// SPDX-License-Identifier: GPL-2.0-only
/*
 *  Copyright Intel Corporation (C) 2017.
 *
 * Based on the i2c-axxia.c driver.
 */
#include <linux/clk.h>
#include <linux/clkdev.h>
#include <linux/err.h>
#include <linux/i2c.h>
#include <linux/iopoll.h>
#include <linux/interrupt.h>
#include <linux/module.h>
#include <linux/io.h>
#include <linux/kernel.h>
#include <linux/platform_device.h>

#define ALTR_I2C_TFR_CMD        0x00    /* Transfer Command register */
#define     ALTR_I2C_TFR_CMD_STA        BIT(9)  /* send START before byte */
#define     ALTR_I2C_TFR_CMD_STO        BIT(8)  /* send STOP after byte */
#define     ALTR_I2C_TFR_CMD_RW_D       BIT(0)  /* Direction of transfer */
#define ALTR_I2C_RX_DATA        0x04    /* RX data FIFO register */
#define ALTR_I2C_CTRL           0x08    /* Control register */
#define     ALTR_I2C_CTRL_RXT_SHFT      4       /* RX FIFO Threshold */
#define     ALTR_I2C_CTRL_TCT_SHFT      2       /* TFER CMD FIFO Threshold */
#define     ALTR_I2C_CTRL_BSPEED        BIT(1)  /* Bus Speed (1=Fast) */
#define     ALTR_I2C_CTRL_EN    BIT(0)  /* Enable Core (1=Enable) */
#define ALTR_I2C_ISER           0x0C    /* Interrupt Status Enable register */
#define     ALTR_I2C_ISER_RXOF_EN       BIT(4)  /* Enable RX OVERFLOW IRQ */
#define     ALTR_I2C_ISER_ARB_EN        BIT(3)  /* Enable ARB LOST IRQ */
#define     ALTR_I2C_ISER_NACK_EN       BIT(2)  /* Enable NACK DET IRQ */
#define     ALTR_I2C_ISER_RXRDY_EN      BIT(1)  /* Enable RX Ready IRQ */
#define     ALTR_I2C_ISER_TXRDY_EN      BIT(0)  /* Enable TX Ready IRQ */
#define ALTR_I2C_ISR            0x10    /* Interrupt Status register */
#define     ALTR_I2C_ISR_RXOF           BIT(4)  /* RX OVERFLOW IRQ */
#define     ALTR_I2C_ISR_ARB            BIT(3)  /* ARB LOST IRQ */
#define     ALTR_I2C_ISR_NACK           BIT(2)  /* NACK DET IRQ */
#define     ALTR_I2C_ISR_RXRDY          BIT(1)  /* RX Ready IRQ */
#define     ALTR_I2C_ISR_TXRDY          BIT(0)  /* TX Ready IRQ */
#define ALTR_I2C_STATUS         0x14    /* Status register */
#define     ALTR_I2C_STAT_CORE          BIT(0)  /* Core Status (0=idle) */
#define ALTR_I2C_TC_FIFO_LVL    0x18    /* Transfer FIFO LVL register */
#define ALTR_I2C_RX_FIFO_LVL    0x1C    /* Receive FIFO LVL register */
#define ALTR_I2C_SCL_LOW        0x20    /* SCL low count register */
#define ALTR_I2C_SCL_HIGH       0x24    /* SCL high count register */
#define ALTR_I2C_SDA_HOLD       0x28    /* SDA hold count register */

#define ALTR_I2C_ALL_IRQ        (ALTR_I2C_ISR_RXOF | ALTR_I2C_ISR_ARB | \
                                 ALTR_I2C_ISR_NACK | ALTR_I2C_ISR_RXRDY | \
                                 ALTR_I2C_ISR_TXRDY)

#define ALTR_I2C_THRESHOLD      0       /* IRQ Threshold at 1 element */
#define ALTR_I2C_DFLT_FIFO_SZ   4
#define ALTR_I2C_TIMEOUT        100000  /* 100ms */
#define ALTR_I2C_XFER_TIMEOUT   (msecs_to_jiffies(250))

/**
 * struct altr_i2c_dev - I2C device context
 * @base: pointer to register struct
 * @msg: pointer to current message
 * @msg_len: number of bytes transferred in msg
 * @msg_err: error code for completed message
 * @msg_complete: xfer completion object
 * @dev: device reference
 * @adapter: core i2c abstraction
 * @i2c_clk: clock reference for i2c input clock
 * @bus_clk_rate: current i2c bus clock rate
 * @buf: ptr to msg buffer for easier use.
 * @fifo_size: size of the FIFO passed in.
 * @isr_mask: cached copy of local ISR enables.
 * @isr_status: cached copy of local ISR status.
 * @isr_mutex: mutex for IRQ thread.
 */
struct altr_i2c_dev {
        void __iomem *base;
        struct i2c_msg *msg;
        size_t msg_len;
        int msg_err;
        struct completion msg_complete;
        struct device *dev;
        struct i2c_adapter adapter;
        struct clk *i2c_clk;
        u32 bus_clk_rate;
        u8 *buf;
        u32 fifo_size;
        u32 isr_mask;
        u32 isr_status;
        struct mutex isr_mutex;
};

static void
altr_i2c_int_enable(struct altr_i2c_dev *idev, u32 mask, bool enable)
{
        u32 int_en;

        int_en = readl(idev->base + ALTR_I2C_ISER);
        if (enable)
                idev->isr_mask = int_en | mask;
        else
                idev->isr_mask = int_en & ~mask;

        writel(idev->isr_mask, idev->base + ALTR_I2C_ISER);
}

static void altr_i2c_int_clear(struct altr_i2c_dev *idev, u32 mask)
{
        u32 int_en = readl(idev->base + ALTR_I2C_ISR);

        writel(int_en | mask, idev->base + ALTR_I2C_ISR);
}

static void altr_i2c_core_disable(struct altr_i2c_dev *idev)
{
        u32 tmp = readl(idev->base + ALTR_I2C_CTRL);

        writel(tmp & ~ALTR_I2C_CTRL_EN, idev->base + ALTR_I2C_CTRL);
}

static void altr_i2c_core_enable(struct altr_i2c_dev *idev)
{
        u32 tmp = readl(idev->base + ALTR_I2C_CTRL);

        writel(tmp | ALTR_I2C_CTRL_EN, idev->base + ALTR_I2C_CTRL);
}

static void altr_i2c_reset(struct altr_i2c_dev *idev)
{
        altr_i2c_core_disable(idev);
        altr_i2c_core_enable(idev);
}

static inline void altr_i2c_stop(struct altr_i2c_dev *idev)
{
        writel(ALTR_I2C_TFR_CMD_STO, idev->base + ALTR_I2C_TFR_CMD);
}

static void altr_i2c_init(struct altr_i2c_dev *idev)
{
        u32 divisor = clk_get_rate(idev->i2c_clk) / idev->bus_clk_rate;
        u32 clk_mhz = clk_get_rate(idev->i2c_clk) / 1000000;
        u32 tmp = (ALTR_I2C_THRESHOLD << ALTR_I2C_CTRL_RXT_SHFT) |
                  (ALTR_I2C_THRESHOLD << ALTR_I2C_CTRL_TCT_SHFT);
        u32 t_high, t_low;

        if (idev->bus_clk_rate <= I2C_MAX_STANDARD_MODE_FREQ) {
                tmp &= ~ALTR_I2C_CTRL_BSPEED;
                /* Standard mode SCL 50/50 */
                t_high = divisor * 1 / 2;
                t_low = divisor * 1 / 2;
        } else {
                tmp |= ALTR_I2C_CTRL_BSPEED;
                /* Fast mode SCL 33/66 */
                t_high = divisor * 1 / 3;
                t_low = divisor * 2 / 3;
        }
        writel(tmp, idev->base + ALTR_I2C_CTRL);

        dev_dbg(idev->dev, "rate=%uHz per_clk=%uMHz -> ratio=1:%u\n",
                idev->bus_clk_rate, clk_mhz, divisor);

        /* Reset controller */
        altr_i2c_reset(idev);

        /* SCL High Time */
        writel(t_high, idev->base + ALTR_I2C_SCL_HIGH);
        /* SCL Low Time */
        writel(t_low, idev->base + ALTR_I2C_SCL_LOW);
        /* SDA Hold Time, 300ns */
        writel(3 * clk_mhz / 10, idev->base + ALTR_I2C_SDA_HOLD);

        /* Mask all interrupt bits */
        altr_i2c_int_enable(idev, ALTR_I2C_ALL_IRQ, false);
}

/*
 * altr_i2c_transfer - On the last byte to be transmitted, send
 * a Stop bit on the last byte.
 */
static void altr_i2c_transfer(struct altr_i2c_dev *idev, u32 data)
{
        /* On the last byte to be transmitted, send STOP */
        if (idev->msg_len == 1)
                data |= ALTR_I2C_TFR_CMD_STO;
        if (idev->msg_len > 0)
                writel(data, idev->base + ALTR_I2C_TFR_CMD);
}

/*
 * altr_i2c_empty_rx_fifo - Fetch data from RX FIFO until end of
 * transfer. Send a Stop bit on the last byte.
 */
static void altr_i2c_empty_rx_fifo(struct altr_i2c_dev *idev)
{
        size_t rx_fifo_avail = readl(idev->base + ALTR_I2C_RX_FIFO_LVL);
        int bytes_to_transfer = min(rx_fifo_avail, idev->msg_len);

        while (bytes_to_transfer-- > 0) {
                *idev->buf++ = readl(idev->base + ALTR_I2C_RX_DATA);
                idev->msg_len--;
                altr_i2c_transfer(idev, 0);
        }
}

/*
 * altr_i2c_fill_tx_fifo - Fill TX FIFO from current message buffer.
 */
static int altr_i2c_fill_tx_fifo(struct altr_i2c_dev *idev)
{
        size_t tx_fifo_avail = idev->fifo_size - readl(idev->base +
                                                       ALTR_I2C_TC_FIFO_LVL);
        int bytes_to_transfer = min(tx_fifo_avail, idev->msg_len);
        int ret = idev->msg_len - bytes_to_transfer;

        while (bytes_to_transfer-- > 0) {
                altr_i2c_transfer(idev, *idev->buf++);
                idev->msg_len--;
        }

        return ret;
}

static irqreturn_t altr_i2c_isr_quick(int irq, void *_dev)
{
        struct altr_i2c_dev *idev = _dev;
        irqreturn_t ret = IRQ_HANDLED;

        /* Read IRQ status but only interested in Enabled IRQs. */
        idev->isr_status = readl(idev->base + ALTR_I2C_ISR) & idev->isr_mask;
        if (idev->isr_status)
                ret = IRQ_WAKE_THREAD;

        return ret;
}

static irqreturn_t altr_i2c_isr(int irq, void *_dev)
{
        int ret;
        bool read, finish = false;
        struct altr_i2c_dev *idev = _dev;
        u32 status = idev->isr_status;

        mutex_lock(&idev->isr_mutex);
        if (!idev->msg) {
                dev_warn(idev->dev, "unexpected interrupt\n");
                altr_i2c_int_clear(idev, ALTR_I2C_ALL_IRQ);
                goto out;
        }
        read = (idev->msg->flags & I2C_M_RD) != 0;

        /* handle Lost Arbitration */
        if (unlikely(status & ALTR_I2C_ISR_ARB)) {
                altr_i2c_int_clear(idev, ALTR_I2C_ISR_ARB);
                idev->msg_err = -EAGAIN;
                finish = true;
        } else if (unlikely(status & ALTR_I2C_ISR_NACK)) {
                dev_dbg(idev->dev, "Could not get ACK\n");
                idev->msg_err = -ENXIO;
                altr_i2c_int_clear(idev, ALTR_I2C_ISR_NACK);
                altr_i2c_stop(idev);
                finish = true;
        } else if (read && unlikely(status & ALTR_I2C_ISR_RXOF)) {
                /* handle RX FIFO Overflow */
                altr_i2c_empty_rx_fifo(idev);
                altr_i2c_int_clear(idev, ALTR_I2C_ISR_RXRDY);
                altr_i2c_stop(idev);
                dev_err(idev->dev, "RX FIFO Overflow\n");
                finish = true;
        } else if (read && (status & ALTR_I2C_ISR_RXRDY)) {
                /* RX FIFO needs service? */
                altr_i2c_empty_rx_fifo(idev);
                altr_i2c_int_clear(idev, ALTR_I2C_ISR_RXRDY);
                if (!idev->msg_len)
                        finish = true;
        } else if (!read && (status & ALTR_I2C_ISR_TXRDY)) {
                /* TX FIFO needs service? */
                altr_i2c_int_clear(idev, ALTR_I2C_ISR_TXRDY);
                if (idev->msg_len > 0)
                        altr_i2c_fill_tx_fifo(idev);
                else
                        finish = true;
        } else {
                dev_warn(idev->dev, "Unexpected interrupt: 0x%x\n", status);
                altr_i2c_int_clear(idev, ALTR_I2C_ALL_IRQ);
        }

        if (finish) {
                /* Wait for the Core to finish */
                ret = readl_poll_timeout_atomic(idev->base + ALTR_I2C_STATUS,
                                                status,
                                                !(status & ALTR_I2C_STAT_CORE),
                                                1, ALTR_I2C_TIMEOUT);
                if (ret)
                        dev_err(idev->dev, "message timeout\n");
                altr_i2c_int_enable(idev, ALTR_I2C_ALL_IRQ, false);
                altr_i2c_int_clear(idev, ALTR_I2C_ALL_IRQ);
                complete(&idev->msg_complete);
                dev_dbg(idev->dev, "Message Complete\n");
        }
out:
        mutex_unlock(&idev->isr_mutex);

        return IRQ_HANDLED;
}

static int altr_i2c_xfer_msg(struct altr_i2c_dev *idev, struct i2c_msg *msg)
{
        u32 imask = ALTR_I2C_ISR_RXOF | ALTR_I2C_ISR_ARB | ALTR_I2C_ISR_NACK;
        unsigned long time_left;
        u32 value;
        u8 addr = i2c_8bit_addr_from_msg(msg);

        mutex_lock(&idev->isr_mutex);
        idev->msg = msg;
        idev->msg_len = msg->len;
        idev->buf = msg->buf;
        idev->msg_err = 0;
        reinit_completion(&idev->msg_complete);
        altr_i2c_core_enable(idev);

        /* Make sure RX FIFO is empty */
        do {
                readl(idev->base + ALTR_I2C_RX_DATA);
        } while (readl(idev->base + ALTR_I2C_RX_FIFO_LVL));

        writel(ALTR_I2C_TFR_CMD_STA | addr, idev->base + ALTR_I2C_TFR_CMD);

        if ((msg->flags & I2C_M_RD) != 0) {
                imask |= ALTR_I2C_ISER_RXOF_EN | ALTR_I2C_ISER_RXRDY_EN;
                altr_i2c_int_enable(idev, imask, true);
                /* write the first byte to start the RX */
                altr_i2c_transfer(idev, 0);
        } else {
                imask |= ALTR_I2C_ISR_TXRDY;
                altr_i2c_int_enable(idev, imask, true);
                altr_i2c_fill_tx_fifo(idev);
        }
        mutex_unlock(&idev->isr_mutex);

        time_left = wait_for_completion_timeout(&idev->msg_complete,
                                                ALTR_I2C_XFER_TIMEOUT);
        mutex_lock(&idev->isr_mutex);
        altr_i2c_int_enable(idev, imask, false);

        value = readl(idev->base + ALTR_I2C_STATUS) & ALTR_I2C_STAT_CORE;
        if (value)
                dev_err(idev->dev, "Core Status not IDLE...\n");

        if (time_left == 0) {
                idev->msg_err = -ETIMEDOUT;
                dev_dbg(idev->dev, "Transaction timed out.\n");
        }

        altr_i2c_core_disable(idev);
        mutex_unlock(&idev->isr_mutex);

        return idev->msg_err;
}

static int
altr_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
{
        struct altr_i2c_dev *idev = i2c_get_adapdata(adap);
        int i, ret;

        for (i = 0; i < num; i++) {
                ret = altr_i2c_xfer_msg(idev, msgs++);
                if (ret)
                        return ret;
        }
        return num;
}

static u32 altr_i2c_func(struct i2c_adapter *adap)
{
        return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL;
}

static const struct i2c_algorithm altr_i2c_algo = {
        .xfer = altr_i2c_xfer,
        .functionality = altr_i2c_func,
};

static int altr_i2c_probe(struct platform_device *pdev)
{
        struct altr_i2c_dev *idev = NULL;
        int irq, ret;

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

        idev->base = devm_platform_ioremap_resource(pdev, 0);
        if (IS_ERR(idev->base))
                return PTR_ERR(idev->base);

        irq = platform_get_irq(pdev, 0);
        if (irq < 0)
                return irq;

        idev->i2c_clk = devm_clk_get(&pdev->dev, NULL);
        if (IS_ERR(idev->i2c_clk)) {
                dev_err(&pdev->dev, "missing clock\n");
                return PTR_ERR(idev->i2c_clk);
        }

        idev->dev = &pdev->dev;
        init_completion(&idev->msg_complete);
        mutex_init(&idev->isr_mutex);

        ret = device_property_read_u32(idev->dev, "fifo-size",
                                       &idev->fifo_size);
        if (ret) {
                dev_err(&pdev->dev, "FIFO size set to default of %d\n",
                        ALTR_I2C_DFLT_FIFO_SZ);
                idev->fifo_size = ALTR_I2C_DFLT_FIFO_SZ;
        }

        ret = device_property_read_u32(idev->dev, "clock-frequency",
                                       &idev->bus_clk_rate);
        if (ret) {
                dev_err(&pdev->dev, "Default to 100kHz\n");
                idev->bus_clk_rate = I2C_MAX_STANDARD_MODE_FREQ;        /* default clock rate */
        }

        if (idev->bus_clk_rate > I2C_MAX_FAST_MODE_FREQ) {
                dev_err(&pdev->dev, "invalid clock-frequency %d\n",
                        idev->bus_clk_rate);
                return -EINVAL;
        }

        ret = devm_request_threaded_irq(&pdev->dev, irq, altr_i2c_isr_quick,
                                        altr_i2c_isr, IRQF_ONESHOT,
                                        pdev->name, idev);
        if (ret) {
                dev_err(&pdev->dev, "failed to claim IRQ %d\n", irq);
                return ret;
        }

        ret = clk_prepare_enable(idev->i2c_clk);
        if (ret) {
                dev_err(&pdev->dev, "failed to enable clock\n");
                return ret;
        }

        mutex_lock(&idev->isr_mutex);
        altr_i2c_init(idev);
        mutex_unlock(&idev->isr_mutex);

        i2c_set_adapdata(&idev->adapter, idev);
        strscpy(idev->adapter.name, pdev->name, sizeof(idev->adapter.name));
        idev->adapter.owner = THIS_MODULE;
        idev->adapter.algo = &altr_i2c_algo;
        idev->adapter.dev.parent = &pdev->dev;
        idev->adapter.dev.of_node = pdev->dev.of_node;

        platform_set_drvdata(pdev, idev);

        ret = i2c_add_adapter(&idev->adapter);
        if (ret) {
                clk_disable_unprepare(idev->i2c_clk);
                return ret;
        }
        dev_info(&pdev->dev, "Altera SoftIP I2C Probe Complete\n");

        return 0;
}

static void altr_i2c_remove(struct platform_device *pdev)
{
        struct altr_i2c_dev *idev = platform_get_drvdata(pdev);

        clk_disable_unprepare(idev->i2c_clk);
        i2c_del_adapter(&idev->adapter);
}

/* Match table for of_platform binding */
static const struct of_device_id altr_i2c_of_match[] = {
        { .compatible = "altr,softip-i2c-v1.0" },
        {},
};
MODULE_DEVICE_TABLE(of, altr_i2c_of_match);

static struct platform_driver altr_i2c_driver = {
        .probe = altr_i2c_probe,
        .remove = altr_i2c_remove,
        .driver = {
                .name = "altera-i2c",
                .of_match_table = altr_i2c_of_match,
        },
};

module_platform_driver(altr_i2c_driver);

MODULE_DESCRIPTION("Altera Soft IP I2C bus driver");
MODULE_AUTHOR("Thor Thayer <thor.thayer@linux.intel.com>");
MODULE_LICENSE("GPL v2");