btrfs: add comments to barriers before waitqueue_active

[linux-2.6/btrfs-unstable.git] / drivers / i2c / busses / i2c-rk3x.c

/*
 * Driver for I2C adapter in Rockchip RK3xxx SoC
 *
 * Max Schwarz <max.schwarz@online.de>
 * based on the patches by Rockchip Inc.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/i2c.h>
#include <linux/interrupt.h>
#include <linux/errno.h>
#include <linux/err.h>
#include <linux/platform_device.h>
#include <linux/io.h>
#include <linux/of_address.h>
#include <linux/of_irq.h>
#include <linux/spinlock.h>
#include <linux/clk.h>
#include <linux/wait.h>
#include <linux/mfd/syscon.h>
#include <linux/regmap.h>
#include <linux/math64.h>


/* Register Map */
#define REG_CON        0x00 /* control register */
#define REG_CLKDIV     0x04 /* clock divisor register */
#define REG_MRXADDR    0x08 /* slave address for REGISTER_TX */
#define REG_MRXRADDR   0x0c /* slave register address for REGISTER_TX */
#define REG_MTXCNT     0x10 /* number of bytes to be transmitted */
#define REG_MRXCNT     0x14 /* number of bytes to be received */
#define REG_IEN        0x18 /* interrupt enable */
#define REG_IPD        0x1c /* interrupt pending */
#define REG_FCNT       0x20 /* finished count */

/* Data buffer offsets */
#define TXBUFFER_BASE 0x100
#define RXBUFFER_BASE 0x200

/* REG_CON bits */
#define REG_CON_EN        BIT(0)
enum {
        REG_CON_MOD_TX = 0,      /* transmit data */
        REG_CON_MOD_REGISTER_TX, /* select register and restart */
        REG_CON_MOD_RX,          /* receive data */
        REG_CON_MOD_REGISTER_RX, /* broken: transmits read addr AND writes
                                  * register addr */
};
#define REG_CON_MOD(mod)  ((mod) << 1)
#define REG_CON_MOD_MASK  (BIT(1) | BIT(2))
#define REG_CON_START     BIT(3)
#define REG_CON_STOP      BIT(4)
#define REG_CON_LASTACK   BIT(5) /* 1: send NACK after last received byte */
#define REG_CON_ACTACK    BIT(6) /* 1: stop if NACK is received */

/* REG_MRXADDR bits */
#define REG_MRXADDR_VALID(x) BIT(24 + (x)) /* [x*8+7:x*8] of MRX[R]ADDR valid */

/* REG_IEN/REG_IPD bits */
#define REG_INT_BTF       BIT(0) /* a byte was transmitted */
#define REG_INT_BRF       BIT(1) /* a byte was received */
#define REG_INT_MBTF      BIT(2) /* master data transmit finished */
#define REG_INT_MBRF      BIT(3) /* master data receive finished */
#define REG_INT_START     BIT(4) /* START condition generated */
#define REG_INT_STOP      BIT(5) /* STOP condition generated */
#define REG_INT_NAKRCV    BIT(6) /* NACK received */
#define REG_INT_ALL       0x7f

/* Constants */
#define WAIT_TIMEOUT      1000 /* ms */
#define DEFAULT_SCL_RATE  (100 * 1000) /* Hz */

enum rk3x_i2c_state {
        STATE_IDLE,
        STATE_START,
        STATE_READ,
        STATE_WRITE,
        STATE_STOP
};

/**
 * @grf_offset: offset inside the grf regmap for setting the i2c type
 */
struct rk3x_i2c_soc_data {
        int grf_offset;
};

struct rk3x_i2c {
        struct i2c_adapter adap;
        struct device *dev;
        struct rk3x_i2c_soc_data *soc_data;

        /* Hardware resources */
        void __iomem *regs;
        struct clk *clk;
        struct notifier_block clk_rate_nb;

        /* Settings */
        unsigned int scl_frequency;
        unsigned int scl_rise_ns;
        unsigned int scl_fall_ns;
        unsigned int sda_fall_ns;

        /* Synchronization & notification */
        spinlock_t lock;
        wait_queue_head_t wait;
        bool busy;

        /* Current message */
        struct i2c_msg *msg;
        u8 addr;
        unsigned int mode;
        bool is_last_msg;

        /* I2C state machine */
        enum rk3x_i2c_state state;
        unsigned int processed; /* sent/received bytes */
        int error;
};

static inline void i2c_writel(struct rk3x_i2c *i2c, u32 value,
                              unsigned int offset)
{
        writel(value, i2c->regs + offset);
}

static inline u32 i2c_readl(struct rk3x_i2c *i2c, unsigned int offset)
{
        return readl(i2c->regs + offset);
}

/* Reset all interrupt pending bits */
static inline void rk3x_i2c_clean_ipd(struct rk3x_i2c *i2c)
{
        i2c_writel(i2c, REG_INT_ALL, REG_IPD);
}

/**
 * Generate a START condition, which triggers a REG_INT_START interrupt.
 */
static void rk3x_i2c_start(struct rk3x_i2c *i2c)
{
        u32 val;

        rk3x_i2c_clean_ipd(i2c);
        i2c_writel(i2c, REG_INT_START, REG_IEN);

        /* enable adapter with correct mode, send START condition */
        val = REG_CON_EN | REG_CON_MOD(i2c->mode) | REG_CON_START;

        /* if we want to react to NACK, set ACTACK bit */
        if (!(i2c->msg->flags & I2C_M_IGNORE_NAK))
                val |= REG_CON_ACTACK;

        i2c_writel(i2c, val, REG_CON);
}

/**
 * Generate a STOP condition, which triggers a REG_INT_STOP interrupt.
 *
 * @error: Error code to return in rk3x_i2c_xfer
 */
static void rk3x_i2c_stop(struct rk3x_i2c *i2c, int error)
{
        unsigned int ctrl;

        i2c->processed = 0;
        i2c->msg = NULL;
        i2c->error = error;

        if (i2c->is_last_msg) {
                /* Enable stop interrupt */
                i2c_writel(i2c, REG_INT_STOP, REG_IEN);

                i2c->state = STATE_STOP;

                ctrl = i2c_readl(i2c, REG_CON);
                ctrl |= REG_CON_STOP;
                i2c_writel(i2c, ctrl, REG_CON);
        } else {
                /* Signal rk3x_i2c_xfer to start the next message. */
                i2c->busy = false;
                i2c->state = STATE_IDLE;

                /*
                 * The HW is actually not capable of REPEATED START. But we can
                 * get the intended effect by resetting its internal state
                 * and issuing an ordinary START.
                 */
                i2c_writel(i2c, 0, REG_CON);

                /* signal that we are finished with the current msg */
                wake_up(&i2c->wait);
        }
}

/**
 * Setup a read according to i2c->msg
 */
static void rk3x_i2c_prepare_read(struct rk3x_i2c *i2c)
{
        unsigned int len = i2c->msg->len - i2c->processed;
        u32 con;

        con = i2c_readl(i2c, REG_CON);

        /*
         * The hw can read up to 32 bytes at a time. If we need more than one
         * chunk, send an ACK after the last byte of the current chunk.
         */
        if (len > 32) {
                len = 32;
                con &= ~REG_CON_LASTACK;
        } else {
                con |= REG_CON_LASTACK;
        }

        /* make sure we are in plain RX mode if we read a second chunk */
        if (i2c->processed != 0) {
                con &= ~REG_CON_MOD_MASK;
                con |= REG_CON_MOD(REG_CON_MOD_RX);
        }

        i2c_writel(i2c, con, REG_CON);
        i2c_writel(i2c, len, REG_MRXCNT);
}

/**
 * Fill the transmit buffer with data from i2c->msg
 */
static void rk3x_i2c_fill_transmit_buf(struct rk3x_i2c *i2c)
{
        unsigned int i, j;
        u32 cnt = 0;
        u32 val;
        u8 byte;

        for (i = 0; i < 8; ++i) {
                val = 0;
                for (j = 0; j < 4; ++j) {
                        if ((i2c->processed == i2c->msg->len) && (cnt != 0))
                                break;

                        if (i2c->processed == 0 && cnt == 0)
                                byte = (i2c->addr & 0x7f) << 1;
                        else
                                byte = i2c->msg->buf[i2c->processed++];

                        val |= byte << (j * 8);
                        cnt++;
                }

                i2c_writel(i2c, val, TXBUFFER_BASE + 4 * i);

                if (i2c->processed == i2c->msg->len)
                        break;
        }

        i2c_writel(i2c, cnt, REG_MTXCNT);
}


/* IRQ handlers for individual states */

static void rk3x_i2c_handle_start(struct rk3x_i2c *i2c, unsigned int ipd)
{
        if (!(ipd & REG_INT_START)) {
                rk3x_i2c_stop(i2c, -EIO);
                dev_warn(i2c->dev, "unexpected irq in START: 0x%x\n", ipd);
                rk3x_i2c_clean_ipd(i2c);
                return;
        }

        /* ack interrupt */
        i2c_writel(i2c, REG_INT_START, REG_IPD);

        /* disable start bit */
        i2c_writel(i2c, i2c_readl(i2c, REG_CON) & ~REG_CON_START, REG_CON);

        /* enable appropriate interrupts and transition */
        if (i2c->mode == REG_CON_MOD_TX) {
                i2c_writel(i2c, REG_INT_MBTF | REG_INT_NAKRCV, REG_IEN);
                i2c->state = STATE_WRITE;
                rk3x_i2c_fill_transmit_buf(i2c);
        } else {
                /* in any other case, we are going to be reading. */
                i2c_writel(i2c, REG_INT_MBRF | REG_INT_NAKRCV, REG_IEN);
                i2c->state = STATE_READ;
                rk3x_i2c_prepare_read(i2c);
        }
}

static void rk3x_i2c_handle_write(struct rk3x_i2c *i2c, unsigned int ipd)
{
        if (!(ipd & REG_INT_MBTF)) {
                rk3x_i2c_stop(i2c, -EIO);
                dev_err(i2c->dev, "unexpected irq in WRITE: 0x%x\n", ipd);
                rk3x_i2c_clean_ipd(i2c);
                return;
        }

        /* ack interrupt */
        i2c_writel(i2c, REG_INT_MBTF, REG_IPD);

        /* are we finished? */
        if (i2c->processed == i2c->msg->len)
                rk3x_i2c_stop(i2c, i2c->error);
        else
                rk3x_i2c_fill_transmit_buf(i2c);
}

static void rk3x_i2c_handle_read(struct rk3x_i2c *i2c, unsigned int ipd)
{
        unsigned int i;
        unsigned int len = i2c->msg->len - i2c->processed;
        u32 uninitialized_var(val);
        u8 byte;

        /* we only care for MBRF here. */
        if (!(ipd & REG_INT_MBRF))
                return;

        /* ack interrupt */
        i2c_writel(i2c, REG_INT_MBRF, REG_IPD);

        /* Can only handle a maximum of 32 bytes at a time */
        if (len > 32)
                len = 32;

        /* read the data from receive buffer */
        for (i = 0; i < len; ++i) {
                if (i % 4 == 0)
                        val = i2c_readl(i2c, RXBUFFER_BASE + (i / 4) * 4);

                byte = (val >> ((i % 4) * 8)) & 0xff;
                i2c->msg->buf[i2c->processed++] = byte;
        }

        /* are we finished? */
        if (i2c->processed == i2c->msg->len)
                rk3x_i2c_stop(i2c, i2c->error);
        else
                rk3x_i2c_prepare_read(i2c);
}

static void rk3x_i2c_handle_stop(struct rk3x_i2c *i2c, unsigned int ipd)
{
        unsigned int con;

        if (!(ipd & REG_INT_STOP)) {
                rk3x_i2c_stop(i2c, -EIO);
                dev_err(i2c->dev, "unexpected irq in STOP: 0x%x\n", ipd);
                rk3x_i2c_clean_ipd(i2c);
                return;
        }

        /* ack interrupt */
        i2c_writel(i2c, REG_INT_STOP, REG_IPD);

        /* disable STOP bit */
        con = i2c_readl(i2c, REG_CON);
        con &= ~REG_CON_STOP;
        i2c_writel(i2c, con, REG_CON);

        i2c->busy = false;
        i2c->state = STATE_IDLE;

        /* signal rk3x_i2c_xfer that we are finished */
        wake_up(&i2c->wait);
}

static irqreturn_t rk3x_i2c_irq(int irqno, void *dev_id)
{
        struct rk3x_i2c *i2c = dev_id;
        unsigned int ipd;

        spin_lock(&i2c->lock);

        ipd = i2c_readl(i2c, REG_IPD);
        if (i2c->state == STATE_IDLE) {
                dev_warn(i2c->dev, "irq in STATE_IDLE, ipd = 0x%x\n", ipd);
                rk3x_i2c_clean_ipd(i2c);
                goto out;
        }

        dev_dbg(i2c->dev, "IRQ: state %d, ipd: %x\n", i2c->state, ipd);

        /* Clean interrupt bits we don't care about */
        ipd &= ~(REG_INT_BRF | REG_INT_BTF);

        if (ipd & REG_INT_NAKRCV) {
                /*
                 * We got a NACK in the last operation. Depending on whether
                 * IGNORE_NAK is set, we have to stop the operation and report
                 * an error.
                 */
                i2c_writel(i2c, REG_INT_NAKRCV, REG_IPD);

                ipd &= ~REG_INT_NAKRCV;

                if (!(i2c->msg->flags & I2C_M_IGNORE_NAK))
                        rk3x_i2c_stop(i2c, -ENXIO);
        }

        /* is there anything left to handle? */
        if ((ipd & REG_INT_ALL) == 0)
                goto out;

        switch (i2c->state) {
        case STATE_START:
                rk3x_i2c_handle_start(i2c, ipd);
                break;
        case STATE_WRITE:
                rk3x_i2c_handle_write(i2c, ipd);
                break;
        case STATE_READ:
                rk3x_i2c_handle_read(i2c, ipd);
                break;
        case STATE_STOP:
                rk3x_i2c_handle_stop(i2c, ipd);
                break;
        case STATE_IDLE:
                break;
        }

out:
        spin_unlock(&i2c->lock);
        return IRQ_HANDLED;
}

/**
 * Calculate divider values for desired SCL frequency
 *
 * @clk_rate: I2C input clock rate
 * @scl_rate: Desired SCL rate
 * @scl_rise_ns: How many ns it takes for SCL to rise.
 * @scl_fall_ns: How many ns it takes for SCL to fall.
 * @sda_fall_ns: How many ns it takes for SDA to fall.
 * @div_low: Divider output for low
 * @div_high: Divider output for high
 *
 * Returns: 0 on success, -EINVAL if the goal SCL rate is too slow. In that case
 * a best-effort divider value is returned in divs. If the target rate is
 * too high, we silently use the highest possible rate.
 */
static int rk3x_i2c_calc_divs(unsigned long clk_rate, unsigned long scl_rate,
                              unsigned long scl_rise_ns,
                              unsigned long scl_fall_ns,
                              unsigned long sda_fall_ns,
                              unsigned long *div_low, unsigned long *div_high)
{
        unsigned long spec_min_low_ns, spec_min_high_ns;
        unsigned long spec_setup_start, spec_max_data_hold_ns;
        unsigned long data_hold_buffer_ns;

        unsigned long min_low_ns, min_high_ns;
        unsigned long max_low_ns, min_total_ns;

        unsigned long clk_rate_khz, scl_rate_khz;

        unsigned long min_low_div, min_high_div;
        unsigned long max_low_div;

        unsigned long min_div_for_hold, min_total_div;
        unsigned long extra_div, extra_low_div, ideal_low_div;

        int ret = 0;

        /* Only support standard-mode and fast-mode */
        if (WARN_ON(scl_rate > 400000))
                scl_rate = 400000;

        /* prevent scl_rate_khz from becoming 0 */
        if (WARN_ON(scl_rate < 1000))
                scl_rate = 1000;

        /*
         * min_low_ns:  The minimum number of ns we need to hold low to
         *              meet I2C specification, should include fall time.
         * min_high_ns: The minimum number of ns we need to hold high to
         *              meet I2C specification, should include rise time.
         * max_low_ns:  The maximum number of ns we can hold low to meet
         *              I2C specification.
         *
         * Note: max_low_ns should be (maximum data hold time * 2 - buffer)
         *       This is because the i2c host on Rockchip holds the data line
         *       for half the low time.
         */
        if (scl_rate <= 100000) {
                /* Standard-mode */
                spec_min_low_ns = 4700;
                spec_setup_start = 4700;
                spec_min_high_ns = 4000;
                spec_max_data_hold_ns = 3450;
                data_hold_buffer_ns = 50;
        } else {
                /* Fast-mode */
                spec_min_low_ns = 1300;
                spec_setup_start = 600;
                spec_min_high_ns = 600;
                spec_max_data_hold_ns = 900;
                data_hold_buffer_ns = 50;
        }
        min_high_ns = scl_rise_ns + spec_min_high_ns;

        /*
         * Timings for repeated start:
         * - controller appears to drop SDA at .875x (7/8) programmed clk high.
         * - controller appears to keep SCL high for 2x programmed clk high.
         *
         * We need to account for those rules in picking our "high" time so
         * we meet tSU;STA and tHD;STA times.
         */
        min_high_ns = max(min_high_ns,
                DIV_ROUND_UP((scl_rise_ns + spec_setup_start) * 1000, 875));
        min_high_ns = max(min_high_ns,
                DIV_ROUND_UP((scl_rise_ns + spec_setup_start +
                              sda_fall_ns + spec_min_high_ns), 2));

        min_low_ns = scl_fall_ns + spec_min_low_ns;
        max_low_ns = spec_max_data_hold_ns * 2 - data_hold_buffer_ns;
        min_total_ns = min_low_ns + min_high_ns;

        /* Adjust to avoid overflow */
        clk_rate_khz = DIV_ROUND_UP(clk_rate, 1000);
        scl_rate_khz = scl_rate / 1000;

        /*
         * We need the total div to be >= this number
         * so we don't clock too fast.
         */
        min_total_div = DIV_ROUND_UP(clk_rate_khz, scl_rate_khz * 8);

        /* These are the min dividers needed for min hold times. */
        min_low_div = DIV_ROUND_UP(clk_rate_khz * min_low_ns, 8 * 1000000);
        min_high_div = DIV_ROUND_UP(clk_rate_khz * min_high_ns, 8 * 1000000);
        min_div_for_hold = (min_low_div + min_high_div);

        /*
         * This is the maximum divider so we don't go over the maximum.
         * We don't round up here (we round down) since this is a maximum.
         */
        max_low_div = clk_rate_khz * max_low_ns / (8 * 1000000);

        if (min_low_div > max_low_div) {
                WARN_ONCE(true,
                          "Conflicting, min_low_div %lu, max_low_div %lu\n",
                          min_low_div, max_low_div);
                max_low_div = min_low_div;
        }

        if (min_div_for_hold > min_total_div) {
                /*
                 * Time needed to meet hold requirements is important.
                 * Just use that.
                 */
                *div_low = min_low_div;
                *div_high = min_high_div;
        } else {
                /*
                 * We've got to distribute some time among the low and high
                 * so we don't run too fast.
                 */
                extra_div = min_total_div - min_div_for_hold;

                /*
                 * We'll try to split things up perfectly evenly,
                 * biasing slightly towards having a higher div
                 * for low (spend more time low).
                 */
                ideal_low_div = DIV_ROUND_UP(clk_rate_khz * min_low_ns,
                                             scl_rate_khz * 8 * min_total_ns);

                /* Don't allow it to go over the maximum */
                if (ideal_low_div > max_low_div)
                        ideal_low_div = max_low_div;

                /*
                 * Handle when the ideal low div is going to take up
                 * more than we have.
                 */
                if (ideal_low_div > min_low_div + extra_div)
                        ideal_low_div = min_low_div + extra_div;

                /* Give low the "ideal" and give high whatever extra is left */
                extra_low_div = ideal_low_div - min_low_div;
                *div_low = ideal_low_div;
                *div_high = min_high_div + (extra_div - extra_low_div);
        }

        /*
         * Adjust to the fact that the hardware has an implicit "+1".
         * NOTE: Above calculations always produce div_low > 0 and div_high > 0.
         */
        *div_low = *div_low - 1;
        *div_high = *div_high - 1;

        /* Maximum divider supported by hw is 0xffff */
        if (*div_low > 0xffff) {
                *div_low = 0xffff;
                ret = -EINVAL;
        }

        if (*div_high > 0xffff) {
                *div_high = 0xffff;
                ret = -EINVAL;
        }

        return ret;
}

static void rk3x_i2c_adapt_div(struct rk3x_i2c *i2c, unsigned long clk_rate)
{
        unsigned long div_low, div_high;
        u64 t_low_ns, t_high_ns;
        int ret;

        ret = rk3x_i2c_calc_divs(clk_rate, i2c->scl_frequency, i2c->scl_rise_ns,
                                 i2c->scl_fall_ns, i2c->sda_fall_ns,
                                 &div_low, &div_high);
        WARN_ONCE(ret != 0, "Could not reach SCL freq %u", i2c->scl_frequency);

        clk_enable(i2c->clk);
        i2c_writel(i2c, (div_high << 16) | (div_low & 0xffff), REG_CLKDIV);
        clk_disable(i2c->clk);

        t_low_ns = div_u64(((u64)div_low + 1) * 8 * 1000000000, clk_rate);
        t_high_ns = div_u64(((u64)div_high + 1) * 8 * 1000000000, clk_rate);
        dev_dbg(i2c->dev,
                "CLK %lukhz, Req %uns, Act low %lluns high %lluns\n",
                clk_rate / 1000,
                1000000000 / i2c->scl_frequency,
                t_low_ns, t_high_ns);
}

/**
 * rk3x_i2c_clk_notifier_cb - Clock rate change callback
 * @nb:         Pointer to notifier block
 * @event:      Notification reason
 * @data:       Pointer to notification data object
 *
 * The callback checks whether a valid bus frequency can be generated after the
 * change. If so, the change is acknowledged, otherwise the change is aborted.
 * New dividers are written to the HW in the pre- or post change notification
 * depending on the scaling direction.
 *
 * Code adapted from i2c-cadence.c.
 *
 * Return:      NOTIFY_STOP if the rate change should be aborted, NOTIFY_OK
 *              to acknowedge the change, NOTIFY_DONE if the notification is
 *              considered irrelevant.
 */
static int rk3x_i2c_clk_notifier_cb(struct notifier_block *nb, unsigned long
                                    event, void *data)
{
        struct clk_notifier_data *ndata = data;
        struct rk3x_i2c *i2c = container_of(nb, struct rk3x_i2c, clk_rate_nb);
        unsigned long div_low, div_high;

        switch (event) {
        case PRE_RATE_CHANGE:
                if (rk3x_i2c_calc_divs(ndata->new_rate, i2c->scl_frequency,
                                       i2c->scl_rise_ns, i2c->scl_fall_ns,
                                       i2c->sda_fall_ns,
                                       &div_low, &div_high) != 0)
                        return NOTIFY_STOP;

                /* scale up */
                if (ndata->new_rate > ndata->old_rate)
                        rk3x_i2c_adapt_div(i2c, ndata->new_rate);

                return NOTIFY_OK;
        case POST_RATE_CHANGE:
                /* scale down */
                if (ndata->new_rate < ndata->old_rate)
                        rk3x_i2c_adapt_div(i2c, ndata->new_rate);
                return NOTIFY_OK;
        case ABORT_RATE_CHANGE:
                /* scale up */
                if (ndata->new_rate > ndata->old_rate)
                        rk3x_i2c_adapt_div(i2c, ndata->old_rate);
                return NOTIFY_OK;
        default:
                return NOTIFY_DONE;
        }
}

/**
 * Setup I2C registers for an I2C operation specified by msgs, num.
 *
 * Must be called with i2c->lock held.
 *
 * @msgs: I2C msgs to process
 * @num: Number of msgs
 *
 * returns: Number of I2C msgs processed or negative in case of error
 */
static int rk3x_i2c_setup(struct rk3x_i2c *i2c, struct i2c_msg *msgs, int num)
{
        u32 addr = (msgs[0].addr & 0x7f) << 1;
        int ret = 0;

        /*
         * The I2C adapter can issue a small (len < 4) write packet before
         * reading. This speeds up SMBus-style register reads.
         * The MRXADDR/MRXRADDR hold the slave address and the slave register
         * address in this case.
         */

        if (num >= 2 && msgs[0].len < 4 &&
            !(msgs[0].flags & I2C_M_RD) && (msgs[1].flags & I2C_M_RD)) {
                u32 reg_addr = 0;
                int i;

                dev_dbg(i2c->dev, "Combined write/read from addr 0x%x\n",
                        addr >> 1);

                /* Fill MRXRADDR with the register address(es) */
                for (i = 0; i < msgs[0].len; ++i) {
                        reg_addr |= msgs[0].buf[i] << (i * 8);
                        reg_addr |= REG_MRXADDR_VALID(i);
                }

                /* msgs[0] is handled by hw. */
                i2c->msg = &msgs[1];

                i2c->mode = REG_CON_MOD_REGISTER_TX;

                i2c_writel(i2c, addr | REG_MRXADDR_VALID(0), REG_MRXADDR);
                i2c_writel(i2c, reg_addr, REG_MRXRADDR);

                ret = 2;
        } else {
                /*
                 * We'll have to do it the boring way and process the msgs
                 * one-by-one.
                 */

                if (msgs[0].flags & I2C_M_RD) {
                        addr |= 1; /* set read bit */

                        /*
                         * We have to transmit the slave addr first. Use
                         * MOD_REGISTER_TX for that purpose.
                         */
                        i2c->mode = REG_CON_MOD_REGISTER_TX;
                        i2c_writel(i2c, addr | REG_MRXADDR_VALID(0),
                                   REG_MRXADDR);
                        i2c_writel(i2c, 0, REG_MRXRADDR);
                } else {
                        i2c->mode = REG_CON_MOD_TX;
                }

                i2c->msg = &msgs[0];

                ret = 1;
        }

        i2c->addr = msgs[0].addr;
        i2c->busy = true;
        i2c->state = STATE_START;
        i2c->processed = 0;
        i2c->error = 0;

        rk3x_i2c_clean_ipd(i2c);

        return ret;
}

static int rk3x_i2c_xfer(struct i2c_adapter *adap,
                         struct i2c_msg *msgs, int num)
{
        struct rk3x_i2c *i2c = (struct rk3x_i2c *)adap->algo_data;
        unsigned long timeout, flags;
        int ret = 0;
        int i;

        spin_lock_irqsave(&i2c->lock, flags);

        clk_enable(i2c->clk);

        i2c->is_last_msg = false;

        /*
         * Process msgs. We can handle more than one message at once (see
         * rk3x_i2c_setup()).
         */
        for (i = 0; i < num; i += ret) {
                ret = rk3x_i2c_setup(i2c, msgs + i, num - i);

                if (ret < 0) {
                        dev_err(i2c->dev, "rk3x_i2c_setup() failed\n");
                        break;
                }

                if (i + ret >= num)
                        i2c->is_last_msg = true;

                spin_unlock_irqrestore(&i2c->lock, flags);

                rk3x_i2c_start(i2c);

                timeout = wait_event_timeout(i2c->wait, !i2c->busy,
                                             msecs_to_jiffies(WAIT_TIMEOUT));

                spin_lock_irqsave(&i2c->lock, flags);

                if (timeout == 0) {
                        dev_err(i2c->dev, "timeout, ipd: 0x%02x, state: %d\n",
                                i2c_readl(i2c, REG_IPD), i2c->state);

                        /* Force a STOP condition without interrupt */
                        i2c_writel(i2c, 0, REG_IEN);
                        i2c_writel(i2c, REG_CON_EN | REG_CON_STOP, REG_CON);

                        i2c->state = STATE_IDLE;

                        ret = -ETIMEDOUT;
                        break;
                }

                if (i2c->error) {
                        ret = i2c->error;
                        break;
                }
        }

        clk_disable(i2c->clk);
        spin_unlock_irqrestore(&i2c->lock, flags);

        return ret < 0 ? ret : num;
}

static u32 rk3x_i2c_func(struct i2c_adapter *adap)
{
        return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL | I2C_FUNC_PROTOCOL_MANGLING;
}

static const struct i2c_algorithm rk3x_i2c_algorithm = {
        .master_xfer            = rk3x_i2c_xfer,
        .functionality          = rk3x_i2c_func,
};

static struct rk3x_i2c_soc_data soc_data[3] = {
        { .grf_offset = 0x154 }, /* rk3066 */
        { .grf_offset = 0x0a4 }, /* rk3188 */
        { .grf_offset = -1 },    /* no I2C switching needed */
};

static const struct of_device_id rk3x_i2c_match[] = {
        { .compatible = "rockchip,rk3066-i2c", .data = (void *)&soc_data[0] },
        { .compatible = "rockchip,rk3188-i2c", .data = (void *)&soc_data[1] },
        { .compatible = "rockchip,rk3288-i2c", .data = (void *)&soc_data[2] },
        {},
};

static int rk3x_i2c_probe(struct platform_device *pdev)
{
        struct device_node *np = pdev->dev.of_node;
        const struct of_device_id *match;
        struct rk3x_i2c *i2c;
        struct resource *mem;
        int ret = 0;
        int bus_nr;
        u32 value;
        int irq;
        unsigned long clk_rate;

        i2c = devm_kzalloc(&pdev->dev, sizeof(struct rk3x_i2c), GFP_KERNEL);
        if (!i2c)
                return -ENOMEM;

        match = of_match_node(rk3x_i2c_match, np);
        i2c->soc_data = (struct rk3x_i2c_soc_data *)match->data;

        if (of_property_read_u32(pdev->dev.of_node, "clock-frequency",
                                 &i2c->scl_frequency)) {
                dev_info(&pdev->dev, "using default SCL frequency: %d\n",
                         DEFAULT_SCL_RATE);
                i2c->scl_frequency = DEFAULT_SCL_RATE;
        }

        if (i2c->scl_frequency == 0 || i2c->scl_frequency > 400 * 1000) {
                dev_warn(&pdev->dev, "invalid SCL frequency specified.\n");
                dev_warn(&pdev->dev, "using default SCL frequency: %d\n",
                         DEFAULT_SCL_RATE);
                i2c->scl_frequency = DEFAULT_SCL_RATE;
        }

        /*
         * Read rise and fall time from device tree. If not available use
         * the default maximum timing from the specification.
         */
        if (of_property_read_u32(pdev->dev.of_node, "i2c-scl-rising-time-ns",
                                 &i2c->scl_rise_ns)) {
                if (i2c->scl_frequency <= 100000)
                        i2c->scl_rise_ns = 1000;
                else
                        i2c->scl_rise_ns = 300;
        }
        if (of_property_read_u32(pdev->dev.of_node, "i2c-scl-falling-time-ns",
                                 &i2c->scl_fall_ns))
                i2c->scl_fall_ns = 300;
        if (of_property_read_u32(pdev->dev.of_node, "i2c-sda-falling-time-ns",
                                 &i2c->scl_fall_ns))
                i2c->sda_fall_ns = i2c->scl_fall_ns;

        strlcpy(i2c->adap.name, "rk3x-i2c", sizeof(i2c->adap.name));
        i2c->adap.owner = THIS_MODULE;
        i2c->adap.algo = &rk3x_i2c_algorithm;
        i2c->adap.retries = 3;
        i2c->adap.dev.of_node = np;
        i2c->adap.algo_data = i2c;
        i2c->adap.dev.parent = &pdev->dev;

        i2c->dev = &pdev->dev;

        spin_lock_init(&i2c->lock);
        init_waitqueue_head(&i2c->wait);

        i2c->clk = devm_clk_get(&pdev->dev, NULL);
        if (IS_ERR(i2c->clk)) {
                dev_err(&pdev->dev, "cannot get clock\n");
                return PTR_ERR(i2c->clk);
        }

        mem = platform_get_resource(pdev, IORESOURCE_MEM, 0);
        i2c->regs = devm_ioremap_resource(&pdev->dev, mem);
        if (IS_ERR(i2c->regs))
                return PTR_ERR(i2c->regs);

        /* Try to set the I2C adapter number from dt */
        bus_nr = of_alias_get_id(np, "i2c");

        /*
         * Switch to new interface if the SoC also offers the old one.
         * The control bit is located in the GRF register space.
         */
        if (i2c->soc_data->grf_offset >= 0) {
                struct regmap *grf;

                grf = syscon_regmap_lookup_by_phandle(np, "rockchip,grf");
                if (IS_ERR(grf)) {
                        dev_err(&pdev->dev,
                                "rk3x-i2c needs 'rockchip,grf' property\n");
                        return PTR_ERR(grf);
                }

                if (bus_nr < 0) {
                        dev_err(&pdev->dev, "rk3x-i2c needs i2cX alias");
                        return -EINVAL;
                }

                /* 27+i: write mask, 11+i: value */
                value = BIT(27 + bus_nr) | BIT(11 + bus_nr);

                ret = regmap_write(grf, i2c->soc_data->grf_offset, value);
                if (ret != 0) {
                        dev_err(i2c->dev, "Could not write to GRF: %d\n", ret);
                        return ret;
                }
        }

        /* IRQ setup */
        irq = platform_get_irq(pdev, 0);
        if (irq < 0) {
                dev_err(&pdev->dev, "cannot find rk3x IRQ\n");
                return irq;
        }

        ret = devm_request_irq(&pdev->dev, irq, rk3x_i2c_irq,
                               0, dev_name(&pdev->dev), i2c);
        if (ret < 0) {
                dev_err(&pdev->dev, "cannot request IRQ\n");
                return ret;
        }

        platform_set_drvdata(pdev, i2c);

        ret = clk_prepare(i2c->clk);
        if (ret < 0) {
                dev_err(&pdev->dev, "Could not prepare clock\n");
                return ret;
        }

        i2c->clk_rate_nb.notifier_call = rk3x_i2c_clk_notifier_cb;
        ret = clk_notifier_register(i2c->clk, &i2c->clk_rate_nb);
        if (ret != 0) {
                dev_err(&pdev->dev, "Unable to register clock notifier\n");
                goto err_clk;
        }

        clk_rate = clk_get_rate(i2c->clk);
        rk3x_i2c_adapt_div(i2c, clk_rate);

        ret = i2c_add_adapter(&i2c->adap);
        if (ret < 0) {
                dev_err(&pdev->dev, "Could not register adapter\n");
                goto err_clk_notifier;
        }

        dev_info(&pdev->dev, "Initialized RK3xxx I2C bus at %p\n", i2c->regs);

        return 0;

err_clk_notifier:
        clk_notifier_unregister(i2c->clk, &i2c->clk_rate_nb);
err_clk:
        clk_unprepare(i2c->clk);
        return ret;
}

static int rk3x_i2c_remove(struct platform_device *pdev)
{
        struct rk3x_i2c *i2c = platform_get_drvdata(pdev);

        i2c_del_adapter(&i2c->adap);

        clk_notifier_unregister(i2c->clk, &i2c->clk_rate_nb);
        clk_unprepare(i2c->clk);

        return 0;
}

static struct platform_driver rk3x_i2c_driver = {
        .probe   = rk3x_i2c_probe,
        .remove  = rk3x_i2c_remove,
        .driver  = {
                .name  = "rk3x-i2c",
                .of_match_table = rk3x_i2c_match,
        },
};

module_platform_driver(rk3x_i2c_driver);

MODULE_DESCRIPTION("Rockchip RK3xxx I2C Bus driver");
MODULE_AUTHOR("Max Schwarz <max.schwarz@online.de>");
MODULE_LICENSE("GPL v2");