */
        stu300_wr8(val, dev->virtbase + I2C_CR);
        stu300_wr8(val, dev->virtbase + I2C_CR);
}


/*
 * Tells whether a certain event or events occurred in
 * response to a command. The events represent states in
 * the internal state machine of the hardware. The events
 * are not very well described in the hardware
 * documentation and can only be treated as abstract state
 * machine states.
 *
 * @ret 0 = event has not occurred or unknown error, any
 * other value means the correct event occurred or an error.
 */

static int stu300_event_occurred(struct stu300_dev *dev,
                                   enum stu300_event mr_event) {
        u32 status1;
        u32 status2;

        /* What event happened? */
        status1 = stu300_r8(dev->virtbase + I2C_SR1);

        if (!(status1 & I2C_SR1_EVF_IND))
                /* No event at all */
                return 0;

        status2 = stu300_r8(dev->virtbase + I2C_SR2);

        /* Block any multiple interrupts */
        stu300_irq_disable(dev);

        /* Check for errors first */
        if (status2 & I2C_SR2_AF_IND) {
                dev->cmd_err = STU300_ERROR_ACKNOWLEDGE_FAILURE;
                return 1;
        } else if (status2 & I2C_SR2_BERR_IND) {
                dev->cmd_err = STU300_ERROR_BUS_ERROR;
                return 1;
        } else if (status2 & I2C_SR2_ARLO_IND) {
                dev->cmd_err = STU300_ERROR_ARBITRATION_LOST;
                return 1;
        }

        switch (mr_event) {
        case STU300_EVENT_1:
                if (status1 & I2C_SR1_ADSL_IND)
                        return 1;
                break;
        case STU300_EVENT_2:
        case STU300_EVENT_3:
        case STU300_EVENT_7:
        case STU300_EVENT_8:
                if (status1 & I2C_SR1_BTF_IND) {
                        return 1;
                }
                break;
        case STU300_EVENT_4:
                if (status2 & I2C_SR2_STOPF_IND)
                        return 1;
                break;
        case STU300_EVENT_5:
                if (status1 & I2C_SR1_SB_IND)
                        /* Clear start bit */
                        return 1;
                break;
        case STU300_EVENT_6:
                if (status2 & I2C_SR2_ENDAD_IND) {
                        /* First check for any errors */
                        return 1;
                }
                break;
        case STU300_EVENT_9:
                if (status1 & I2C_SR1_ADD10_IND)
                        return 1;
                break;
        default:
                break;
        }
        /* If we get here, we're on thin ice.
         * Here we are in a status where we have
         * gotten a response that does not match
         * what we requested.
         */
        dev->cmd_err = STU300_ERROR_UNKNOWN;
        dev_err(&dev->pdev->dev,
                "Unhandled interrupt! %d sr1: 0x%x sr2: 0x%x\n",
                mr_event, status1, status2);
        return 0;
}

static irqreturn_t stu300_irh(int irq, void *data)
{
        struct stu300_dev *dev = data;
        int res;

        /* Just make sure that the block is clocked */
        clk_enable(dev->clk);

        /* See if this was what we were waiting for */
        spin_lock(&dev->cmd_issue_lock);

        res = stu300_event_occurred(dev, dev->cmd_event);
        if (res || dev->cmd_err != STU300_ERROR_NONE)
                complete(&dev->cmd_complete);

        spin_unlock(&dev->cmd_issue_lock);

        clk_disable(dev->clk);

        return IRQ_HANDLED;
}

/*
 * Sends a command and then waits for the bits masked by *flagmask*
 * to go high or low by IRQ awaiting.
 */
static int stu300_start_and_await_event(struct stu300_dev *dev,
                                          u8 cr_value,
                                          enum stu300_event mr_event)
{
        int ret;

        /* Lock command issue, fill in an event we wait for */
        spin_lock_irq(&dev->cmd_issue_lock);
        init_completion(&dev->cmd_complete);
        dev->cmd_err = STU300_ERROR_NONE;
        dev->cmd_event = mr_event;
        spin_unlock_irq(&dev->cmd_issue_lock);

        /* Turn on interrupt, send command and wait. */
        cr_value |= I2C_CR_INTERRUPT_ENABLE;
        stu300_wr8(cr_value, dev->virtbase + I2C_CR);
        ret = wait_for_completion_interruptible_timeout(&dev->cmd_complete,
                                                        STU300_TIMEOUT);
        if (ret < 0) {
                dev_err(&dev->pdev->dev,
                       "wait_for_completion_interruptible_timeout() "
                       "returned %d waiting for event %04x\n", ret, mr_event);
                return ret;
        }

        if (ret == 0) {
                dev_err(&dev->pdev->dev, "controller timed out "
                       "waiting for event %d, reinit hardware\n", mr_event);
                (void) stu300_init_hw(dev);
                return -ETIMEDOUT;
        }

        if (dev->cmd_err != STU300_ERROR_NONE) {
                dev_err(&dev->pdev->dev, "controller (start) "
                       "error %d waiting for event %d, reinit hardware\n",
                       dev->cmd_err, mr_event);
                (void) stu300_init_hw(dev);
                return -EIO;
        }

        return 0;
}

/*
 * This waits for a flag to be set, if it is not set on entry, an interrupt is
 * configured to wait for the flag using a completion.
 */
static int stu300_await_event(struct stu300_dev *dev,
                                enum stu300_event mr_event)
{
        int ret;

        /* Is it already here? */
        spin_lock_irq(&dev->cmd_issue_lock);
        dev->cmd_err = STU300_ERROR_NONE;
        dev->cmd_event = mr_event;

        init_completion(&dev->cmd_complete);

        /* Turn on the I2C interrupt for current operation */
        stu300_irq_enable(dev);

        /* Unlock the command block and wait for the event to occur */
        spin_unlock_irq(&dev->cmd_issue_lock);

        ret = wait_for_completion_interruptible_timeout(&dev->cmd_complete,
                                                        STU300_TIMEOUT);
        if (ret < 0) {
                dev_err(&dev->pdev->dev,
                       "wait_for_completion_interruptible_timeout()"
                       "returned %d waiting for event %04x\n", ret, mr_event);
                return ret;
        }

        if (ret == 0) {
                if (mr_event != STU300_EVENT_6) {
                        dev_err(&dev->pdev->dev, "controller "
                                "timed out waiting for event %d, reinit "
                                "hardware\n", mr_event);
                        (void) stu300_init_hw(dev);
                }
                return -ETIMEDOUT;
        }

        if (dev->cmd_err != STU300_ERROR_NONE) {
                if (mr_event != STU300_EVENT_6) {
                        dev_err(&dev->pdev->dev, "controller "
                                "error (await_event) %d waiting for event %d, "
                               "reinit hardware\n", dev->cmd_err, mr_event);
                        (void) stu300_init_hw(dev);
                }
                return -EIO;
        }

        return 0;
}

/*
 * Waits for the busy bit to go low by repeated polling.
 */
#define BUSY_RELEASE_ATTEMPTS 10
static int stu300_wait_while_busy(struct stu300_dev *dev)
{
        unsigned long timeout;
        int i;

        for (i = 0; i < BUSY_RELEASE_ATTEMPTS; i++) {
                timeout = jiffies + STU300_TIMEOUT;

                while (!time_after(jiffies, timeout)) {
                        /* Is not busy? */
                        if ((stu300_r8(dev->virtbase + I2C_SR1) &
                             I2C_SR1_BUSY_IND) == 0)
                                return 0;
                        msleep(1);
                }

                dev_err(&dev->pdev->dev, "transaction timed out "
                        "waiting for device to be free (not busy). "
                       "Attempt: %d\n", i+1);

                dev_err(&dev->pdev->dev, "base address = "
                        "0x%08x, reinit hardware\n", (u32) dev->virtbase);

                (void) stu300_init_hw(dev);
        }

        dev_err(&dev->pdev->dev, "giving up after %d attempts "
                "to reset the bus.\n",  BUSY_RELEASE_ATTEMPTS);

        return -ETIMEDOUT;
}

struct stu300_clkset {
        unsigned long rate;
        u32 setting;
};

static const struct stu300_clkset stu300_clktable[] = {
        { 0,         0xFFU },
        { 2500000,   I2C_OAR2_FR_25_10MHZ },
        { 10000000,  I2C_OAR2_FR_10_1667MHZ },
        { 16670000,  I2C_OAR2_FR_1667_2667MHZ },
        { 26670000,  I2C_OAR2_FR_2667_40MHZ },
        { 40000000,  I2C_OAR2_FR_40_5333MHZ },
        { 53330000,  I2C_OAR2_FR_5333_66MHZ },
        { 66000000,  I2C_OAR2_FR_66_80MHZ },
        { 80000000,  I2C_OAR2_FR_80_100MHZ },
        { 100000000, 0xFFU },
};


static int stu300_set_clk(struct stu300_dev *dev, unsigned long clkrate)
{

        u32 val;
        int i = 0;

        /* Locate the appropriate clock setting */
        while (i < ARRAY_SIZE(stu300_clktable) - 1 &&
               stu300_clktable[i].rate < clkrate)
                i++;

        if (stu300_clktable[i].setting == 0xFFU) {
                dev_err(&dev->pdev->dev, "too %s clock rate requested "
                        "(%lu Hz).\n", i ? "high" : "low", clkrate);
                return -EINVAL;
        }

        stu300_wr8(stu300_clktable[i].setting,
                   dev->virtbase + I2C_OAR2);

        dev_dbg(&dev->pdev->dev, "Clock rate %lu Hz, I2C bus speed %d Hz "
                "virtbase %p\n", clkrate, dev->speed, dev->virtbase);

        if (dev->speed > 100000)
                /* Fast Mode I2C */
                val = ((clkrate/dev->speed) - 9)/3 + 1;
        else
                /* Standard Mode I2C */
                val = ((clkrate/dev->speed) - 7)/2 + 1;

        /* According to spec the divider must be > 2 */
        if (val < 0x002) {
                dev_err(&dev->pdev->dev, "too low clock rate (%lu Hz).\n",
                        clkrate);
                return -EINVAL;
        }

        /* We have 12 bits clock divider only! */
        if (val & 0xFFFFF000U) {
                dev_err(&dev->pdev->dev, "too high clock rate (%lu Hz).\n",
                        clkrate);
                return -EINVAL;
        }

        if (dev->speed > 100000) {
                /* CC6..CC0 */
                stu300_wr8((val & I2C_CCR_CC_MASK) | I2C_CCR_FMSM,
                           dev->virtbase + I2C_CCR);
                dev_dbg(&dev->pdev->dev, "set clock divider to 0x%08x, "
                        "Fast Mode I2C\n", val);
        } else {
                /* CC6..CC0 */
                stu300_wr8((val & I2C_CCR_CC_MASK),
                           dev->virtbase + I2C_CCR);
                dev_dbg(&dev->pdev->dev, "set clock divider to "
                        "0x%08x, Standard Mode I2C\n", val);
        }

        /* CC11..CC7 */
        stu300_wr8(((val >> 7) & 0x1F),
                   dev->virtbase + I2C_ECCR);

        return 0;
}


static int stu300_init_hw(struct stu300_dev *dev)
{
        u32 dummy;
        unsigned long clkrate;
        int ret;

        /* Disable controller */
        stu300_wr8(0x00, dev->virtbase + I2C_CR);
        /*
         * Set own address to some default value (0x00).
         * We do not support slave mode anyway.
         */
        stu300_wr8(0x00, dev->virtbase + I2C_OAR1);
        /*
         * The I2C controller only operates properly in 26 MHz but we
         * program this driver as if we didn't know. This will also set the two
         * high bits of the own address to zero as well.
         * There is no known hardware issue with running in 13 MHz
         * However, speeds over 200 kHz are not used.
         */
        clkrate = clk_get_rate(dev->clk);
        ret = stu300_set_clk(dev, clkrate);

        if (ret)
                return ret;
        /*
         * Enable block, do it TWICE (hardware glitch)
         * Setting bit 7 can enable DDC mode. (Not used currently.)
         */
        stu300_wr8(I2C_CR_PERIPHERAL_ENABLE,
                                  dev->virtbase + I2C_CR);
        stu300_wr8(I2C_CR_PERIPHERAL_ENABLE,
                                  dev->virtbase + I2C_CR);
        /* Make a dummy read of the status register SR1 & SR2 */
        dummy = stu300_r8(dev->virtbase + I2C_SR2);
        dummy = stu300_r8(dev->virtbase + I2C_SR1);

        return 0;
}



/* Send slave address. */
static int stu300_send_address(struct stu300_dev *dev,
                                 struct i2c_msg *msg, int resend)
{
        u32 val;
        int ret;

        if (msg->flags & I2C_M_TEN) {
                /* This is probably how 10 bit addresses look */
                val = (0xf0 | (((u32) msg->addr & 0x300) >> 7)) &
                        I2C_DR_D_MASK;
                if (msg->flags & I2C_M_RD)
                        /* This is the direction bit */
                        val |= 0x01;
        } else {
                val = i2c_8bit_addr_from_msg(msg);
        }

        if (resend) {
                if (msg->flags & I2C_M_RD)
                        dev_dbg(&dev->pdev->dev, "read resend\n");
                else
                        dev_dbg(&dev->pdev->dev, "write resend\n");
        }

        stu300_wr8(val, dev->virtbase + I2C_DR);

        /* For 10bit addressing, await 10bit request (EVENT 9) */
        if (msg->flags & I2C_M_TEN) {
                ret = stu300_await_event(dev, STU300_EVENT_9);
                /*
                 * The slave device wants a 10bit address, send the rest
                 * of the bits (the LSBits)
                 */
                val = msg->addr & I2C_DR_D_MASK;
                /* This clears "event 9" */
                stu300_wr8(val, dev->virtbase + I2C_DR);
                if (ret != 0)
                        return ret;
        }
        /* FIXME: Why no else here? two events for 10bit?
         * Await event 6 (normal) or event 9 (10bit)
         */

        if (resend)
                dev_dbg(&dev->pdev->dev, "await event 6\n");
        ret = stu300_await_event(dev, STU300_EVENT_6);

        /*
         * Clear any pending EVENT 6 no matter what happened during
         * await_event.
         */
        val = stu300_r8(dev->virtbase + I2C_CR);
        val |= I2C_CR_PERIPHERAL_ENABLE;
        stu300_wr8(val, dev->virtbase + I2C_CR);

        return ret;
}

static int stu300_xfer_msg(struct i2c_adapter *adap,
                             struct i2c_msg *msg, int stop)
{
        u32 cr;
        u32 val;
        u32 i;
        int ret;
        int attempts = 0;
        struct stu300_dev *dev = i2c_get_adapdata(adap);

        clk_enable(dev->clk);

        /* Remove this if (0) to trace each and every message. */
        if (0) {
                dev_dbg(&dev->pdev->dev, "I2C message to: 0x%04x, len: %d, "
                        "flags: 0x%04x, stop: %d\n",
                        msg->addr, msg->len, msg->flags, stop);
        }

        /*
         * For some reason, sending the address sometimes fails when running
         * on  the 13 MHz clock. No interrupt arrives. This is a work around,
         * which tries to restart and send the address up to 10 times before
         * really giving up. Usually 5 to 8 attempts are enough.
         */
        do {
                if (attempts)
                        dev_dbg(&dev->pdev->dev, "wait while busy\n");
                /* Check that the bus is free, or wait until some timeout */
                ret = stu300_wait_while_busy(dev);
                if (ret != 0)
                        goto exit_disable;

                if (attempts)
                        dev_dbg(&dev->pdev->dev, "re-int hw\n");
                /*
                 * According to ST, there is no problem if the clock is
                 * changed between 13 and 26 MHz during a transfer.
                 */
                ret = stu300_init_hw(dev);
                if (ret)
                        goto exit_disable;

                /* Send a start condition */
                cr = I2C_CR_PERIPHERAL_ENABLE;
                /* Setting the START bit puts the block in master mode */
                if (!(msg->flags & I2C_M_NOSTART))
                        cr |= I2C_CR_START_ENABLE;
                if ((msg->flags & I2C_M_RD) && (msg->len > 1))
                        /* On read more than 1 byte, we need ack. */
                        cr |= I2C_CR_ACK_ENABLE;
                /* Check that it gets through */
                if (!(msg->flags & I2C_M_NOSTART)) {
                        if (attempts)
                                dev_dbg(&dev->pdev->dev, "send start event\n");
                        ret = stu300_start_and_await_event(dev, cr,
                                                             STU300_EVENT_5);
                }

                if (attempts)
                        dev_dbg(&dev->pdev->dev, "send address\n");

                if (ret == 0)
                        /* Send address */
                        ret = stu300_send_address(dev, msg, attempts != 0);

                if (ret != 0) {
                        attempts++;
                        dev_dbg(&dev->pdev->dev, "failed sending address, "
                                "retrying. Attempt: %d msg_index: %d/%d\n",
                               attempts, dev->msg_index, dev->msg_len);
                }

        } while (ret != 0 && attempts < NUM_ADDR_RESEND_ATTEMPTS);

        if (attempts < NUM_ADDR_RESEND_ATTEMPTS && attempts > 0) {
                dev_dbg(&dev->pdev->dev, "managed to get address "
                        "through after %d attempts\n", attempts);
        } else if (attempts == NUM_ADDR_RESEND_ATTEMPTS) {
                dev_dbg(&dev->pdev->dev, "I give up, tried %d times "
                        "to resend address.\n",
                        NUM_ADDR_RESEND_ATTEMPTS);
                goto exit_disable;
        }


        if (msg->flags & I2C_M_RD) {
                /* READ: we read the actual bytes one at a time */
                for (i = 0; i < msg->len; i++) {
                        if (i == msg->len-1) {
                                /*
                                 * Disable ACK and set STOP condition before
                                 * reading last byte
                                 */
                                val = I2C_CR_PERIPHERAL_ENABLE;

                                if (stop)
                                        val |= I2C_CR_STOP_ENABLE;

                                stu300_wr8(val,
                                           dev->virtbase + I2C_CR);
                        }
                        /* Wait for this byte... */
                        ret = stu300_await_event(dev, STU300_EVENT_7);
                        if (ret != 0)
                                goto exit_disable;
                        /* This clears event 7 */
                        msg->buf[i] = (u8) stu300_r8(dev->virtbase + I2C_DR);
                }
        } else {
                /* WRITE: we send the actual bytes one at a time */
                for (i = 0; i < msg->len; i++) {
                        /* Write the byte */
                        stu300_wr8(msg->buf[i],
                                   dev->virtbase + I2C_DR);
                        /* Check status */
                        ret = stu300_await_event(dev, STU300_EVENT_8);
                        /* Next write to DR will clear event 8 */
                        if (ret != 0) {
                                dev_err(&dev->pdev->dev, "error awaiting "
                                       "event 8 (%d)\n", ret);
                                goto exit_disable;
                        }
                }
                /* Check NAK */
                if (!(msg->flags & I2C_M_IGNORE_NAK)) {
                        if (stu300_r8(dev->virtbase + I2C_SR2) &
                            I2C_SR2_AF_IND) {
                                dev_err(&dev->pdev->dev, "I2C payload "
                                       "send returned NAK!\n");
                                ret = -EIO;
                                goto exit_disable;
                        }
                }
                if (stop) {
                        /* Send stop condition */
                        val = I2C_CR_PERIPHERAL_ENABLE;
                        val |= I2C_CR_STOP_ENABLE;
                        stu300_wr8(val, dev->virtbase + I2C_CR);
                }
        }

        /* Check that the bus is free, or wait until some timeout occurs */
        ret = stu300_wait_while_busy(dev);
        if (ret != 0) {
                dev_err(&dev->pdev->dev, "timeout waiting for transfer "
                       "to commence.\n");
                goto exit_disable;
        }

        /* Dummy read status registers */
        val = stu300_r8(dev->virtbase + I2C_SR2);
        val = stu300_r8(dev->virtbase + I2C_SR1);
        ret = 0;

 exit_disable:
        /* Disable controller */
        stu300_wr8(0x00, dev->virtbase + I2C_CR);
        clk_disable(dev->clk);
        return ret;
}

static int stu300_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs,
                         int num)
{
        int ret = -1;
        int i;

        struct stu300_dev *dev = i2c_get_adapdata(adap);
        dev->msg_len = num;

        for (i = 0; i < num; i++) {
                /*
                 * Another driver appears to send stop for each message,
                 * here we only do that for the last message. Possibly some
                 * peripherals require this behaviour, then their drivers
                 * have to send single messages in order to get "stop" for
                 * each message.
                 */
                dev->msg_index = i;

                ret = stu300_xfer_msg(adap, &msgs[i], (i == (num - 1)));

                if (ret != 0) {
                        num = ret;
                        break;
                }
        }

        return num;
}

static int stu300_xfer_todo(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
{
        /* TODO: implement polling for this case if need be. */
        WARN(1, "%s: atomic transfers not implemented\n", dev_name(&adap->dev));
        return -EOPNOTSUPP;
}

static u32 stu300_func(struct i2c_adapter *adap)
{
        /* This is the simplest thing you can think of... */
        return I2C_FUNC_I2C | I2C_FUNC_10BIT_ADDR;
}

static const struct i2c_algorithm stu300_algo = {
        .master_xfer = stu300_xfer,
        .master_xfer_atomic = stu300_xfer_todo,
        .functionality = stu300_func,
};

static const struct i2c_adapter_quirks stu300_quirks = {
        .flags = I2C_AQ_NO_ZERO_LEN,
};

static int stu300_probe(struct platform_device *pdev)
{
        struct stu300_dev *dev;
        struct i2c_adapter *adap;
        struct resource *res;
        int bus_nr;
        int ret = 0;

        dev = devm_kzalloc(&pdev->dev, sizeof(struct stu300_dev), GFP_KERNEL);
        if (!dev)
                return -ENOMEM;

        bus_nr = pdev->id;
        dev->clk = devm_clk_get(&pdev->dev, NULL);
        if (IS_ERR(dev->clk)) {
                dev_err(&pdev->dev, "could not retrieve i2c bus clock\n");
                return PTR_ERR(dev->clk);
        }

        dev->pdev = pdev;
        res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
        dev->virtbase = devm_ioremap_resource(&pdev->dev, res);
        dev_dbg(&pdev->dev, "initialize bus device I2C%d on virtual "
                "base %p\n", bus_nr, dev->virtbase);
        if (IS_ERR(dev->virtbase))
                return PTR_ERR(dev->virtbase);

        dev->irq = platform_get_irq(pdev, 0);
        ret = devm_request_irq(&pdev->dev, dev->irq, stu300_irh, 0, NAME, dev);
        if (ret < 0)
                return ret;

        dev->speed = scl_frequency;

        clk_prepare_enable(dev->clk);
        ret = stu300_init_hw(dev);
        clk_disable(dev->clk);
        if (ret != 0) {
                dev_err(&dev->pdev->dev, "error initializing hardware.\n");
                return -EIO;
        }

        /* IRQ event handling initialization */
        spin_lock_init(&dev->cmd_issue_lock);
        dev->cmd_event = STU300_EVENT_NONE;
        dev->cmd_err = STU300_ERROR_NONE;

        adap = &dev->adapter;
        adap->owner = THIS_MODULE;
        /* DDC class but actually often used for more generic I2C */
        adap->class = I2C_CLASS_DEPRECATED;
        strlcpy(adap->name, "ST Microelectronics DDC I2C adapter",
                sizeof(adap->name));
        adap->nr = bus_nr;
        adap->algo = &stu300_algo;
        adap->dev.parent = &pdev->dev;
        adap->dev.of_node = pdev->dev.of_node;
        adap->quirks = &stu300_quirks;

        i2c_set_adapdata(adap, dev);

        /* i2c device drivers may be active on return from add_adapter() */
        ret = i2c_add_numbered_adapter(adap);
        if (ret)
                return ret;

        platform_set_drvdata(pdev, dev);
        dev_info(&pdev->dev, "ST DDC I2C @ %p, irq %d\n",
                 dev->virtbase, dev->irq);

        return 0;
}

#ifdef CONFIG_PM_SLEEP
static int stu300_suspend(struct device *device)
{
        struct stu300_dev *dev = dev_get_drvdata(device);

        /* Turn off everything */
        stu300_wr8(0x00, dev->virtbase + I2C_CR);
        return 0;
}

static int stu300_resume(struct device *device)
{
        int ret = 0;
        struct stu300_dev *dev = dev_get_drvdata(device);

        clk_enable(dev->clk);
        ret = stu300_init_hw(dev);
        clk_disable(dev->clk);

        if (ret != 0)
                dev_err(device, "error re-initializing hardware.\n");
        return ret;
}

static SIMPLE_DEV_PM_OPS(stu300_pm, stu300_suspend, stu300_resume);
#define STU300_I2C_PM   (&stu300_pm)
#else
#define STU300_I2C_PM   NULL
#endif

static int stu300_remove(struct platform_device *pdev)
{
        struct stu300_dev *dev = platform_get_drvdata(pdev);

        i2c_del_adapter(&dev->adapter);
        /* Turn off everything */
        stu300_wr8(0x00, dev->virtbase + I2C_CR);
        return 0;
}

static const struct of_device_id stu300_dt_match[] = {
        { .compatible = "st,ddci2c" },
        {},
};
MODULE_DEVICE_TABLE(of, stu300_dt_match);

static struct platform_driver stu300_i2c_driver = {
        .driver = {
                .name   = NAME,
                .pm     = STU300_I2C_PM,
                .of_match_table = stu300_dt_match,
        },
        .probe = stu300_probe,
        .remove = stu300_remove,

};

static int __init stu300_init(void)
{
        return platform_driver_register(&stu300_i2c_driver);
}

static void __exit stu300_exit(void)
{
        platform_driver_unregister(&stu300_i2c_driver);
}

/*
 * The systems using this bus often have very basic devices such

 * as regulators on the I2C bus, so this needs to be loaded early.
 * Therefore it is registered in the subsys_initcall().
 */
subsys_initcall(stu300_init);
module_exit(stu300_exit);

MODULE_AUTHOR("Linus Walleij <linus.walleij@stericsson.com>");
MODULE_DESCRIPTION("ST Micro DDC I2C adapter (" NAME ")");
MODULE_LICENSE("GPL");
MODULE_ALIAS("platform:" NAME);