i2c: Add driver for Cadence I2C controller

[deliverable/linux.git] / drivers / i2c / busses / i2c-cadence.c

/*
 * I2C bus driver for the Cadence I2C controller.
 *
 * Copyright (C) 2009 - 2014 Xilinx, Inc.
 *
 * 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/clk.h>
#include <linux/delay.h>
#include <linux/i2c.h>
#include <linux/interrupt.h>
#include <linux/io.h>
#include <linux/module.h>
#include <linux/platform_device.h>

/* Register offsets for the I2C device. */
#define CDNS_I2C_CR_OFFSET              0x00 /* Control Register, RW */
#define CDNS_I2C_SR_OFFSET              0x04 /* Status Register, RO */
#define CDNS_I2C_ADDR_OFFSET            0x08 /* I2C Address Register, RW */
#define CDNS_I2C_DATA_OFFSET            0x0C /* I2C Data Register, RW */
#define CDNS_I2C_ISR_OFFSET             0x10 /* IRQ Status Register, RW */
#define CDNS_I2C_XFER_SIZE_OFFSET       0x14 /* Transfer Size Register, RW */
#define CDNS_I2C_TIME_OUT_OFFSET        0x1C /* Time Out Register, RW */
#define CDNS_I2C_IER_OFFSET             0x24 /* IRQ Enable Register, WO */
#define CDNS_I2C_IDR_OFFSET             0x28 /* IRQ Disable Register, WO */

/* Control Register Bit mask definitions */
#define CDNS_I2C_CR_HOLD                BIT(4) /* Hold Bus bit */
#define CDNS_I2C_CR_ACK_EN              BIT(3)
#define CDNS_I2C_CR_NEA                 BIT(2)
#define CDNS_I2C_CR_MS                  BIT(1)
/* Read or Write Master transfer 0 = Transmitter, 1 = Receiver */
#define CDNS_I2C_CR_RW                  BIT(0)
/* 1 = Auto init FIFO to zeroes */
#define CDNS_I2C_CR_CLR_FIFO            BIT(6)
#define CDNS_I2C_CR_DIVA_SHIFT          14
#define CDNS_I2C_CR_DIVA_MASK           (3 << CDNS_I2C_CR_DIVA_SHIFT)
#define CDNS_I2C_CR_DIVB_SHIFT          8
#define CDNS_I2C_CR_DIVB_MASK           (0x3f << CDNS_I2C_CR_DIVB_SHIFT)

/* Status Register Bit mask definitions */
#define CDNS_I2C_SR_BA          BIT(8)
#define CDNS_I2C_SR_RXDV        BIT(5)

/*
 * I2C Address Register Bit mask definitions
 * Normal addressing mode uses [6:0] bits. Extended addressing mode uses [9:0]
 * bits. A write access to this register always initiates a transfer if the I2C
 * is in master mode.
 */
#define CDNS_I2C_ADDR_MASK      0x000003FF /* I2C Address Mask */

/*
 * I2C Interrupt Registers Bit mask definitions
 * All the four interrupt registers (Status/Mask/Enable/Disable) have the same
 * bit definitions.
 */
#define CDNS_I2C_IXR_ARB_LOST           BIT(9)
#define CDNS_I2C_IXR_RX_UNF             BIT(7)
#define CDNS_I2C_IXR_TX_OVF             BIT(6)
#define CDNS_I2C_IXR_RX_OVF             BIT(5)
#define CDNS_I2C_IXR_SLV_RDY            BIT(4)
#define CDNS_I2C_IXR_TO                 BIT(3)
#define CDNS_I2C_IXR_NACK               BIT(2)
#define CDNS_I2C_IXR_DATA               BIT(1)
#define CDNS_I2C_IXR_COMP               BIT(0)

#define CDNS_I2C_IXR_ALL_INTR_MASK      (CDNS_I2C_IXR_ARB_LOST | \
                                         CDNS_I2C_IXR_RX_UNF | \
                                         CDNS_I2C_IXR_TX_OVF | \
                                         CDNS_I2C_IXR_RX_OVF | \
                                         CDNS_I2C_IXR_SLV_RDY | \
                                         CDNS_I2C_IXR_TO | \
                                         CDNS_I2C_IXR_NACK | \
                                         CDNS_I2C_IXR_DATA | \
                                         CDNS_I2C_IXR_COMP)

#define CDNS_I2C_IXR_ERR_INTR_MASK      (CDNS_I2C_IXR_ARB_LOST | \
                                         CDNS_I2C_IXR_RX_UNF | \
                                         CDNS_I2C_IXR_TX_OVF | \
                                         CDNS_I2C_IXR_RX_OVF | \
                                         CDNS_I2C_IXR_NACK)

#define CDNS_I2C_ENABLED_INTR_MASK      (CDNS_I2C_IXR_ARB_LOST | \
                                         CDNS_I2C_IXR_RX_UNF | \
                                         CDNS_I2C_IXR_TX_OVF | \
                                         CDNS_I2C_IXR_RX_OVF | \
                                         CDNS_I2C_IXR_NACK | \
                                         CDNS_I2C_IXR_DATA | \
                                         CDNS_I2C_IXR_COMP)

#define CDNS_I2C_TIMEOUT                msecs_to_jiffies(1000)

#define CDNS_I2C_FIFO_DEPTH             16
/* FIFO depth at which the DATA interrupt occurs */
#define CDNS_I2C_DATA_INTR_DEPTH        (CDNS_I2C_FIFO_DEPTH - 2)
#define CDNS_I2C_MAX_TRANSFER_SIZE      255
/* Transfer size in multiples of data interrupt depth */
#define CDNS_I2C_TRANSFER_SIZE  (CDNS_I2C_MAX_TRANSFER_SIZE - 3)

#define DRIVER_NAME             "cdns-i2c"

#define CDNS_I2C_SPEED_MAX      400000
#define CDNS_I2C_SPEED_DEFAULT  100000

#define CDNS_I2C_DIVA_MAX       4
#define CDNS_I2C_DIVB_MAX       64

#define cdns_i2c_readreg(offset)       readl_relaxed(id->membase + offset)
#define cdns_i2c_writereg(val, offset) writel_relaxed(val, id->membase + offset)

/**
 * struct cdns_i2c - I2C device private data structure
 * @membase:            Base address of the I2C device
 * @adap:               I2C adapter instance
 * @p_msg:              Message pointer
 * @err_status:         Error status in Interrupt Status Register
 * @xfer_done:          Transfer complete status
 * @p_send_buf:         Pointer to transmit buffer
 * @p_recv_buf:         Pointer to receive buffer
 * @suspended:          Flag holding the device's PM status
 * @send_count:         Number of bytes still expected to send
 * @recv_count:         Number of bytes still expected to receive
 * @irq:                IRQ number
 * @input_clk:          Input clock to I2C controller
 * @i2c_clk:            Maximum I2C clock speed
 * @bus_hold_flag:      Flag used in repeated start for clearing HOLD bit
 * @clk:                Pointer to struct clk
 * @clk_rate_change_nb: Notifier block for clock rate changes
 */
struct cdns_i2c {
        void __iomem *membase;
        struct i2c_adapter adap;
        struct i2c_msg *p_msg;
        int err_status;
        struct completion xfer_done;
        unsigned char *p_send_buf;
        unsigned char *p_recv_buf;
        u8 suspended;
        unsigned int send_count;
        unsigned int recv_count;
        int irq;
        unsigned long input_clk;
        unsigned int i2c_clk;
        unsigned int bus_hold_flag;
        struct clk *clk;
        struct notifier_block clk_rate_change_nb;
};

#define to_cdns_i2c(_nb)        container_of(_nb, struct cdns_i2c, \
                                             clk_rate_change_nb)

/**
 * cdns_i2c_clear_bus_hold() - Clear bus hold bit
 * @id: Pointer to driver data struct
 *
 * Helper to clear the controller's bus hold bit.
 */
static void cdns_i2c_clear_bus_hold(struct cdns_i2c *id)
{
        u32 reg = cdns_i2c_readreg(CDNS_I2C_CR_OFFSET);
        if (reg & CDNS_I2C_CR_HOLD)
                cdns_i2c_writereg(reg & ~CDNS_I2C_CR_HOLD, CDNS_I2C_CR_OFFSET);
}

/**
 * cdns_i2c_isr - Interrupt handler for the I2C device
 * @irq:        irq number for the I2C device
 * @ptr:        void pointer to cdns_i2c structure
 *
 * This function handles the data interrupt, transfer complete interrupt and
 * the error interrupts of the I2C device.
 *
 * Return: IRQ_HANDLED always
 */
static irqreturn_t cdns_i2c_isr(int irq, void *ptr)
{
        unsigned int isr_status, avail_bytes;
        unsigned int bytes_to_recv, bytes_to_send;
        struct cdns_i2c *id = ptr;
        /* Signal completion only after everything is updated */
        int done_flag = 0;
        irqreturn_t status = IRQ_NONE;

        isr_status = cdns_i2c_readreg(CDNS_I2C_ISR_OFFSET);

        /* Handling nack and arbitration lost interrupt */
        if (isr_status & (CDNS_I2C_IXR_NACK | CDNS_I2C_IXR_ARB_LOST)) {
                done_flag = 1;
                status = IRQ_HANDLED;
        }

        /* Handling Data interrupt */
        if ((isr_status & CDNS_I2C_IXR_DATA) &&
                        (id->recv_count >= CDNS_I2C_DATA_INTR_DEPTH)) {
                /* Always read data interrupt threshold bytes */
                bytes_to_recv = CDNS_I2C_DATA_INTR_DEPTH;
                id->recv_count -= CDNS_I2C_DATA_INTR_DEPTH;
                avail_bytes = cdns_i2c_readreg(CDNS_I2C_XFER_SIZE_OFFSET);

                /*
                 * if the tranfer size register value is zero, then
                 * check for the remaining bytes and update the
                 * transfer size register.
                 */
                if (!avail_bytes) {
                        if (id->recv_count > CDNS_I2C_TRANSFER_SIZE)
                                cdns_i2c_writereg(CDNS_I2C_TRANSFER_SIZE,
                                                CDNS_I2C_XFER_SIZE_OFFSET);
                        else
                                cdns_i2c_writereg(id->recv_count,
                                                CDNS_I2C_XFER_SIZE_OFFSET);
                }

                /* Process the data received */
                while (bytes_to_recv--)
                        *(id->p_recv_buf)++ =
                                cdns_i2c_readreg(CDNS_I2C_DATA_OFFSET);

                if (!id->bus_hold_flag &&
                                (id->recv_count <= CDNS_I2C_FIFO_DEPTH))
                        cdns_i2c_clear_bus_hold(id);

                status = IRQ_HANDLED;
        }

        /* Handling Transfer Complete interrupt */
        if (isr_status & CDNS_I2C_IXR_COMP) {
                if (!id->p_recv_buf) {
                        /*
                         * If the device is sending data If there is further
                         * data to be sent. Calculate the available space
                         * in FIFO and fill the FIFO with that many bytes.
                         */
                        if (id->send_count) {
                                avail_bytes = CDNS_I2C_FIFO_DEPTH -
                                    cdns_i2c_readreg(CDNS_I2C_XFER_SIZE_OFFSET);
                                if (id->send_count > avail_bytes)
                                        bytes_to_send = avail_bytes;
                                else
                                        bytes_to_send = id->send_count;

                                while (bytes_to_send--) {
                                        cdns_i2c_writereg(
                                                (*(id->p_send_buf)++),
                                                 CDNS_I2C_DATA_OFFSET);
                                        id->send_count--;
                                }
                        } else {
                                /*
                                 * Signal the completion of transaction and
                                 * clear the hold bus bit if there are no
                                 * further messages to be processed.
                                 */
                                done_flag = 1;
                        }
                        if (!id->send_count && !id->bus_hold_flag)
                                cdns_i2c_clear_bus_hold(id);
                } else {
                        if (!id->bus_hold_flag)
                                cdns_i2c_clear_bus_hold(id);
                        /*
                         * If the device is receiving data, then signal
                         * the completion of transaction and read the data
                         * present in the FIFO. Signal the completion of
                         * transaction.
                         */
                        while (cdns_i2c_readreg(CDNS_I2C_SR_OFFSET) &
                                        CDNS_I2C_SR_RXDV) {
                                *(id->p_recv_buf)++ =
                                        cdns_i2c_readreg(CDNS_I2C_DATA_OFFSET);
                                id->recv_count--;
                        }
                        done_flag = 1;
                }

                status = IRQ_HANDLED;
        }

        /* Update the status for errors */
        id->err_status = isr_status & CDNS_I2C_IXR_ERR_INTR_MASK;
        if (id->err_status)
                status = IRQ_HANDLED;

        cdns_i2c_writereg(isr_status, CDNS_I2C_ISR_OFFSET);

        if (done_flag)
                complete(&id->xfer_done);

        return status;
}

/**
 * cdns_i2c_mrecv - Prepare and start a master receive operation
 * @id:         pointer to the i2c device structure
 */
static void cdns_i2c_mrecv(struct cdns_i2c *id)
{
        unsigned int ctrl_reg;
        unsigned int isr_status;

        id->p_recv_buf = id->p_msg->buf;
        id->recv_count = id->p_msg->len;

        /* Put the controller in master receive mode and clear the FIFO */
        ctrl_reg = cdns_i2c_readreg(CDNS_I2C_CR_OFFSET);
        ctrl_reg |= CDNS_I2C_CR_RW | CDNS_I2C_CR_CLR_FIFO;

        if (id->p_msg->flags & I2C_M_RECV_LEN)
                id->recv_count = I2C_SMBUS_BLOCK_MAX + 1;

        /*
         * Check for the message size against FIFO depth and set the
         * 'hold bus' bit if it is greater than FIFO depth.
         */
        if (id->recv_count > CDNS_I2C_FIFO_DEPTH)
                ctrl_reg |= CDNS_I2C_CR_HOLD;

        cdns_i2c_writereg(ctrl_reg, CDNS_I2C_CR_OFFSET);

        /* Clear the interrupts in interrupt status register */
        isr_status = cdns_i2c_readreg(CDNS_I2C_ISR_OFFSET);
        cdns_i2c_writereg(isr_status, CDNS_I2C_ISR_OFFSET);

        /*
         * The no. of bytes to receive is checked against the limit of
         * max transfer size. Set transfer size register with no of bytes
         * receive if it is less than transfer size and transfer size if
         * it is more. Enable the interrupts.
         */
        if (id->recv_count > CDNS_I2C_TRANSFER_SIZE)
                cdns_i2c_writereg(CDNS_I2C_TRANSFER_SIZE,
                                  CDNS_I2C_XFER_SIZE_OFFSET);
        else
                cdns_i2c_writereg(id->recv_count, CDNS_I2C_XFER_SIZE_OFFSET);
        /* Clear the bus hold flag if bytes to receive is less than FIFO size */
        if (!id->bus_hold_flag &&
                ((id->p_msg->flags & I2C_M_RECV_LEN) != I2C_M_RECV_LEN) &&
                (id->recv_count <= CDNS_I2C_FIFO_DEPTH))
                        cdns_i2c_clear_bus_hold(id);
        /* Set the slave address in address register - triggers operation */
        cdns_i2c_writereg(id->p_msg->addr & CDNS_I2C_ADDR_MASK,
                                                CDNS_I2C_ADDR_OFFSET);
        cdns_i2c_writereg(CDNS_I2C_ENABLED_INTR_MASK, CDNS_I2C_IER_OFFSET);
}

/**
 * cdns_i2c_msend - Prepare and start a master send operation
 * @id:         pointer to the i2c device
 */
static void cdns_i2c_msend(struct cdns_i2c *id)
{
        unsigned int avail_bytes;
        unsigned int bytes_to_send;
        unsigned int ctrl_reg;
        unsigned int isr_status;

        id->p_recv_buf = NULL;
        id->p_send_buf = id->p_msg->buf;
        id->send_count = id->p_msg->len;

        /* Set the controller in Master transmit mode and clear the FIFO. */
        ctrl_reg = cdns_i2c_readreg(CDNS_I2C_CR_OFFSET);
        ctrl_reg &= ~CDNS_I2C_CR_RW;
        ctrl_reg |= CDNS_I2C_CR_CLR_FIFO;

        /*
         * Check for the message size against FIFO depth and set the
         * 'hold bus' bit if it is greater than FIFO depth.
         */
        if (id->send_count > CDNS_I2C_FIFO_DEPTH)
                ctrl_reg |= CDNS_I2C_CR_HOLD;
        cdns_i2c_writereg(ctrl_reg, CDNS_I2C_CR_OFFSET);

        /* Clear the interrupts in interrupt status register. */
        isr_status = cdns_i2c_readreg(CDNS_I2C_ISR_OFFSET);
        cdns_i2c_writereg(isr_status, CDNS_I2C_ISR_OFFSET);

        /*
         * Calculate the space available in FIFO. Check the message length
         * against the space available, and fill the FIFO accordingly.
         * Enable the interrupts.
         */
        avail_bytes = CDNS_I2C_FIFO_DEPTH -
                                cdns_i2c_readreg(CDNS_I2C_XFER_SIZE_OFFSET);

        if (id->send_count > avail_bytes)
                bytes_to_send = avail_bytes;
        else
                bytes_to_send = id->send_count;

        while (bytes_to_send--) {
                cdns_i2c_writereg((*(id->p_send_buf)++), CDNS_I2C_DATA_OFFSET);
                id->send_count--;
        }

        /*
         * Clear the bus hold flag if there is no more data
         * and if it is the last message.
         */
        if (!id->bus_hold_flag && !id->send_count)
                cdns_i2c_clear_bus_hold(id);
        /* Set the slave address in address register - triggers operation. */
        cdns_i2c_writereg(id->p_msg->addr & CDNS_I2C_ADDR_MASK,
                                                CDNS_I2C_ADDR_OFFSET);

        cdns_i2c_writereg(CDNS_I2C_ENABLED_INTR_MASK, CDNS_I2C_IER_OFFSET);
}

/**
 * cdns_i2c_master_reset - Reset the interface
 * @adap:       pointer to the i2c adapter driver instance
 *
 * This function cleanup the fifos, clear the hold bit and status
 * and disable the interrupts.
 */
static void cdns_i2c_master_reset(struct i2c_adapter *adap)
{
        struct cdns_i2c *id = adap->algo_data;
        u32 regval;

        /* Disable the interrupts */
        cdns_i2c_writereg(CDNS_I2C_IXR_ALL_INTR_MASK, CDNS_I2C_IDR_OFFSET);
        /* Clear the hold bit and fifos */
        regval = cdns_i2c_readreg(CDNS_I2C_CR_OFFSET);
        regval &= ~CDNS_I2C_CR_HOLD;
        regval |= CDNS_I2C_CR_CLR_FIFO;
        cdns_i2c_writereg(regval, CDNS_I2C_CR_OFFSET);
        /* Update the transfercount register to zero */
        cdns_i2c_writereg(0, CDNS_I2C_XFER_SIZE_OFFSET);
        /* Clear the interupt status register */
        regval = cdns_i2c_readreg(CDNS_I2C_ISR_OFFSET);
        cdns_i2c_writereg(regval, CDNS_I2C_ISR_OFFSET);
        /* Clear the status register */
        regval = cdns_i2c_readreg(CDNS_I2C_SR_OFFSET);
        cdns_i2c_writereg(regval, CDNS_I2C_SR_OFFSET);
}

static int cdns_i2c_process_msg(struct cdns_i2c *id, struct i2c_msg *msg,
                struct i2c_adapter *adap)
{
        int ret;
        u32 reg;

        id->p_msg = msg;
        id->err_status = 0;
        reinit_completion(&id->xfer_done);

        /* Check for the TEN Bit mode on each msg */
        reg = cdns_i2c_readreg(CDNS_I2C_CR_OFFSET);
        if (msg->flags & I2C_M_TEN) {
                if (reg & CDNS_I2C_CR_NEA)
                        cdns_i2c_writereg(reg & ~CDNS_I2C_CR_NEA,
                                        CDNS_I2C_CR_OFFSET);
        } else {
                if (!(reg & CDNS_I2C_CR_NEA))
                        cdns_i2c_writereg(reg | CDNS_I2C_CR_NEA,
                                        CDNS_I2C_CR_OFFSET);
        }

        /* Check for the R/W flag on each msg */
        if (msg->flags & I2C_M_RD)
                cdns_i2c_mrecv(id);
        else
                cdns_i2c_msend(id);

        /* Wait for the signal of completion */
        ret = wait_for_completion_timeout(&id->xfer_done, adap->timeout);
        if (!ret) {
                cdns_i2c_master_reset(adap);
                dev_err(id->adap.dev.parent,
                                "timeout waiting on completion\n");
                return -ETIMEDOUT;
        }

        cdns_i2c_writereg(CDNS_I2C_IXR_ALL_INTR_MASK,
                          CDNS_I2C_IDR_OFFSET);

        /* If it is bus arbitration error, try again */
        if (id->err_status & CDNS_I2C_IXR_ARB_LOST)
                return -EAGAIN;

        return 0;
}

/**
 * cdns_i2c_master_xfer - The main i2c transfer function
 * @adap:       pointer to the i2c adapter driver instance
 * @msgs:       pointer to the i2c message structure
 * @num:        the number of messages to transfer
 *
 * Initiates the send/recv activity based on the transfer message received.
 *
 * Return: number of msgs processed on success, negative error otherwise
 */
static int cdns_i2c_master_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs,
                                int num)
{
        int ret, count;
        u32 reg;
        struct cdns_i2c *id = adap->algo_data;

        /* Check if the bus is free */
        if (cdns_i2c_readreg(CDNS_I2C_SR_OFFSET) & CDNS_I2C_SR_BA)
                return -EAGAIN;

        /*
         * Set the flag to one when multiple messages are to be
         * processed with a repeated start.
         */
        if (num > 1) {
                id->bus_hold_flag = 1;
                reg = cdns_i2c_readreg(CDNS_I2C_CR_OFFSET);
                reg |= CDNS_I2C_CR_HOLD;
                cdns_i2c_writereg(reg, CDNS_I2C_CR_OFFSET);
        } else {
                id->bus_hold_flag = 0;
        }

        /* Process the msg one by one */
        for (count = 0; count < num; count++, msgs++) {
                if (count == (num - 1))
                        id->bus_hold_flag = 0;

                ret = cdns_i2c_process_msg(id, msgs, adap);
                if (ret)
                        return ret;

                /* Report the other error interrupts to application */
                if (id->err_status) {
                        cdns_i2c_master_reset(adap);

                        if (id->err_status & CDNS_I2C_IXR_NACK)
                                return -ENXIO;

                        return -EIO;
                }
        }

        return num;
}

/**
 * cdns_i2c_func - Returns the supported features of the I2C driver
 * @adap:       pointer to the i2c adapter structure
 *
 * Return: 32 bit value, each bit corresponding to a feature
 */
static u32 cdns_i2c_func(struct i2c_adapter *adap)
{
        return I2C_FUNC_I2C | I2C_FUNC_10BIT_ADDR |
                (I2C_FUNC_SMBUS_EMUL & ~I2C_FUNC_SMBUS_QUICK) |
                I2C_FUNC_SMBUS_BLOCK_DATA;
}

static const struct i2c_algorithm cdns_i2c_algo = {
        .master_xfer    = cdns_i2c_master_xfer,
        .functionality  = cdns_i2c_func,
};

/**
 * cdns_i2c_calc_divs - Calculate clock dividers
 * @f:          I2C clock frequency
 * @input_clk:  Input clock frequency
 * @a:          First divider (return value)
 * @b:          Second divider (return value)
 *
 * f is used as input and output variable. As input it is used as target I2C
 * frequency. On function exit f holds the actually resulting I2C frequency.
 *
 * Return: 0 on success, negative errno otherwise.
 */
static int cdns_i2c_calc_divs(unsigned long *f, unsigned long input_clk,
                unsigned int *a, unsigned int *b)
{
        unsigned long fscl = *f, best_fscl = *f, actual_fscl, temp;
        unsigned int div_a, div_b, calc_div_a = 0, calc_div_b = 0;
        unsigned int last_error, current_error;

        /* calculate (divisor_a+1) x (divisor_b+1) */
        temp = input_clk / (22 * fscl);

        /*
         * If the calculated value is negative or 0, the fscl input is out of
         * range. Return error.
         */
        if (!temp || (temp > (CDNS_I2C_DIVA_MAX * CDNS_I2C_DIVB_MAX)))
                return -EINVAL;

        last_error = -1;
        for (div_a = 0; div_a < CDNS_I2C_DIVA_MAX; div_a++) {
                div_b = DIV_ROUND_UP(input_clk, 22 * fscl * (div_a + 1));

                if ((div_b < 1) || (div_b > CDNS_I2C_DIVB_MAX))
                        continue;
                div_b--;

                actual_fscl = input_clk / (22 * (div_a + 1) * (div_b + 1));

                if (actual_fscl > fscl)
                        continue;

                current_error = ((actual_fscl > fscl) ? (actual_fscl - fscl) :
                                                        (fscl - actual_fscl));

                if (last_error > current_error) {
                        calc_div_a = div_a;
                        calc_div_b = div_b;
                        best_fscl = actual_fscl;
                        last_error = current_error;
                }
        }

        *a = calc_div_a;
        *b = calc_div_b;
        *f = best_fscl;

        return 0;
}

/**
 * cdns_i2c_setclk - This function sets the serial clock rate for the I2C device
 * @clk_in:     I2C clock input frequency in Hz
 * @id:         Pointer to the I2C device structure
 *
 * The device must be idle rather than busy transferring data before setting
 * these device options.
 * The data rate is set by values in the control register.
 * The formula for determining the correct register values is
 *      Fscl = Fpclk/(22 x (divisor_a+1) x (divisor_b+1))
 * See the hardware data sheet for a full explanation of setting the serial
 * clock rate. The clock can not be faster than the input clock divide by 22.
 * The two most common clock rates are 100KHz and 400KHz.
 *
 * Return: 0 on success, negative error otherwise
 */
static int cdns_i2c_setclk(unsigned long clk_in, struct cdns_i2c *id)
{
        unsigned int div_a, div_b;
        unsigned int ctrl_reg;
        int ret = 0;
        unsigned long fscl = id->i2c_clk;

        ret = cdns_i2c_calc_divs(&fscl, clk_in, &div_a, &div_b);
        if (ret)
                return ret;

        ctrl_reg = cdns_i2c_readreg(CDNS_I2C_CR_OFFSET);
        ctrl_reg &= ~(CDNS_I2C_CR_DIVA_MASK | CDNS_I2C_CR_DIVB_MASK);
        ctrl_reg |= ((div_a << CDNS_I2C_CR_DIVA_SHIFT) |
                        (div_b << CDNS_I2C_CR_DIVB_SHIFT));
        cdns_i2c_writereg(ctrl_reg, CDNS_I2C_CR_OFFSET);

        return 0;
}

/**
 * cdns_i2c_clk_notifier_cb - Clock rate change callback
 * @nb:         Pointer to notifier block
 * @event:      Notification reason
 * @data:       Pointer to notification data object
 *
 * This function is called when the cdns_i2c input clock frequency changes.
 * 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.
 *
 * 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 cdns_i2c_clk_notifier_cb(struct notifier_block *nb, unsigned long
                event, void *data)
{
        struct clk_notifier_data *ndata = data;
        struct cdns_i2c *id = to_cdns_i2c(nb);

        if (id->suspended)
                return NOTIFY_OK;

        switch (event) {
        case PRE_RATE_CHANGE:
        {
                unsigned long input_clk = ndata->new_rate;
                unsigned long fscl = id->i2c_clk;
                unsigned int div_a, div_b;
                int ret;

                ret = cdns_i2c_calc_divs(&fscl, input_clk, &div_a, &div_b);
                if (ret) {
                        dev_warn(id->adap.dev.parent,
                                        "clock rate change rejected\n");
                        return NOTIFY_STOP;
                }

                /* scale up */
                if (ndata->new_rate > ndata->old_rate)
                        cdns_i2c_setclk(ndata->new_rate, id);

                return NOTIFY_OK;
        }
        case POST_RATE_CHANGE:
                id->input_clk = ndata->new_rate;
                /* scale down */
                if (ndata->new_rate < ndata->old_rate)
                        cdns_i2c_setclk(ndata->new_rate, id);
                return NOTIFY_OK;
        case ABORT_RATE_CHANGE:
                /* scale up */
                if (ndata->new_rate > ndata->old_rate)
                        cdns_i2c_setclk(ndata->old_rate, id);
                return NOTIFY_OK;
        default:
                return NOTIFY_DONE;
        }
}

/**
 * cdns_i2c_suspend - Suspend method for the driver
 * @_dev:       Address of the platform_device structure
 *
 * Put the driver into low power mode.
 *
 * Return: 0 always
 */
static int __maybe_unused cdns_i2c_suspend(struct device *_dev)
{
        struct platform_device *pdev = container_of(_dev,
                        struct platform_device, dev);
        struct cdns_i2c *xi2c = platform_get_drvdata(pdev);

        clk_disable(xi2c->clk);
        xi2c->suspended = 1;

        return 0;
}

/**
 * cdns_i2c_resume - Resume from suspend
 * @_dev:       Address of the platform_device structure
 *
 * Resume operation after suspend.
 *
 * Return: 0 on success and error value on error
 */
static int __maybe_unused cdns_i2c_resume(struct device *_dev)
{
        struct platform_device *pdev = container_of(_dev,
                        struct platform_device, dev);
        struct cdns_i2c *xi2c = platform_get_drvdata(pdev);
        int ret;

        ret = clk_enable(xi2c->clk);
        if (ret) {
                dev_err(_dev, "Cannot enable clock.\n");
                return ret;
        }

        xi2c->suspended = 0;

        return 0;
}

static SIMPLE_DEV_PM_OPS(cdns_i2c_dev_pm_ops, cdns_i2c_suspend,
                         cdns_i2c_resume);

/**
 * cdns_i2c_probe - Platform registration call
 * @pdev:       Handle to the platform device structure
 *
 * This function does all the memory allocation and registration for the i2c
 * device. User can modify the address mode to 10 bit address mode using the
 * ioctl call with option I2C_TENBIT.
 *
 * Return: 0 on success, negative error otherwise
 */
static int cdns_i2c_probe(struct platform_device *pdev)
{
        struct resource *r_mem;
        struct cdns_i2c *id;
        int ret;

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

        platform_set_drvdata(pdev, id);

        r_mem = platform_get_resource(pdev, IORESOURCE_MEM, 0);
        id->membase = devm_ioremap_resource(&pdev->dev, r_mem);
        if (IS_ERR(id->membase))
                return PTR_ERR(id->membase);

        id->irq = platform_get_irq(pdev, 0);

        id->adap.dev.of_node = pdev->dev.of_node;
        id->adap.algo = &cdns_i2c_algo;
        id->adap.timeout = CDNS_I2C_TIMEOUT;
        id->adap.retries = 3;           /* Default retry value. */
        id->adap.algo_data = id;
        id->adap.dev.parent = &pdev->dev;
        init_completion(&id->xfer_done);
        snprintf(id->adap.name, sizeof(id->adap.name),
                 "Cadence I2C at %08lx", (unsigned long)r_mem->start);

        id->clk = devm_clk_get(&pdev->dev, NULL);
        if (IS_ERR(id->clk)) {
                dev_err(&pdev->dev, "input clock not found.\n");
                return PTR_ERR(id->clk);
        }
        ret = clk_prepare_enable(id->clk);
        if (ret) {
                dev_err(&pdev->dev, "Unable to enable clock.\n");
                return ret;
        }
        id->clk_rate_change_nb.notifier_call = cdns_i2c_clk_notifier_cb;
        if (clk_notifier_register(id->clk, &id->clk_rate_change_nb))
                dev_warn(&pdev->dev, "Unable to register clock notifier.\n");
        id->input_clk = clk_get_rate(id->clk);

        ret = of_property_read_u32(pdev->dev.of_node, "clock-frequency",
                        &id->i2c_clk);
        if (ret || (id->i2c_clk > CDNS_I2C_SPEED_MAX))
                id->i2c_clk = CDNS_I2C_SPEED_DEFAULT;

        cdns_i2c_writereg(CDNS_I2C_CR_ACK_EN | CDNS_I2C_CR_NEA | CDNS_I2C_CR_MS,
                          CDNS_I2C_CR_OFFSET);

        ret = cdns_i2c_setclk(id->input_clk, id);
        if (ret) {
                dev_err(&pdev->dev, "invalid SCL clock: %u Hz\n", id->i2c_clk);
                ret = -EINVAL;
                goto err_clk_dis;
        }

        ret = devm_request_irq(&pdev->dev, id->irq, cdns_i2c_isr, 0,
                                 DRIVER_NAME, id);
        if (ret) {
                dev_err(&pdev->dev, "cannot get irq %d\n", id->irq);
                goto err_clk_dis;
        }

        ret = i2c_add_adapter(&id->adap);
        if (ret < 0) {
                dev_err(&pdev->dev, "reg adap failed: %d\n", ret);
                goto err_clk_dis;
        }

        dev_info(&pdev->dev, "%u kHz mmio %08lx irq %d\n",
                 id->i2c_clk / 1000, (unsigned long)r_mem->start, id->irq);

        return 0;

err_clk_dis:
        clk_disable_unprepare(id->clk);
        return ret;
}

/**
 * cdns_i2c_remove - Unregister the device after releasing the resources
 * @pdev:       Handle to the platform device structure
 *
 * This function frees all the resources allocated to the device.
 *
 * Return: 0 always
 */
static int cdns_i2c_remove(struct platform_device *pdev)
{
        struct cdns_i2c *id = platform_get_drvdata(pdev);

        i2c_del_adapter(&id->adap);
        clk_notifier_unregister(id->clk, &id->clk_rate_change_nb);
        clk_disable_unprepare(id->clk);

        return 0;
}

static const struct of_device_id cdns_i2c_of_match[] = {
        { .compatible = "cdns,i2c-r1p10", },
        { /* end of table */ }
};
MODULE_DEVICE_TABLE(of, cdns_i2c_of_match);

static struct platform_driver cdns_i2c_drv = {
        .driver = {
                .name  = DRIVER_NAME,
                .owner = THIS_MODULE,
                .of_match_table = cdns_i2c_of_match,
                .pm = &cdns_i2c_dev_pm_ops,
        },
        .probe  = cdns_i2c_probe,
        .remove = cdns_i2c_remove,
};

module_platform_driver(cdns_i2c_drv);

MODULE_AUTHOR("Xilinx Inc.");
MODULE_DESCRIPTION("Cadence I2C bus driver");
MODULE_LICENSE("GPL");